bluuebunny/crossref_metadata_2025_split huggingface dataset:
Amido‐thioether polymers containing pendant carboxylato groups: thermodynamics of protonation and copper(II) complex formation in dilute aqueous solution
Authors: Casolaro Mario , Ranucci Elisabetta , Bignotti Fabio , Ferruti Paolo 
Published: April 2003

AbstractCalorimetric data are reported for the enthalpy of protonation of pendant carboxylato groups in new polymers 1a–d containing amido and thioether moieties in their main chain. These data, together with potentiometric and viscometric data, afford a complete thermodynamic description of the protonation process of the new polyacids, which are water‐soluble in a narrow range of α (degree of protonation) values. Comparison with the non‐macromolecular model 2 revealed that the thermodynamic features are attributable to polyelectrolyte effects. In contrast with model 2, all polymers studied form stable hydroxocomplex species with copper(II) ion. The hypothesized [Cu(OH)2L2]2− (where L is the monomeric unit of the polymer) stoichiometry fits the potentiometric data well when processed with the ‘SUPERFIT’ program. The trend of the corresponding stability constant (log β) values is to decrease with increasing pH over a wide range.
The post‐irradiation oxidation of poly(propylene), 1. Radical decay and oxygen absorption
Authors: Geuskens Georges , Nedelkos Grigorios 
Published: April 2003

AbstractThe oxidation of poly(propylene) following gamma irradiation was studied by means of electron spin resonance spectroscopy, hydroperoxide analysis and oxygen absorption measurements. Most peroxy radicals trapped after irradiation are mobile and decay within a week as a consequence of a migration process involving oxygen absorption and production of hydroperoxides. During that initial stage, the rate of oxygen absorption decreases proportionally to the peroxy radical concentration. Afterwards, the concentration of peroxy radicals becomes practically stationary and the rates of oxygen absorption and of hydroperoxide production remain constant for more than a year. That second stage of post‐irradiation oxidation of poly(propylene) is initiated by the slow decomposition of clustered hydroperoxides that proceeds even in the dark at room temperature.
Kinetics of radical polymerization, 55. The polymerization of p‐methylstyrene in solution
Authors: Gyöngyhalmi I. , Nagy A. , Földes‐Bereznich T. , Tüdős F. 
Published: April 2003

AbstractRadical polymerization of p‐methylstyrene was studied in benzene solution at 50°C using AIBN as the initiator. The rate of inititation was determined at various dilutions; it shows a slight linear dependence on the composition of the polymerization mixture. The polymerization rate is directly proportional to the square root of initiator concentration; however, in contrast to the classical kinetic picture, it is not directly proportional to the monomer concentration. The experimentally measured solvent effect can be interpreted neither by the diffusion theory nor by the EDA theory, it is, however, quantitatively consistent with the theory of hot radicals. The so‐called absolute values of the rate constants of chain propagation (k̄2) and chain termination (k4) were determined by means of the rotating sector method. The value of k4 was found to be constant within the limits of experimental error, consequently the experimentally observed solvent effect is caused solely by the change in the chain propagation rate constant.
Melting behavior of hydrolyzable poly(oxyethylene)/poly(L‐lactide) copolymers
Authors: Liu Hsin‐Jiant , Hu David Shiaw‐Guang 
Published: April 2003

AbstractThe melting behavior of poly(oxyethylene) (PEG)/poly(L‐lactide) (PLLA) triblock copolymers with PEG contents ≦18,3 wt.‐% was studied by differential scanning calorimetry and polarizing optical microscopy. The influence of the PEG segment contents and the hydrolysis of the PEG/PLLA copolymers on the melting process was investigated. The melting temperatures of the PLLA homopolymers decrease with increasing hydrolysis time up to 600 h, and the degree of crystallinity increases from 46 to 56%. This causes the arrangement of the chains more ordered. Therefore, the entropies of fusion (ΔSm) of the PLLA homopolymers increase during the hydrolysis time up to 600 h. The melting temperatures of the PEG/PLLA copolymers decrease, while the recrystallization temperatures increase with increasing hydrolysis time up to 600 h. In addition, both the increases of PEG content and hydrolysis time of the PEG/PLLA copolymers cause a decrease of ΔSm. The PEG segments and the hydrolysis are responsible for the disordered arrangement of the chains.
Cationic polymerization of α‐pinene with aluminium‐based binary catalysts, 3. Effects of added base
Authors: Higashimura Toshinobu , Lu Jiang , Kamigaito Masami , Sawamoto Mitsuo , Deng Yun‐Xiang 
Published: April 2003

AbstractIn the presence of nucleophilic additives such as esters (ethyl benzoate, acetate, and chloroacetate), ethers (diethyl ether and 1,4‐dioxane), and ammonium salts (nBu4NCl), oligomers of α‐pinene with relatively high molecular weights (M̄n ≥ 1000) were obtained with the AlCl3/SbCl3 binary catalyst in toluene at 0°C ([AlCl3]0 = 42,5 mmol · L−1, Sb/Al = 0,50, [additive]0 = 10,6 mmol · L−1). The yield was 80–90 wt.‐%, and the dimer content was as low as 6 wt.‐%. Also in the polymerization at 25°C, the addition of ethyl benzoate increased the oligomer's average molecular weight (M̄n = 850) and decreased the dimer content (10 wt.‐%), in contrast to the low M̄n (350) and the high dimer content (40 wt.‐%) in the absence of the additive. The oligomers obtained in the presence of ethyl benzoate contained the repeating unit 1 which has an endo‐olefin group, at higher ratio than in the absence of the additive. Phenomenologically, the role of the additives is to retard the polymerization so as to proceed at a moderate rate even at high temperature above 0°C and thereby to suppress the dimer formation.
Molecular dynamics of new thermoplastic elastomers based on hydrogen bonding complexes: a deuteron nuclear magnetic resonance investigation
Authors: Dardin Alexander , Stadler Reimund , Boeffel Christine , Spiess Hans Wolfgang 
Published: April 2003

Abstract4‐(4‐Carboxyphenyl)‐3,5‐dioxo‐1,2,4‐triazolidin‐1‐yl moieties resulting from 4‐(3,5‐dioxo‐1,2,4‐triazolin‐4‐yl)benzoic acid (U4A) randomly attached to 1,4‐polybutadiene form supramolecular aggregates which act as effective junction zones in new thermoplastic elastomers. Deuteron nuclear magnetic resonance (2H NMR) spectroscopy was used to investigate the molecular dynamics of the polymer backbone and the junction zones in selectively labelled samples. The spectra show motional heterogeneity along the polymer chain as well as in the supramolecular domains. Polybutadiene segments which are adjacent to these polar clusters are restricted in their mobility, even at temperatures 100 K above the glass transition temperature Tg. The immobilized regions are estimated to involve about two monomeric units. The functional groups in the supramolecular structures are rigid or exhibit 180° ‐phenyl flips dependent on their location in the middle or in the edges, respectively. Polar units which are not enclosed in the clusters and dispersed in the polymer matrix undergo fast isotropic motions.
Activation of SiO2‐supported zirconocene catalysts by common trialkylaluminiums
Authors: Soga Kazuo , Shiono Takeshi , Kim Hyun Joon 
Published: April 2003

AbstractA modified SiO2 was prepared by reacting SiO2 with Cl2Si(CH3)2 in toluene, on which methylaluminoxane (MAO) was supported to obtain a catalyst precursor. The mixture of the precursor and Cp2ZrCl2 (Cp: cyclopentadienyl) gave polyethylene in a high yield even by using common trialkylaluminiums as cocatalyst. Surprisingly, the MAO‐free catalyst system composed of the modified SiO2 and Cp2ZrCl2 was also found to be activated by common trialkylaluminiums.
Coordinated pair chain folding model for solution‐grown polyethylene single crystal
Authors: Hu Andrew Teh , Chang Hwei‐Liang 
Published: April 2003

AbstractA new regular chain folding model, namely the “coordinated pair chain folding model” (CPCFM) is proposed to revive the consideration that a polymer chain should fold regularly rather than randomly in solution‐grown polyethylene single crystals.
Influence of aryl substituents on the thermal and solubility behavior of poly(p‐phenylene terephthalate) and poly(p‐phenylene terephthalamide)
Authors: Hatke Wilfried , Land Horst‐Tore , Schmidt Hans‐Werner , Heitz Walter 
Published: April 2003

AbstractThe substitution of poly(p‐phenylene terephthalate) and poly(p‐phenylene terephthalamide) with phenyl and biphenylyl substituents (4‐biphenylyl and 2‐biphenylyl) in the terephthalic acid unit lowers the melting temperatures and crystallization tendency and increases the solubility. The melting temperatures of the polyesters are in the range of 285–350°C. Melting of the polyamides occurs between 440–490°C. The polyamides begin to decompose in the same temperature range. In polyesters as well as in polyamides the 2‐biphenylyl substituent was found to be more effective in decreasing the crystallinity, lowering the melt transition temperatures and increasing the solubility.
Decreased viability of nitric oxide synthase double knockout mice
Authors: Tranguch Susanne , Huet‐Hudson Yvette 
Published: April 2003

AbstractNitric oxide acts as an important intracellular messenger in a variety of systems, including reproduction. Previous studies have shown the importance of nitric oxide in embryo development. NO is produced from l‐arginine by the enzyme, nitric oxide synthase (NOS), which has three isoforms: endothelial (NOS3), neural (NOS1), and inducible (NOS2). We hypothesize that, because of the importance of NOS in development, at least two NOS isoforms are required in order for normal embryo development to occur. Through the generation of NOS3/NOS2, NOS3/NOS1, and NOS2/NOS1 double knockout mice, we found that while litter size remains unchanged, the expected number of generated double knockout mice varies significantly from what would be predicted by Mendelian genetics. Estrous cycles were similar for both DKO and the wild‐type mice, and both groups were deemed fertile by their ability to mate with wild‐type (CD‐1) mice. Together, these results lead us to conclude that the lack of two NOS isoforms leads to a decreased viability in mice because of a developmental problem in the double knockout embryo. Mol. Reprod. Dev. 65: 175–179, 2003. © 2003 Wiley‐Liss, Inc.
Effects of cooling on meiotic spindle structure and chromosome alignment within in vitro matured porcine oocytes
Authors: Liu Rui‐Hua , Sun Qing‐Yuan , Li Yong‐Hai , Jiao Li‐Hong , Wang Wei‐Hua 
Published: April 2003

AbstractMeiotic spindle structure and chromosome alignment were examined after porcine oocytes were cooled at metaphase II (M II) stage. Cumulus–oocyte complexes (COCs) collected from medium size follicles were cultured in an oocyte maturation medium at 39°C, 5% CO2 in air for 44 hr. At the end of culture, oocytes were removed from cumulus cells and cooled to 24 or 4°C for 5, 30, or 120 min in a solution with or without 1.5 M dimethyl sulfoxide (DMSO). After being cooled, oocytes were either fixed immediately for examination of the meiotic spindle and chromosome alignment or returned to maturation medium at 39°C for 2 hr for examination of spindle recovery. Most oocytes (65–71%) cooled to 24°C showed partially depolymerized spindles but 81–92% of oocytes cooled at 4°C did not have a spindle after cooling for 120 min. Quicker disassembly of spindles in the oocytes was observed at 4°C than at 24°C. Cooling also induced chromosome abnormality, which was indicated by dispersed chromosomes in the cytoplasm. Limited spindle recovery was observed in the oocytes cooled to both 4 and 24°C regardless of cooling time. The effect of cooling on the spindle organization and chromosome alignment was not influenced by the presence of DMSO. These results indicate that the meiotic spindles in porcine M II oocytes are very sensitive to a drop in the temperature. Both spindle and chromosomes were damaged during cooling, and such damage was not reversible by incubating the oocytes after they had been cooled. Mol. Reprod. Dev. 65: 212–218, 2003. © 2003 Wiley‐Liss, Inc.
Effects of exogenous hexoses on bovine in vitro fertilized and cloned embryo development: Improved blastocyst formation after glucose replacement with fructose in a serum‐free culture medium
Authors: Kwun Jean , Chang Kyunghee , Lim Jeongmook , Lee Eunsong , Lee Byeongchun , Kang Sungkeun , Hwang Woosuk 
Published: April 2003

AbstractTo evaluate the embryotrophic role of three hexoses (glucose, fructose, and galactose), bovine embryos derived from somatic cell nuclear transfer (SCNT) or in vitro‐fertilization (IVF) were cultured in a modified synthetic oviductal fluid (mSOF), which contained either glucose (1.5 or 5.6 mM), fructose (1.5 or 5.6 mM), or galactose (1.5 or 5.6 mM). Compared to 1.5 mM glucose, use of 1.5 mM fructose significantly enhanced blastocyst formation in both SCNT (23 vs. 33%) and IVF embryos (26 vs. 34%), while 5.6 mM fructose did not improve blastocyst formation. Using 1.5 mM galactose did not improve blastocyst formation in SCNT embryos (22 vs. 23%), whereas it significantly inhibited blastocyst formation in IVF embryos (26 vs. 0%). In both SCNT and IVF embryos, 5.6 mM glucose or galactose significantly inhibited embryo development. In a second experiment, in glucose‐free mSOF, fructose at concentrations of 0.75, 1.5, 3.0, or 5.6 mM was able to support to morula (32–42 vs. 12%) and blastocyst formation (30–38 vs. 12%) compared to 0 mM fructose. In Experiment 3, addition of fructose (1.5, 3.0, or 5.6 mM) to mSOF containing 1.5 mM glucose did not further promote blastocyst formation in SCNT embryos compared with replacement with 1.5 mM fructose only. Replacement of glucose with 1.5 mM fructose significantly increased total blastomeres (143 vs. 123 cells) and trophectodermal (TE) cells (116 vs. 94 cells) and decreased inner cell mass (ICM) to TE cell ratio (0.24 vs. 0.31) in blastocysts, compared to 1.5 mM glucose. The combined addition of 1.5 mM fructose and glucose significantly increased ICM cell number (36.7 cells) and ICM/TE ratio (0.46). In conclusion, fructose might be a more efficient energy substrate than glucose for producing large number of transferable blastocysts derived from SCNT. Mol. Reprod. Dev. 65: 167–174, 2003. © 2003 Wiley‐Liss, Inc.
Functional perfusion imaging using continuous arterial spin labeling with separate labeling and imaging coils at 3 T
Authors: Mildner Toralf , Trampel Robert , Möller Harald E. , Schäfer Andreas , Wiggins Christopher J. , Norris David G. 
Published: April 2003

AbstractFunctional perfusion imaging with a separate labeling coil located above the common carotid artery was demonstrated in human volunteers at 3 T. A helmet resonator and a spin‐echo echo‐planar imaging (EPI) sequence were used for imaging, and a circular surface coil of 6 cm i.d. was employed for labeling. The subjects performed a finger‐tapping task. Signal differences between the condition of finger tapping and the resting state were between −0.5% and −1.1 % among the subjects. The imaging protocol included a long post‐label delay (PLD) to reduce transit time effects. Labeling was applied for all repetitions of the functional run to reduce the sampling interval. Magn Reson Med 49:791–795, 2003. © 2003 Wiley‐Liss, Inc.
Comparison of temporal filtering methods for dynamic contrast MRI myocardial perfusion studies
Authors: Di Bella E.V.R. , Wu Y.J. , Alexander A.L. , Parker D.L. , Green D. , McGann C.J. 
Published: April 2003

AbstractDynamic contrast myocardial perfusion studies may benefit from methods that speed up the acquisition. Unaliasing by Fourier encoding the overlaps using the temporal dimension (UNFOLD), and a similar linear interpolation method have been shown to be effective at reducing the number of phase encodes needed for cardiac wall motion studies by using interleaved sampling and temporal filtering. Here such methods are evaluated in cardiac dynamic contrast studies, with particular regard to the effects of the choice of filter and the interframe motion. Four different filters were evaluated using a motion‐free canine study. Full k‐space was acquired and then downsampled to allow for a measure of truth. The different filters gave nearly equivalent images and quantitative flow estimates compared to full k‐space. The effect of respiratory motion on these schemes was graphically depicted, and the performance of the four temporal filters was evaluated in seven human subjects with respiratory motion present. The four filters provided images of similar quality. However, none of the filters were effective at eliminating motion artifacts. Motion registration methods or motion‐free acquisitions may be necessary to make these reduced FOV approaches clinically useful. Magn Reson Med 49:895–902, 2003. © 2003 Wiley‐Liss, Inc.
Hemodynamic segmentation of MR brain perfusion images using independent component analysis, thresholding, and Bayesian estimation
Authors: Kao Yi‐Hsuan , Guo Wan‐Yuo , Wu Yu‐Te , Liu Kuo‐Ching , Chai Wen‐Yen , Lin Chiao‐Yuan , Hwang Yi‐Shuan , Jy‐Kang Liou Adrain , Wu Hsiu‐Mei , Cheng Hui‐Cheng , Yeh Tzu‐Chen , Hsieh Jen‐Chuen , Mu Huo Teng Michael 
Published: April 2003

AbstractDynamic‐susceptibility‐contrast MR perfusion imaging is a widely used imaging tool for in vivo study of cerebral blood perfusion. However, visualization of different hemodynamic compartments is less investigated. In this work, independent component analysis, thresholding, and Bayesian estimation were used to concurrently segment different tissues, i.e., artery, gray matter, white matter, vein and sinus, choroid plexus, and cerebral spinal fluid, with corresponding signal–time curves on perfusion images of five normal volunteers. Based on the spatiotemporal hemodynamics, sequential passages and microcirculation of contrast‐agent particles in these tissues were decomposed and analyzed. Late and multiphasic perfusion, indicating the presence of contrast agents, was observed in the choroid plexus and the cerebral spinal fluid. An arterial input function was modeled using the concentration–time curve of the arterial area on the same slice, rather than remote slices, for the deconvolution calculation of relative cerebral blood flow. Magn Reson Med 49:885–894, 2003. © 2003 Wiley‐Liss, Inc.
Artifact reduction in true‐FISP imaging of the coronary arteries by adjusting imaging frequency
Authors: Deshpande Vibhas S. , Shea Steven M. , Li Debiao 
Published: April 2003

AbstractThe presence of resonance frequency offsets often causes artifacts in images acquired with true fast imaging with steady‐state precession (true‐FISP). One source of resonance offsets is a suboptimal setting of the synthesizer frequency. The goal of this work was to demonstrate that shifting the synthesizer frequency could minimize the off‐resonance related image artifacts in true‐FISP. A simple scouting method was developed to estimate the optimal synthesizer frequency for the volume of interest (VOI). To improve fat suppression, a similar scouting method was also developed to determine the optimal frequency offset for the fat saturation pulse. Coronary artery imaging was performed in healthy subjects using a 3D true‐FISP sequence to validate the effectiveness of the frequency corrections. Substantial reduction in image artifacts and improvement in fat suppression were observed by using the water and fat frequencies estimated by the scouting scans. Frequency shifting is a useful and practical method for improving coronary artery imaging using true‐FISP. Magn Reson Med 49:803–809, 2003. © 2003 Wiley‐Liss, Inc.
Localized proton MRS of cerebral metabolite profiles in different mouse strains
Authors: Schwarcz Attila , Natt Oliver , Watanabe Takashi , Boretius Susann , Frahm Jens , Michaelis Thomas 
Published: April 2003

AbstractLocalized proton MR spectroscopy (MRS) was used to quantify cerebral metabolite concentrations in NMRI (n = 8), BALB/c (n = 7), and C57BL/6 (n = 8) mice in vivo and 1 hr after global irreversible ischemia (2.35 T, STEAM, TR/TE/TM = 6000/20/10 ms, 4 × 3 × 4 mm3 volume, corrections for cerebrospinal fluid). Anatomical MRI and proton MRS revealed significant differences of the C57BL/6 strain in comparison with both BALB/c and NMRI mice. While MRI volumetry yielded larger ventricular spaces of the C57BL/6 strain, proton MRS resulted in elevated concentrations of N‐acetylaspartate (tNAA), creatine and phosphocreatine (tCr), choline‐containing compounds (Cho), glucose (Glc), and lactate (Lac) relative to BALB/c mice and elevated Glc relative to NMRI mice. Apart from the expected decrease of Glc and increase of Lac 1 hr post mortem, C57BL/6 mice presented with significant reductions of tNAA, tCr, and Cho, whereas these metabolites remained unchanged in BALB/c and NMRI mice. The results support the hypothesis that the more pronounced vulnerability of C57BL/6 mice to brain ischemia is linked to strain‐dependent differences of the cerebral energy metabolism. Magn Reson Med 49:822–827, 2003. © 2003 Wiley‐Liss, Inc.
Dynamic, contrast‐enhanced perfusion MRI in mouse gliomas: Correlation with histopathology
Authors: Cha Soonmee , Johnson Glyn , Wadghiri Youssef Zaim , Jin Olivier , Babb Jim , Zagzag David , Turnbull Daniel H. 
Published: April 2003

AbstractThe aim of this study was to develop an MRI protocol to evaluate the growth and vascularity of implanted GL261 mouse gliomas on a 7T microimaging system. Both conventional T1‐ and T2‐weighted imaging and dynamic, contrast‐enhanced T2*‐weighted imaging were performed on 34 mice at different stages of tumor development. MRI measurements of relative cerebral blood volume (rCBV) were compared to histological assessments of microvascular density (MVD). Enhancement on postcontrast T1‐weighted images was compared to histological assessments of Evan's blue extravasation. Conventional T2‐weighted and postcontrast T1‐weighted images demonstrated tumor growth characteristics consistent with previous descriptions of GL261 glioma. Furthermore, measurements of rCBV from MRI data were in good agreement with histological measurements of MVD from the same tumors. Postcontrast enhancement on T1‐weighted images was observed at all stages of GL261 glioma progression, even before evidence of angiogenesis, indicating that the mechanism of conventional contrast enhancement in MRI does not require neovascularization. These results provide quantitative support for MRI approaches currently used to assess human brain tumors, and form the basis for future studies of angiogenesis in genetically engineered mouse brain tumor models. Magn Reson Med 49:848–855, 2003. © 2003 Wiley‐Liss, Inc.