bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Metallocene Structures on their Performance in Ethene Polymerisation
Authors: Piel Tanja , Saarinen Tapio , Löfgren Barbro , Kokko Esa , Maaranen Janne , Pitkänen Päivi 
Published: April 2007

AbstractSix (Cp)(4‐phenyl‐indenyl)MCl2 (A) and four (Cp)(1‐phenyl‐indenyl)MCl2 (C) (M = Zr/Hf) based complexes were tested in ethene homo‐ and copolymerisation under different conditions to explain how the differences in the complex structure affect the polymerisation process and the formed polymer. Polymerisation experiments reveal that hafnocene catalysts need a higher amount of MAO to reach the maximum activity than zirconocenes. Hafnocenes also incorporate better 1‐hexene. Catalysts with the Cp* or 1,2,4‐Me3Cp ligand show higher activity, and work well with [HNMe2Ph][B(C6F5)4]/TIBA as cocatalyst, but produce polymers with lower $\overline M _{\rm n} $ than the corresponding catalyst with a plain Cp ligand. The Cp* ligand seems to prevent 1‐hexene incorporation. A methyl group in the 2‐position of (Cp)(4‐PhInd)ZrCl2 decreases the activity and $\overline M _{\rm n} $ but favours 1‐hexene insertion. Polymerisation activity is higher with catalysts with a 1‐PhInd‐ligand than with a 4‐PhInd‐ligand.magnified image
Synthesis and Properties of Helical Polyacetylenes Carrying Cholesteryl Moieties
Authors: Qu Jinqing , Shiotsuki Masashi , Sanda Fumio , Masuda Toshio 
Published: April 2007

AbstractNovel acetylene monomers containing cholesteryl groups, N‐cholesteryloxycarbonyl‐2‐ethynylcarbazole (1) and cholesteryl N‐propargylcarbamate (2) were synthesized and polymerized with an Rh catalyst to give the corresponding polymers [poly(1) and poly(2)] with $\overline M _{\rm n} $ of 22 600 and 26 600 in 56% and 95% yields, respectively. CD spectroscopic studies revealed that poly(1) and poly(2) took predominantly one‐handed helical structure in CHCl3, THF, and toluene. The helical structure of poly(1) remarkably changed upon temperature, while that of poly(2) was stable against heating. The helix of poly(2) was relatively stable to the addition of MeOH, but largely affected by the composition of CHCl3 and toluene. Poly(1) exhibited no clear oxidation peak, but a clear reduction peak at 0.65 V in cyclic voltammetry. Poly(1) and poly(2) showed liquid crystalline properties.magnified image
Anionic Synthesis of Epoxy End‐Capped Polymers
Authors: Ji Haining , Farmer Brandon S. , Nonidez William K. , Advincula Rigoberto C. , Smith Grant D. , Kilbey S. Michael , Dadmun Mark D. , Mays Jimmy W. 
Published: April 2007

AbstractThe reaction of living anions of polystyrene (PS) or poly(methyl methacrylate) (PMMA) with epibromohydrin for the synthesis of well‐defined epoxy end‐functionalized polymers is reported. Polyanions were reacted with an excess of epibromohydrin in tetrahydrofuran (THF) at −78 °C. The functionalities of the resulting polymers were analyzed by matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS), NMR, and size exclusion chromatography (SEC). The epoxy end groups were reacted with 1,1‐diphenyl‐ hexyllithium, and MALDI‐TOF MS and NMR before and after this chemical modification were used to determine the presence of the epoxy end groups. The presence of the epoxy end group was confirmed by anionically polymerizing ethylene oxide from these epoxy end group. The formation of a block copolymer due to the epoxy end groups was proved by SEC analysis. The combined MALDI‐TOF MS, 1H NMR, and SEC results indicate that epoxy end‐capped PS was obtained in quantitative yield. The method was extended to the synthesis of epoxy end‐capped PMMA. With this polymer the extent of end‐functionalization was high but not quantitative, with non‐dimeric byproducts detected by MALDI‐TOF MS.magnified image
Poly(2,5‐thienylene vinylene) in Nano Shapes by CVD Polymerization
Authors: Lee Ki‐Ryong , Yu Young‐Jun , Joo Sung‐Hoon , Lee Chun‐Young , Choi Dong Hoon , Joo Jin Soo , Park Young‐Sup , Jin Jung‐Il 
Published: April 2007

AbstractPoly(2,5‐thienylene vinylene) (PTV), an insoluble conjugated polymer, can be readily prepared in various shapes of different nanodimensions by the chemical vapor deposition polymerization of 2,5‐bis(chloromethyl)thiophene. The bischloromethyl monomer in the vapor phase is activated at 600 °C. The activated monomer vapor is deposited at room temperature on the surface of various substrates to prepare polymeric films, fibers, tubes etc., which are then thermally converted into PTV. PTV thin films can be carbonized thermally to produce graphitic compositions that contain sulfur atoms. Electrical conductivities of FeCl‐doped PTV and carbonized films are reported.magnified image
Unusual Aggregation of Nanosized Six‐Arm Star Oligofluorenes
Authors: Han Yang , Fei Zhuping , Sun Minghao , Bo Zhishan , Liang Wan‐Zhen 
Published: April 2007

AbstractA series of monodisperse six‐arm benzene‐cored star oligofluorenes are prepared by a divergent/convergent strategy, starting from the repetitive divergent synthesis of symmetrical ethynyl‐bridged oligofluorenes to the convergent Co‐catalyzed alkyne cyclotrimerization. The structures of these six‐arm molecules are fully characterized. The diameter of the largest molecule SF3 reaches ca. 3 nm. These highly substituted star‐shaped oligomers exhibit extremely high fluorescent quantum yields in solution and unexpected red‐shifted and broadened emission with fine structure in the film as a result of the formation of stable aggregates.magnified image
Synthesis of Poly(methyl methacrylate) Nanoparticles Initiated by 2,2′‐Azoisobutyronitrile via Differential Microemulsion Polymerization
Authors: Norakankorn Chaiwat , Pan Qinmin , Rempel Garry L. , Kiatkamjornwong Suda 
Published: April 2007

AbstractThe synthesis of nanosized poly(methyl methacrylate) initiated by 2,2′‐azoisobutyronitrile via differential microemulsion polymerization has been investigated. Poly(methyl methacrylate) with a molecular weight of around 1 × 106 and a particle size of about 20 nm was achieved under mild reaction conditions. A typical condition was that the surfactant amount required could be as low as 1/130 of the monomer amount in weight, and the surfactant/water ratio could be as low as 1/600, which is much less than the corresponding amounts reported in the literature. “Molecular bricks”, i.e., nanoparticles in which there are only one or two polymer chains, can be achieved using mild conditions by differential microemulsion polymerization, which may have potential applications for making molecular devices.magnified image
Microporous Polymers as Potential Hydrogen Storage Materials
Authors: McKeown Neil B. , Budd Peter M. , Book David 
Published: April 2007

AbstractMicroporous organic polymers offer the possibility of storing hydrogen safely at low temperatures and moderate pressures via physisorption. A range of polymers of intrinsic microporosity (PIMs) have been studied. The best PIM to date is based on a triptycene monomer and takes up 2.7% H2 by mass at 10 bar/77 K. Hypercrosslinked polymers (HCPs) also show promising performance, particularly at pressures >10 bar. The form of the H2 isotherm is influenced by the micropore distribution, a higher concentration of ultramicropores (pore size <0.7 nm), as found in PIMs, being associated with enhanced low pressure adsorption. The performance of polymers relative to other microporous materials (carbons and metal‐organic frameworks) is compared and promising methods to enhance the hydrogen uptake of microporous polymers are suggested.magnified image
3T MR of the prostate: Reducing susceptibility gradients by inflating the endorectal coil with a barium sulfate suspension
Authors: Rosen Yael , Bloch B. Nicolas , Lenkinski Robert E. , Greenman Robert L. , Marquis Robert P. , Rofsky Neil M. 
Published: April 2007

AbstractMost prostate MRI/MRS examinations are performed with an endorectal coil inflated with air, leading to an air–tissue interface that induces magnetic susceptibility gradients within the gland. Inflation of the coil with a barium sulfate suspension is described and compared to inflation with air or liquid perfluorocarbon (PFC). The B0 field in the prostate gland was mapped for five healthy volunteers when the endorectal coil was inflated with each of the three agents. A marked decrease in the posterior‐anterior (P‐A) field gradient and a significant improvement in field homogeneity were evident in the presence of a barium suspension and PFC relative to air. MRS data acquired from the prostate gland in the presence of air, PFC, and a barium suspension in the endorectal coil showed similar trends, demonstrating improvement in line‐widths and spectral resolution when the barium suspension or the PFC were inflating the endorectal coil. On this basis we conclude that a barium suspension provides an available, cheap, and safe alternative to PFC, and we suggest that inflating the endorectal coil with a barium suspension should be considered for prostate MR studies, especially at high field strengths (such as 3T). Magn Reson Med 57:898–904, 2007. © 2007 Wiley‐Liss, Inc.
Optimal methods for the preservation of cartilage samples in MRI and correlative biochemical studies
Authors: Fishbein Kenneth W. , Canuto Holly C. , Bajaj Preeti , Camacho Nancy Pleshko , Spencer Richard G. 
Published: April 2007

AbstractMRI studies of cartilage require the prevention of sample degradation before and during scanning and during shipment for correlative studies. Methods to achieve this include immersion in protease inhibitors (PIs), refrigeration, and freezing. In this study, bovine nasal cartilage (BNC) samples were stored in Dulbecco's phosphate‐buffered saline (DPBS), DPBS with standard PIs, or PI solution with GM6001, a potent metalloproteinase inhibitor. For each buffer, three samples were scanned at +4°C and stored at +4°C or at −20°C with thawing prior to imaging. T2 and magnetization transfer (MT) rate, km, were measured weekly over 4 months, after which time water and glycosaminoglycan (GAG) contents were compared with those of matching tissue excised pre‐storage. Samples in DPBS exhibited increased T2 (+33.6% after 1 month at +4°C, P = 0.040) and decreased km (−20.6%, P = 0.004), while refrigeration in DPBS with PI and GM6001 yielded good stability (T2: +2.7%, P = 0.874; km: −4.2%, P = 0.654 after 108 days at +4°C). Water content increased while GAG content markedly decreased in all samples. Thus, stability in cartilage MRI parameters can be optimized with appropriate storage conditions, but storage time should nonetheless be minimized. Magn Reson Med 57:866–873, 2007. Published 2007 Wiley‐Liss, Inc.
Complex data analysis in high‐resolution SSFP fMRI
Authors: Lee Jongho , Shahram Morteza , Schwartzman Armin , Pauly John M. 
Published: April 2007

AbstractIn transition‐band steady‐state free precession (SSFP) functional MRI (fMRI), functional contrast originates from a bulk frequency shift induced by a deoxygenated hemoglobin concentration change in the activated brain regions. This frequency shift causes a magnitude and/or phase‐signal change depending on the off‐resonance distribution of a voxel in the balanced‐SSFP (bSSFP) profile. However, in early low‐resolution studies, only the magnitude signal activations were shown. In this paper the task‐correlated phase‐signal change is presented in a high‐resolution (1 × 1 × 1 mm3) study. To include this phase activation in a functional analysis, a new complex domain data analysis method is proposed. The results show statistically significant phase‐signal changes in a large number of voxels comparable to that of the magnitude‐activated voxels. The complex‐data analysis method successfully includes these phase activations in the activation map and thus provides wider coverage compared to magnitude‐data analysis results. Magn Reson Med 57:905–917, 2007. © 2007 Wiley‐Liss, Inc.
High‐resolution chemical shift imaging for the assessment of intramuscular lipids
Authors: Newcomer Bradley R. , Lawrence Jeannine C. , Buchthal Steven , den Hollander Jan A. 
Published: April 2007

AbstractA new high‐resolution MRSI technique was used to measure extracellular lipids (EMCL), intracellular lipids (IMCL), and total muscle lipids (TML). The purpose of this study was to assess the feasibility and reproducibility of this new technique. This study also compared results obtained from small regions of interest (ROIs) vs. a summation of a large ROI of voxels representing the total soleus or anterior tibialis (TA) muscles. Eight volunteers were studied with the use of a conventional single‐slice MR spectroscopic imaging (MRSI) sequence run with the following parameters: TR = 145.9 ms, FOV = 16 cm, slice thickness = 1 cm, and 64 × 64 phase encodes. EMCL, IMCL, and TML values from the small ROIs proved to be reproducible (coefficient of variation (CV) = 7.8–13.8% for soleus, and 8.2–18% for TA). EMCL, IMCL, and TML values from the larger soleus ROI proved to be reproducible (CV = 7.3–16.1%), whereas the larger TA ROIs were less reproducible. The small and larger soleus ROIs produced statistically equivalent measures of EMCL and TML per unit area. However, the small soleus and TA ROIs showed a trend toward yielding different IMCL contents as compared to the larger ROIs. This study demonstrates that high‐resolution 1H MRSI of the calf muscle is feasible and can reproducibly measure EMCL, IMCL, and TML. Magn Reson Med 57:848–858, 2007. © 2007 Wiley‐Liss, Inc.
T2‐prepared SSFP improves diagnostic confidence in edema imaging in acute myocardial infarction compared to turbo spin echo
Authors: Kellman Peter , Aletras Anthony H. , Mancini Christine , McVeigh Elliot R. , Arai Andrew E. 
Published: April 2007

AbstractT2‐weighted MRI of edema in acute myocardial infarction (MI) provides a means of differentiating acute and chronic MI, and assessing the area at risk of infarction. Conventional T2‐weighted imaging of edema uses a turbo spin‐echo (TSE) readout with dark‐blood preparation. Clinical applications of dark‐blood TSE methods can be limited by artifacts such as posterior wall signal loss due to through‐plane motion, and bright subendocardial artifacts due to stagnant blood. Single‐shot imaging with a T2‐prepared SSFP readout provides an alternative to dark‐blood TSE and may be conducted during free breathing. We hypothesized that T2‐prepared SSFP would be a more reliable method than dark‐blood TSE for imaging of edema in patients with MI. In patients with MI (22 acute and nine chronic MI cases), T2‐weighted imaging with both methods was performed prior to contrast administration and delayed‐enhancement imaging. The T2‐weighted images using TSE were nondiagnostic in three of 31 cases, while six additional cases rated as being of diagnostic quality yielded incorrect diagnoses. In all 31 cases the T2‐prepared SSFP images were rated as diagnostic quality, correctly differentiated acute or chronic MI, and correctly determined the coronary territory. Free‐breathing T2‐prepared SSFP provides T2‐weighted images of acute MI with fewer artifacts and better diagnostic accuracy than conventional dark‐blood TSE. Magn Reson Med 57:891–897, 2007. Published 2007 Wiley‐Liss, Inc.
Spectral phase‐corrected GRAPPA reconstruction of three‐dimensional echo‐planar spectroscopic imaging (3D‐EPSI)
Authors: Zhu Xiaoping , Ebel Andreas , Ji Jim X. , Schuff Norbert 
Published: April 2007

AbstractMR spectroscopic (MRS) images from a large volume of brain can be obtained using a 3D echo‐planar spectroscopic imaging (3D‐EPSI) sequence. However, routine applications of 3D‐EPSI are still limited by a long scan time. In this communication, a new approach termed “spectral phase‐corrected generalized autocalibrating partially parallel acquisitions” (SPC‐GRAPPA) is introduced for the reconstruction of 3D‐EPSI data to accelerate data acquisition while preserving the accuracy of quantitation of brain metabolites. In SPC‐GRAPPA, voxel‐by‐voxel spectral phase alignment between metabolite 3D‐EPSI from individual coil elements is performed in the frequency domain, utilizing the whole spectrum from interleaved water reference 3D‐EPSI for robust estimation of the zero‐order phase correction. The performance of SPC‐GRAPPA was compared with that of fully encoded 3D‐EPSI and conventional GRAPPA. Analysis of whole‐brain 3D‐EPSI data reconstructed by SPC‐GRAPPA demonstrates that SPC‐GRAPPA with an acceleration factor of 1.5 yields results very similar to those obtained by fully encoded 3D‐EPSI, and is more accurate than conventional GRAPPA. Magn Reson Med 57:815–820, 2007. © 2007 Wiley‐Liss, Inc.
Intuitive design guidelines for fast spin echo imaging with variable flip angle echo trains
Authors: Lebel R. Marc , Wilman Alan H. 
Published: April 2007

AbstractWe present a simple and intuitive means for determining the flip angles (FAs) required for smooth transitions between static pseudo steady states (SPSSs) in fast spin echo (FSE) imaging with variable FA (VFA) echo trains. We demonstrate the effectiveness of single and multiple transition pulses to successfully vary refocusing FAs while retaining high signal levels. The graphical interpretation presented here is consistent with previous analytical techniques and permits accurate signal‐intensity predictions along the echo train. Magn Reson Med 57:972–975, 2007. © 2007 Wiley‐Liss, Inc.
Self‐calibrated GRAPPA method for 2D and 3D radial data
Authors: Arunachalam Arjun , Samsonov Alexey , Block Walter F. 
Published: April 2007

AbstractA fast parallel MRI (pMRI) reconstruction method is presented for 2D and 3D radial trajectories. A limitation of the radial generalized autocalibrating partially parallel acquisitions (GRAPPA) method is the need to acquire training data prior to the actual scan. This can be eliminated by the use of self‐calibration when synthesizing the missing data for each coil reconstruction. The training data for each coil are estimated by multiplying the conventionally reconstructed composite image, which contains the aliasing artifacts from undersampling, with each coil's spatial sensitivity profile. An estimate of the individual receiver spatial sensitivity profiles is obtained from the k‐space data that fulfill the Nyquist sampling criterion. The frequency domain representation of the training data is then calculated at the acquired k‐space sample points and at the unacquired locations at which we desire to synthesize k‐space data. Fitting the acquired k‐space samples to the unacquired points creates reconstruction weights that are used to synthesize unacquired radial lines. The in vivo feasibility of the method for 2D radial trajectories is illustrated with an example of 2D abdominal imaging. Preliminary results obtained after applying the method on a 3D radial steady‐state free precession (SSFP) data set are also demonstrated. Magn Reson Med 57:931–938, 2007. © 2007 Wiley‐Liss, Inc.
Fast mapping of the T2 relaxation time of cerebral metabolites using proton echo‐planar spectroscopic imaging (PEPSI)
Authors: Tsai Shang‐Yueh , Posse Stefan , Lin Yi‐Ru , Ko Cheng‐Wen , Otazo Ricardo , Chung Hsiao‐Wen , Lin Fa‐Hsuan 
Published: April 2007

AbstractMetabolite T2 is necessary for accurate quantification of the absolute concentration of metabolites using long‐echo‐time (TE) acquisition schemes. However, lengthy data acquisition times pose a major challenge to mapping metabolite T2. In this study we used proton echo‐planar spectroscopic imaging (PEPSI) at 3T to obtain fast T2 maps of three major cerebral metabolites: N‐acetyl‐aspartate (NAA), creatine (Cre), and choline (Cho). We showed that PEPSI spectra matched T2 values obtained using single‐voxel spectroscopy (SVS). Data acquisition for 2D metabolite maps with a voxel volume of 0.95 ml (32 × 32 image matrix) can be completed in 25 min using five TEs and eight averages. A sufficient spectral signal‐to‐noise ratio (SNR) for T2 estimation was validated by high Pearson's correlation coefficients between logarithmic MR signals and TEs (R2 = 0.98, 0.97, and 0.95 for NAA, Cre, and Cho, respectively). In agreement with previous studies, we found that the T2 values of NAA, but not Cre and Cho, were significantly different between gray matter (GM) and white matter (WM; P < 0.001). The difference between the T2 estimates of the PEPSI and SVS scans was less than 9%. Consistent spatial distributions of T2 were found in six healthy subjects, and disagreement among subjects was less than 10%. In summary, the PEPSI technique is a robust method to obtain fast mapping of metabolite T2. Magn Reson Med 57:859–865, 2007. © 2007 Wiley‐Liss, Inc.
Contrast‐enhanced MRI of right ventricular abnormalities in Cx43 mutant mouse embryos
Authors: Wadghiri Youssef Zaim , Schneider Amanda E. , Gray Emily N. , Aristizabal Orlando , Berrios Cesar , Turnbull Daniel H. , Gutstein David E. 
Published: April 2007

AbstractImaging of the mammalian cardiac right ventricle (RV) is particularly challenging, especially when a two‐dimensional method such as conventional histology is used to evaluate the morphology of this asymmetric, crescent‐shaped chamber. MRI may improve the characterization of mutants with RV phenotypes by allowing analysis of the samples in any plane and by facilitating three‐dimensional image reconstruction. MRI was used to examine the conditional knockout Cx43‐PCKO mouse line known to have RV malformations. To help delineate the cardiovascular system and facilitate identification of the right ventricular outflow tract (RVOT), embryonic day (E) 17.5 embryos were perfusion fixed through the umbilical vein followed by a gadolinium‐based contrast agent mixed in 7% gelatin. Micro‐MRI experiments were performed at 7 T and followed by paraffin embedding of specimens, histological sectioning and hematoxylin and eosin (H&E) staining. Imaging of up to four embryos simultaneously allowed for higher throughput than traditional individual imaging techniques, while intravascular contrast afforded excellent signal‐to‐noise characteristics. All control embryos (n = 4) and heterozygous Cx43 knockout embryos (n = 4) had normal‐appearing right ventricular outflow tract contours by MRI. Obvious abnormalities in the RVOT, including abnormal bulging and infiltration of contrast into the wall of the RV, were seen in three out of four Cx43‐PCKO mutants with MRI. Furthermore, three‐dimensional reconstruction of MR images with orthogonal projections as well as maximum‐intensity projection allowed for visualization of the relationship of infundibular bulging segments to the pulmonary trunk in Cx43‐PCKO mutant hearts. The addition of MRI to standard histology in the characterization of RV malformations in mutant mouse embryos aids in the assessment and understanding of morphologic abnormalities. Flexibility in the viewing of MR images, which can be retrospectively sectioned in any desired orientation, is particularly useful in the investigation of the RV, an asymmetric chamber that is difficult to analyze with two‐dimensional techniques. Copyright © 2007 John Wiley & Sons, Ltd.
Measurement of nonlinear pO2 decay in mouse lungs using 3He‐MRI
Authors: Cieślar Katarzyna , Alsaid Hasan , Stupar Vasile , Gaillard Sophie , Canet‐Soulas Emmanuelle , Fissoune Rachida , Crémillieux Yannick 
Published: April 2007

AbstractSpatial and temporal variations in oxygen partial pressure (pO2) during breath‐hold can be exploited to obtain important regional parameters of lung function. In the course of apnea, the oxygen concentration is known to decay exponentially. Therefore, the initial pO2 (p0) can be used to represent local ventilation, and the oxygen depletion time constant can characterize perfusion. The protocol, based on a nonlinear model of pO2 decay, was validated in six healthy mice. Parametric maps of p0 and oxygen depletion time constant were obtained for pure 3He and 3He/air mixture. The mean measured values of p0 were 77 ± 9 mbar for the pure 3He insufflation and 107 ± 5 mbar for 3He/air mixture, in agreement with the predefined p0 values: 75 ± 15 mbar and 123 ± 15 mbar, respectively. The mean measured oxygen depletion time constants were 6.5 ± 0.2 s for pure 3He and 7.1 ± 0.8 s for the 3He/air mixture, in agreement with physiology. Copyright © 2007 John Wiley & Sons, Ltd.