bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Development of Stereoerrors During the Homo‐ and Copolymerization of Propylene Using C2‐Symmetric Metallocene Catalysts – A Cautionary Note
Authors: van Reenen Albert J. , Lutz Marietjie 
Published: August 2004

AbstractSummary: A recent paper described the development of atactic sequences during the copolymerization of propylene and 1‐pentene using the C2‐symmetric metallocene catalyst rac‐dimethylsilyl‐bis(2‐methylbenz(e)indenyl) zirconium dichloride. We have found similar stereoerrors, and showed that atactic material could in fact be extracted from the material, indicating that the catalyst in question had probably isomerized in solution, leading to a mixture of isotactic and atactic polymers.
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Phase Composition and Molecular Mobility in Nylon 6 Fibers as Studied by Proton NMR Transverse Magnetization Relaxation
Authors: Litvinov Victor M. , Penning Jan Paul 
Published: August 2004

AbstractSummary: The phase composition and molecular mobility of Nylon 6 fibers has been studied using 1H solid‐state NMR transverse magnetization relaxation (T2 relaxation) spectroscopy. One of the objectives of this work is to determine the usefulness of the NMR relaxation method to accurately determine the crystallinity of Nylon 6 fibers. The NMR relaxation results have been interpreted using a three‐phase model, which is proposed on the basis of distinct differences in chain mobility in the crystalline phase, the semi‐rigid crystal‐amorphous interface, and the soft amorphous phase. In order to obtain accurate data on the phase composition, the effects of absorbed water and annealing of fibers at elevated temperatures were studied in detail. It was shown that water mainly plasticizes the soft fraction of the amorphous phase. Changes in the phase composition and molecular mobility caused by fiber annealing at elevated temperatures were studied with real‐time NMR T2 relaxation experiments. The most pronounced annealing effects (changes in the phase composition) were observed for undrawn fibers with low molecular orientation. Annealing slows down for fibers produced at larger winding speed and especially those with a high draw ratio. Fiber processing conditions, i.e., winding speed and draw ratio, are found to affect the phase composition and molecular mobility in different phases. It was shown that the present NMR relaxation method provides a fast and accurate technique to analyze the phase composition of Nylon 6 fibers. The amount of rigid phase determined from NMR is in good agreement with the crystallinity of the fiber obtained using the traditional method for Nylon 6 fibers, which involves a combination of density measurement, wide‐angle X‐ray diffraction and 13C NMR spectroscopy. Hence, the present NMR relaxation method greatly simplifies measurement of crystallinity in Nylon 6 fibers.The effect of draw ratio on the phase composition in Nylon 6 fibers as studied by NMR and the traditional method.magnified imageThe effect of draw ratio on the phase composition in Nylon 6 fibers as studied by NMR and the traditional method.
Diblock Copolymers Based on 1,4‐Dioxan‐2‐one and ε‐Caprolactone: Characterization and Thermal Properties
Authors: Raquez Jean‐Marie , Degée Philippe , Narayan Ramani , Dubois Philippe 
Published: August 2004

AbstractSummary: Various poly(ε‐caprolactone‐block‐1,4‐dioxan‐2‐one) (P(CL‐block‐PDX)) block copolymers were prepared according to the living/controlled ring‐opening polymerization (ROP) of 1,4‐dioxan‐2‐one (PDX) as initiated by in situ generated ω‐aluminium alkoxides poly(ε‐caprolactone) (PCL) chains in toluene at 25 °C.1 1H NMR, PCS and TEM measurements have attested for the formation of colloids attributed to a growing PPDX core surrounded by a solvating PCL shell during the polymerization of PDX promoted by ω‐Al alkoxide PCL chains in toluene. The thermal behavior of the P(CL‐block‐PDX) copolymers was studied by DSC; showing two distinct melting temperatures (as well as two glass transition temperatures) similar to those of the respective homopolyesters. Finally, the thermal degradation of the P(CL‐block‐PDX) block copolymers was investigated by TGA simultaneously coupled to a FT‐IR spectrometer and a mass spectrometer for evolved gas analysis (EGA). The degradation occurred in two consecutive steps involving a first unzipping depolymerization of the PPDX blocks followed by the degradation of the PCL blocks via both ester pyrolysis and unzipping reactions.TEM observation of P(CL‐block‐PDX) block copolyesters ($\overline M _{{\rm nPCL}}$ = 11 600 and $\overline M _{{\rm nPPDX}}$ = 22 100) as formed by vaporization starting from a diluted suspension in toluene/TCE mixture solvent (50/50 v/v).magnified imageTEM observation of P(CL‐block‐PDX) block copolyesters ($\overline M _{{\rm nPCL}}$ = 11 600 and $\overline M _{{\rm nPPDX}}$ = 22 100) as formed by vaporization starting from a diluted suspension in toluene/TCE mixture solvent (50/50 v/v).
Synthesis and Characterization of Polymer Brushes on Micromechanical Cantilevers
Authors: Bumbu Gina‐Gabriela , Kircher Gunnar , Wolkenhauer Markus , Berger Rüdiger , Gutmann Jochen S. 
Published: August 2004

AbstractSummary: A technique to cover microelectromechanical systems (MEMS), such as micromechanical cantilever (MC) sensors, with a covalently bound brush layer has been developed. The polymer layer was grown using a “grafting‐from” synthesis of polymer brushes under mild conditions, by surface‐initiated atom transfer radical polymerization. Atomic force microscopy (AFM) and ellipsometry have revealed a uniform thickness of about 12 nm from which a grafting density of polymer brushes of 0.19 chains · nm−2 was estimated. The coating with polymer brushes can be realized on a selected surface. It was shown that a single‐sided brush layer swells reversibly in toluene, resulting in a bending of the micromechanical cantilever.Schematic representation of the PMMA brush synthesis on the MC surface, by surface‐initiated ATRP.magnified imageSchematic representation of the PMMA brush synthesis on the MC surface, by surface‐initiated ATRP.
Cover Picture: Macromol. Chem. Phys. 12/2004
Authors: Kitano Hiromi , Hirabayashi Tadashi , Gemmei‐Ide Makoto , Kyogoku Mayumi 
Published: August 2004

Front Cover: The picture on the cover shows the coil‐globule transition of the graft polymer with increasing temperature, and the change of lower critical solution temperature (LCST) upon the formation of polypseudorotaxane of grafted poly(ethylene glycol) with sulfonated calixarene. It can be understood well from this graphics that the LCST of the graft polymer significantly changes due to the formation of polypseudorotaxane (blue broken line: graft polymer solution, wine red broken line: graft polymer‐calixarene mixture).Further details can be found in the Full Paper by H. Kitano,* T. Hirabayashi, M. Gemmei‐Ide, and M. Kyogoku on page 1651.
Gelation Studies: Comparison of the Critical Exponents Obtained by Dynamic Light Scattering and Rheology, 2
Authors: Richter Sven , Boyko Volodymyr , Matzker Rolf , Schröter Klaus 
Published: August 2004

AbstractSummary:The sol–gel transition of two thermoreversible gelling mixtures made of xanthan gum and locust‐bean gum has been studied by using in situ, time‐resolved dynamic light scattering (DLS) and in situ rheology. A critical dynamical behavior was observed near the sol–gel transition, which was characterized by the presence of power‐law spectra over three and four decades in the time‐intensity correlation functiong2(t) − 1 ∼ t−μand over four and three decades in the oscillatory shear experimentG′(ω) ∼ G″(ω) ∼ ωn. A comparison of the critical exponents obtained (μ1 ≈ 0.36, μ2 ≈ 0.32 andn1 ≈ 0.62,n2 ≈ 0.67) was made as a function of the dependence of the two mixing ratios according to the theory by Doi and Onuki. New experiments were also performed to compare the critical exponents on such a thermoreversible system.Double‐logarithmic plot of the time‐intensity correlation functionsg2(t) − 1 versus the delay time,t, at a 90° scattering angle and at several temperatures of the mixture 1.imageDouble‐logarithmic plot of the time‐intensity correlation functionsg2(t) − 1 versus the delay time,t, at a 90° scattering angle and at several temperatures of the mixture 1.
Accurate mass measurements by Fourier transform mass spectrometry
Authors: Zhang Li‐Kang , Rempel Don , Pramanik Birendra N. , Gross Michael L. 
Published: August 2004

AbstractThe capability for accurate mass measurements is an important attribute of Fourier transform mass spectrometry (FTMS). Unlike other instrumental methods in mass spectrometry, FTMS still offers significant opportunities to improve mass measurement accuracy (MMA), making it an area of research. This review covers the published literature in FTMS from the late 1970s to the present. We discuss the development and evolution of mass calibration that give accuracies in the low ppm range. We sketch the derivation and show the common foundation of these mass calibration procedures. We also describe the relation of mass calibration and the fundamentals of ion motion and space‐charge effects, and we review efforts to improve the basic calibration procedure particularly those that correct for effects of space charge. The advent of matrix‐assisted laser desorption ionization (MALDI) and electrospray ionization (ESI) have opened the door for FTMS to be used for analyzing at high performance biopolymers, including proteins, oligodeoxynucleotides (ODNs), oligosaccharides, and synthetic polymers. We also discuss the utility of FTMS for accurate mass measurement in these areas and some practical ways to improve MMA. © 2004 Wiley Periodicals, Inc., Mass Spec Rev 24:286–309, 2005
A novel family with an unusual early‐onset generalized dystonia
Authors: Fabbrini Giovanni , Brancati Francesco , Vacca Laura , Valente Enza Maria , Nemeth Andrea , Meesaq Angela , Sykes Nuala , Dallapiccola Bruno , Berardelli Alfredo 
Published: August 2004

AbstractWe report on an Italian family in which three brothers and their maternal grandfather had a generalized early‐onset dystonia with mild parkinsonian signs. Genetic testing excluded the rapid‐onset dystonia‐parkinsonism locus (DYT12; OMIM*128235), autosomal recessive Parkin locus (PARK2; OMIM *602544), and DYT1 dystonia. Three affected siblings were found to share an identical haplotype at the X‐linked dystonia–parkinsonism locus (XDP; Lubag; OMIM*314250). This haplotype differed from the haplotype observed in Filipino patients, ruling out the hypothesis of a common underlying mutation. In addition, direct sequencing analysis of the putative disease causing changes observed in Filipino patients were not found in the Italian patients. The condition we describe could be a newly recognized dystonia syndrome with parkinsonism. © 2004 Movement Disorder Society
Chewing pattern in patients with Meige's syndrome
Authors: Mascia Marcello M. , Valls‐Solé Josep , Martí Maria J. , Sanz Sergio 
Published: August 2004

AbstractMeige's syndrome presents with a combination of upper and lower facial motor dysfunction, including eye closing spasms and oromandibular dystonia. While the pathophysiology of eye closing spasms has been extensively studied using the blink reflex and other trigeminofacial reflexes, very few studies have been carried out with regard to the abnormal perioral movements. We hypothesized that action‐related dystonic features could be revealed by the analysis of the semiautomatic rhythmic movements required for chewing and swallowing. A total of 7 patients with Meige's syndrome that complained of chewing problems and 7 age‐matched healthy volunteers were studied. Subjects were instructed to munch and swallow a small muffin while surface electromyographic (EMG) activity of masseter (MAS) and orbicularis oris (OOr) of the dominant side was recorded. In healthy subjects, MAS and OOr showed a rhythmic alternating phasic EMG pattern during chewing, which changed to a tonic cocontraction of both muscles during swallowing. Mean duration of MAS and OOr EMG bursts was, respectively, 297 ± 28 msec and 328 ± 29 msec. Patients exhibited the following alterations: excess duration of muscle activity, frequent cocontraction, loss of rhythmicity during chewing, and abnormalities in the chewing to swallowing transition phase. These abnormalities, similar in type to those encountered in other forms of focal dystonia, may be the expression of an abnormal motor control of basal ganglia over mastication‐related movement pattern generators of the brainstem. © 2004 Movement Disorder Society
Left hemibody myoclonus due to anomalous right vertebral artery
Authors: Coelho Miguel , Marti Maria J. , Valls‐Solé Josep , Pujol Teresa , Tolosa Eduardo 
Published: August 2004

AbstractA 43‐year‐old man presented with sporadic, sudden, brief, and involuntary jerks of his left limbs and trunk muscles. The electromyographic recordings showed short‐lasting highly synchronized bursts, compatible with myoclonus limited to the left hemibody. Blink reflex, masseter silent period, cortical and spinal magnetic stimulation, somatosensory cortical evoked potentials, and electroencephalogram (EEG) were normal; the EEG back‐averaging showed no spikes preceding the myoclonus. Magnetic resonance imaging and magnetic resonance angiography showed the presence of an anomalous nonectasic right vertebral artery compressing the right side of ventral medulla oblongata. We hypothesize that the aberrant right vertebral artery induced abnormal activation of descending motor tracts responsible for the myoclonus. © 2004 Movement Disorder Society
Dyskinesias due to intravenous apomorphine abuse in a patient without basal ganglia disorder
Authors: Happe Svenja , Sommer Martin , Meller Johannes , Trenkwalder Claudia , Paulus Walter 
Published: August 2004

AbstractDyskinesias are known to occur in many patients with Parkinson's disease treated with dopaminergic drugs but to date, drug‐induced dyskinesias have not been observed in humans with no underlying basal ganglia disorder. We describe a patient with psychogenic parkinsonism and intravenous apomorphine abuse leading to subsequent choreatiform dyskinesias. © 2004 Movement Disorder Society
13C and 1H nuclear magnetic resonance of methyl‐substituted acetophenones and methyl benzoates: steric hindrance and inhibited conjugation
Authors: Buděšínský Miloš , Kulhánek Jiří , Böhm Stanislav , Cigler Petr , Exner Otto 
Published: August 2004

AbstractThe 1H and 13C NMR spectra of 14 methyl‐substituted acetophenones and 14 methyl‐substituted methyl benzoates were assigned and interpreted with respect to the conformation of the Car—C(O) bond. The substituent effects are proportional in the two series and can be divided into polar and steric: each has different effects on the 13C SCS of the individual atoms. In the case of C atoms C(O), C(1) and CH3(CO), the steric effects were quantitatively separated by comparing SCS in the ortho and para positions. The steric effects are proportional for the individual C atoms and also to steric effects estimated from other physical quantities. However, they do not depend simply on the angle of torsion ϕ of the functional group as anticipated hitherto. A better description distinguishes two classes of compounds: sterically not hindered or slightly hindered planar molecules and strongly sterically hindered, markedly non‐planar. In order to confirm this reasoning without empirical correlations, the J(C,C) coupling constants were measured for three acetophenone derivatives labeled with 13C in the acetyl methyl group. The constants confirm unambiguously the conformation of 2‐methylacetophenone; their zero values are in accord with the conformation of 2,6‐dimethylacetophenone. The zero values in the unsubstituted acetophenone are at variance with previous erroneous report but all J(C,C) values are in accord with calculations at the B3LYP/6‐311++G(2d,2p)//B3LYP/6–311+G(d,p) level. Copyright © 2004 John Wiley & Sons, Ltd.
An experimental and theoretical study of the Cp2VO2CO: use of 13CO32− for structure investigation of d1‐metallocene complexes
Authors: Vinklárek Jaromír , Honzíček Jan , Holubová Jana 
Published: August 2004

AbstractEPR study has shown that the anticancer agent vanadocene dichloride (Cp2VCl2) interacts with carbonate contained in physiological solutions. Chelate complex Cp2VO2CO (|Aiso(51V)| = 175.1 MHz, giso = 1.9861) is the only paramagnetic species formed in the range about the physiological pH (5.5–11.0). The super‐hyperfine coupling (|aiso(13C)| = 24.1 MHz) was evidenced at measurements using 13C labelled carbonate. The structure of carbonate complex was validated by comparison of observed and theoretical calculated HFC tensors (at the density functional level of theory). Copyright © 2004 John Wiley & Sons, Ltd.
Electron spin resonance study of phosphorus‐nitroxides from 1,3‐additions of silicon‐phosphorus reagents to nitrones
Authors: Haire D. Lawrence , Janzen Edward G. , Robinson Valerie J. , Hrvoic Ivan 
Published: August 2004

AbstractThis article explores a new, convenient route to β‐phosphorus nitroxides. Specifically, the reaction sequence involves the novel 1,3‐addition of trimethylsilyl phosphites (e.g. diethyl) or trimethylsilyl phosphines (e.g. diphenyl) to aldo‐nitrones [e.g. α‐phenyl‐N‐tert‐butylnitrone (PBN) or 5,5‐dimethyl‐l‐pyrroline‐N‐oxide (DMPO)] or keto‐nitrones [e.g. 2‐ethyl‐5,5‐dimethyl‐1 pyrroline‐N‐oxide (2‐Et‐DMPO) or 2‐phenyl‐5,5‐dimethyl‐l‐pyrroline‐N‐oxide (2‐Ph‐DMPO)] to form α‐phosphityl‐ or α‐phosphinyl‐O‐silylhydroxylamines. Acidic hydrolysis provides the corresponding hydroxylamines that are easily oxidized to the title β‐phosphorus‐nitroxides. ESR spectroscopic analysis revealed some very large β‐phosphorus hyperfine splittings (i.e. in excess of 5 mT). For this reason and their remarkable stability (persistence) some of these nitroxides show promise as integral components in new, improved weak‐field dynamic nuclear polarization (DNP) magnetometers. Copyright © 2004 John Wiley & Sons, Ltd.
Conformational evaluation and detailed 1H and 13C NMR assignments of eremophilanolides
Authors: Burgueño‐Tapia Eleuterio , Hernández Luis R. , Reséndiz‐Villalobos Adriana Y. , Joseph‐Nathan Pedro 
Published: August 2004

AbstractExtensive application of 1D and 2D NMR methodology, combined with molecular modeling, allowed the complete 1H and 13C NMR assignments of eremophilanolides from Senecio toluccanus. Comparison of the experimental 1H, 1H coupling constant values with those generated employing a generalized Karplus‐type relationship, using dihedral angles extracted from MMX and DFT calculations, revealed that the epoxidized eremophilanolides 1 and 2 show conformational rigidity at room temperature, whereas molecules 3–6, containing an isolated double bond, are conformationally mobile. Copyright © 2004 John Wiley & Sons, Ltd.
13C CP/MAS NMR studies of vitamin E model compounds
Authors: Witkowski Stanislaw , Paradowska Katarzyna , Wawer Iwona 
Published: August 2004

Abstract13C cross‐polarization magic angle spinning (CP/MAS) NMR data for 2,2,5,7,8‐pentamethylchroman‐6‐ol (2), 6‐hydroxy‐2,5,7,8‐tetramethylchroman‐2‐carboxylic acid (Trolox c) (3) and its acetate (4), 2‐methoxy‐2,2,5,7,8‐pentamethylchroman‐6‐ol (5), 2‐hydroxy‐2,2,5,7,8‐pentamethylchroman‐6‐ol (6) and 2,2,5,7,8‐pentamethylchroman (7) are reported. A deshielding of 7.7 ppm for the carboxylic carbon was observed in solid Trolox due to formation of intermolecular hydrogen bonds within cyclic dimers. Such crystal packing permits effective cross‐polarization and fast relaxation (short T1ρH). The impact of the proton concentration on the CP dynamics is reflected by the longer TCP and T1ρH for Trolox‐d2 (deuterated at mobile proton sites). The calculated GIAO RHF shielding constants are sensitive to intramolecular effects: rotation around the C‐6O bond (changes of σ up to 8 ppm) and conformation at C‐2. Copyright © 2004 John Wiley & Sons, Ltd.
Exact likelihood inference for the exponential distribution under generalized Type‐I and Type‐II hybrid censoring
Authors: Chandrasekar B. , Childs A. , Balakrishnan N. 
Published: August 2004

AbstractChen and Bhattacharyya [Exact confidence bounds for an exponential parameter under hybrid censoring, Commun Statist Theory Methods 17 (1988), 1857–1870] considered a hybrid censoring scheme and obtained the exact distribution of the maximum likelihood estimator of the mean of an exponential distribution along with an exact lower confidence bound. Childs et al. [Exact likelihood inference based on Type‐I and Type‐II hybrid censored samples from the exponential distribution, Ann Inst Statist Math 55 (2003), 319–330] recently derived an alternative simpler expression for the distribution of the MLE. These authors also proposed a new hybrid censoring scheme and derived similar results for the exponential model. In this paper, we propose two generalized hybrid censoring schemes which have some advantages over the hybrid censoring schemes already discussed in the literature. We then derive the exact distribution of the maximum likelihood estimator as well as exact confidence intervals for the mean of the exponential distribution under these generalized hybrid censoring schemes. © 2004 Wiley Periodicals, Inc. Naval Research Logistics, 2004
Trade‐offs on the location of the core node in a network
Authors: Macq Jean‐François , Goemans Michel X. 
Published: August 2004

AbstractWe consider the problem of selecting a core node in a network under two potentially competing criteria, one being the sum of the distances to a set of terminals, the other being the cost of connecting this core node and the terminals with a Steiner tree. We characterize the worst‐case trade‐off between approximation ratios for the two objectives. Our results, for example, show the existence of a core node in which both objectives are simultaneously within 1.37 times their optimum value (if we were to disregard the other objective). We also consider the problem of minimizing a weighted sum of the two criteria and perform a worst‐case analysis of a simple and fast heuristic, which does not need to enumerate possible core locations. This study was motivated by multimedia applications such as videoconferences or multiplayer games in which user‐dependent information has to be sent from the users to a core node to be chosen (at a cost proportional to the sum of the distances from the core node), and then global information has to be multicast back from the core node to all users (at a cost proportional to the Steiner tree cost). © 2004 Wiley Periodicals, Inc. NETWORKS, Vol. 44(3), 179–186 2004
The ring grooming problem
Authors: Chow Timothy Y. , Lin Philip J. 
Published: August 2004

AbstractThe problem of minimizing the number of bidirectional SONET rings required to support a given traffic demand has been studied by several researchers. Here we study the relatedring‐groomingproblem of minimizing the number of add/drop locations instead of the number of rings; in a number of situations this is a better approximation to the true equipment cost. Our main result is a new lower bound for the case of uniform traffic. This allows us to prove that a certain simple algorithm for uniform traffic is, in fact, a constant‐factor approximation algorithm, and it also demonstrates that known lower bounds for the general problem—in particular, the linear programming relaxation—are not within a constant factor of the optimum. We also show that our results for uniform traffic extend readily to the more practically important case of quasi‐uniform traffic. Finally, we show that if the number of nodes on the ring is fixed, then ring grooming is solvable in polynomial time; however, whether ring grooming is fixed‐parameter tractable is still an open question. © 2004 Wiley Periodicals, Inc. NETWORKS, Vol. 44(3), 194–202 2004