bluuebunny/crossref_metadata_2025_split huggingface dataset:
In‐Line Monitoring and Control of Conversion and Weight‐Average Molecular Weight of Polyurethanes in Solution Step‐Growth Polymerization Based on Near Infrared Spectroscopy and Torquemetry
Authors: Nogueira Evandro S. , Borges Cristiano P. , Pinto José C. 
Published: April 2005

AbstractSummary: It is well known that the weight‐average molecular weight ($\overline M _{\rm w}$) is strictly dependent on conversion in step‐growth polymerizations performed in batch and that the $\overline M _{\rm w}$ is very sensitive to impurities and molar imbalance. This makes the work of controlling $\overline M _{\rm w}$ a non trivial job. In this paper a new methodology is introduced for in‐line monitoring and control of conversion and $\overline M _{\rm w}$ of polyurethanes produced in solution step‐growth polymerizations, based on near‐infrared spectroscopy (NIRS) and torquemetry. A calibration model based on the PLS method is obtained and validated for monomer conversion, while the weight‐average molecular weight is monitored indirectly with the relative shear signal provided by the agitator. Control procedures are then proposed and implemented experimentally to avoid gelation and allow for maximization of $\overline M _{\rm w}$. The proposed monitoring and control procedures can also be applied to other step growth polymerizations.Proposed control scheme.magnified imageProposed control scheme.
Steady‐State Model for Olefin Polymerization With a Two‐Site Vanadium Catalyst in a Continuous Stirred‐Tank Reactor
Authors: D'Agnillo Luigi , Soares Joao B. P. , van Doremaele Gerard H. J. 
Published: April 2005

AbstractSummary: In this study, a process for continuous EP(D)M production is examined and a mechanistic kinetic model is developed to explain the behavior exhibited by this vanadium‐catalyzed solution polymerization process. The catalyst system without promoter and without hydrogen, produces polymer with bimodal molecular weight distributions (MWDs), while the addition of catalyst promoter causes an order of magnitude increase in catalyst productivity and eliminates the higher‐MW component in the MWD. The addition of hydrogen also precludes bimodal MWDs, regardless of the presence of promoter. In all cases, the polymerization rate has a zero‐order rather than a first‐order response to monomer concentration. The zero‐order response of polymerization rate to monomer concentration is described using a mechanism of monomer coordination to form a stable complex prior to insertion. The bimodal MWDs at high monomer feeds (corresponding to low monomer conversion), in the absence of catalyst promoter and hydrogen, are explained by a two‐site type catalyst model in which both monomer insertion and the formation of the second‐site type occur after the monomer forms a stable coordinated complex with the first catalyst site type. The model reconciles the molecular weight development with these seldom‐discussed features of vanadium catalysis.Propylene acting as a coordinating ligand at a coordinatively unsaturated vanadium catalyst site (adapted from ref.[7]).magnified imagePropylene acting as a coordinating ligand at a coordinatively unsaturated vanadium catalyst site (adapted from ref.[7]).
Trunk sway in patients with spinocerebellar ataxia
Authors: Van de Warrenburg Bart P.C. , Bakker Maaike , Kremer Berry P.H. , Bloem Bastiaan R. , Allum John H.J. 
Published: April 2005

AbstractWe investigated whether quantified measurements of trunk sway during stance and gait tests in patients with autosomal dominant spinocerebellar ataxia (SCA) could be a useful approach to assess ataxia, which is highly relevant for adequate follow‐up and future intervention studies. Examined were 11 SCA patients and 11 age‐matched, healthy controls. Postural and balance control were quantified using peak‐to‐peak measurements of trunk angle and angular velocity, in the roll (lateral) and pitch (anterior–posterior) directions, during a battery of stance and gait tasks. In all stance tasks, trunk angle displacement and angular velocity in both the pitch and roll planes were significantly larger in the SCA group compared with the control group. Among the ataxia patients instability was more increased in the pitch than in the roll direction for two‐legged stance tasks, especially when standing on foam, with pronounced oscillations in the pitch plane at 1.4 and 2.5 Hz. A similar dominance of pitch over roll instability was also observed in most gait tasks, especially for tandem gait and while walking with simultaneous head rotations. Trunk sway measurements were effective in detecting and quantifying the gait and balance abnormalities in SCA patients, suggesting that this method might be used for follow‐up studies of SCA patients. Furthermore, the method might help to identify early symptomatic individuals and those patients at risk of falling. The postural instability in SCA was found to be multidirectional, although there is generally more pitch than roll instability corresponding with predominant involvement of the spinocerebellum. © 2005 Movement Disorder Society
Block‐row Hankel weighted low rank approximation
Authors: Schuermans M. , Lemmerling P. , Van Huffel S. 
Published: April 2005

AbstractThis paper extends the weighted low rank approximation (WLRA) approach to linearly structured matrices. In the case of Hankel matrices with a special block structure, an equivalent unconstrained optimization problem is derived and an algorithm for solving it is proposed. Copyright © 2005 John Wiley & Sons, Ltd.
On the convergence of the multi‐point flux approximation O‐method: Numerical experiments for discontinuous permeability
Authors: Eigestad G. T. , Klausen R. A. 
Published: April 2005

AbstractThis article presents numerical convergence results for the multi‐point flux approximation (MPFA) O‐method applied to the pressure equation in 2D. The discretization is made directly in physical space, and the investigated cases are simulated on structured, but generally skew grids. Skew grids need to be used to correctly represent the physics of the underlying flow problems. Special emphasis is made on cases which impose singularities in the velocity field. Such cases frequently arise in the description of subsurface flow. Analytical tools may not be applicable to fully answer the question of convergence for such cases; in particular not for the physical space discretization. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2005
Caribbean electricity restructuring: an assessment
Authors: Brewster Ancile 
Published: April 2005

AbstractThis article assesses the privatisation of the electricity sector in two Caribbean countries, Jamaica and Trinidad and Tobago, to determine if they have been successful and whether they have contributed benefits to the respective societies.Two general methods are applied in assessing the success of the divestments; attainment of governments' stated objectives and commonly used utility performance metrics together with social and customer focus indicators. The results indicate that the stated objectives were broadly achieved, and the privatisation and its attempts brought benefits to the consumers and the society in general. The short to medium term benefits were accrued through lower labour costs per unit of electricity, higher performance of plant and operations and business led decision‐making. Long‐term benefits are accrued through the reduction or elimination of electricity supply deficits.However, although the basic privatisations were successful, the absence of an adequate regulatory framework in one case may have reduced the quantum of benefits through failure to enforce continuous improvement in the privatised generation company, and reductions in worker rents in the public distribution company. Further, benefits were reduced by long divestment processes, accompanying strategic drift, opportunity costs from delayed sale proceeds and efficiency enhancement, and the costs to sustain interim operations. Copyright © 2005 John Wiley & Sons, Ltd.
Dysregulation of hedgehog signalling predisposes to synovial chondromatosis
Authors: Hopyan Sevan , Nadesan Puviindran , Yu Chunying , Wunder Jay , Alman Benjamin A 
Published: April 2005

AbstractSynovial chondromatosis is a condition affecting joints in which metaplastic cartilage nodules arise from the synovium, causing pain, joint dysfunction, and ultimately joint destruction. Because dysregulation of hedgehog signalling is a feature of several benign cartilaginous tumours, expression of the hedgehog target genes PTC1 and GLI1 was examined in this study in samples from human synovial chondromatosis. Significantly higher expression levels were found in synovial chondromatosis than in the synovium, from which it arises. To determine if hedgehog‐mediated transcription predisposes to synovial chondromatosis, the extra‐toes mutant mouse, which harbours a heterozygous mutation in the hedgehog transcriptional repressor, Gli3, resulting in decreased expression of Gli3 protein, was studied. The extra‐toes mutant mouse has a phenotype consistent with overactive hedgehog signalling, suggesting that Gli3 acts as a transcriptional repressor of limb development. Eighty‐five per cent of Gli3 mutant mice developed synovial chondromatosis at 18 months of age, compared with 30% of wild‐type littermates (p < 0.05). Three of the ten Gli3 mutant mice treated with triparanol, which blocks hedgehog signalling upstream of the Gli transcription factors, developed synovial chondromatosis, compared with eight of ten control mice. These data demonstrate that hedgehog signalling plays an important role in the development of synovial chondromatosis and suggest that blockade of hedgehog signalling may be a potential treatment for this disorder. Copyright © 2005 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
Preparation of chiral polystyrene monoliths by utilizing W/O emulsion polymerization and their optical resolution ability
Authors: Teraguchi Masahiro , Ohtake Miyako , Inoue Hiroshi , Yoshida Akiko , Aoki Toshiki , Kaneko Takashi , Yamanaka Koji 
Published: April 2005

AbstractWe synthesized two kinds of chiral polystyrene‐based monoliths, which are macroporous gel with continuous open‐celled monolith structure. Thus, two chiral styrene monomers, (–)‐p‐[dimethyl(10‐pinanyl)silyl]styrene ((–)‐PSSt) and (–)‐p‐(menthoxycarbonyl)styrene ((–)‐MtSt]), were prepared and subjected to water‐in‐oil emulsion polymerization in the presence of divinylbenzene and AIBN. The macroporous structure of the obtained monoliths was directly confirmed by SEM observation. The obtained monoliths showed an optical resolution ability. That is, in the enantioselective adsorption using trans‐stilbene oxide, poly[(–)‐PSSt] monolith and poly[(–)‐MtSt] monoliths preferentially adsorbed (S,S)‐isomer [poly[(–)‐PSSt] monolith: α(S,S) = 1.49 (0.25 wt % acetone solution); poly[(–)‐MtSt] monolith: α(S,S) = 1.39 (0.25 wt % toluene solution)]. Depinanylsilylation of the poly[(−)‐PSSt] monolith and removal of menthyl groups from the poly[(–)‐MtSt] monolith were achieved by acid‐catalyzed scission of the SiC bond and base‐catalyzed hydrolysis, respectively. In addition, de‐poly[(–)‐PSSt] and de‐poly[(–)‐MtSt] showed enantioselectivity ((S,S)‐isomer preferentially absorbed) in adsorption using trans‐stilbene oxide in spite of the absence of chiral substituents in the monoliths. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2348–2357, 2005
Novel catalyst compositions for the syndiospecific polymerization of styrene prepared by the combination of cyclopentadenyl complexes of group IIA or group IIIA elements with titanium alkoxides
Authors: Tsai Jing‐Cherng , Kuo Jing Chung , Chen Yi‐Chun 
Published: April 2005

AbstractA highly reactive catalyst system, which induces the syndiospecific polymerization of styrene with high activity, has been found by the combination of cyclopentadienyl (Cp) complexes of group IIA or group IIIA elements with titanium alkoxides. The 1H NMR monitoring of these reactions reveals the occurrence of a novel Cp‐transfer reaction that leads to the generation of Cp‐containing titanium complexes as catalysts for promoting the syndiospecific polymerization of styrene. Detailed in situ 1H NMR studies reveal that the rate of the Cp‐transfer reaction is highly dependent on the steric bulkiness of the titanium alkoxide complexes, the structures of the Cp complexes of group IIA or group IIIA elements, and the polymerization temperature. Styrene polymerization studies also reveal that a more effective Cp‐transfer reaction can typically lead to the generation of a more highly reactive catalyst for sPS polymerization. This study provides a convenient method for the in situ generation of variable structures of Cp/titanium alkoxide complexes, which are difficult to synthesize by other methods. Most importantly, the mixture of a catalyst precursor can be directly used as an sPS polymerization catalyst without isolation and purification of Cp/titanium complexes. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2304–2315, 2005
Some mechanisms for subtle influences of stereochemical composition on the physical properties of macromolecules
Authors: Mattice Wayne L. , Helfer Carin A. , Rane Sagar S. , Von Meerwall Ernst D. , Farmer Barry L. 
Published: April 2005

AbstractCoarse‐grained chains can be designed so that they successfully capture subtle effects arising from the local covalent structure of real chains. Constraining the conformations of the coarse‐grained chains with an appropriate rotational isomeric state model can achieve this objective. This claim has been documented by simulations of the dependence of the mixing behavior of polypropylene melts on the stereochemical composition of the chains; atactic polypropylene and isotactic polypropylene are miscible, but the replacement of either component with syndiotactic polypropylene can lead to immiscibility. This has also been documented by a comparison of simulations and infrared–visible sum frequency generation spectroscopy studies of the surface structures of atactic polystyrene and random copolymers of ethylene and propylene. The success of this method when the stereochemical composition is defined by side chains as small as CH3suggests that it should also be applicable to other problems in which the influence of the stereochemical composition is less subtle because the stereochemistry is defined by larger side chains. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1271‐1282, 2005
A laboratory‐based comparison of a molluscicide and an alternative food source (red clover) as means of reducing slug damage to winter wheat
Authors: Brooks Andrew S , Wilcox Andrew , Cook Richard T , Crook Mitchell J 
Published: April 2005

AbstractSlugs are major pests of many crops in the UK, including winter wheat, yet current methods of control are often unreliable. This study investigates the potential use of red clover, as an alternative food source, to reduce the amount of damage caused to winter wheat by the field slug, Deroceras reticulatum (Müller). Two laboratory‐based studies, each conducted over a 7‐day period, investigated the effects of red clover seedlings and commercial metaldehyde pellets on damage to winter wheat seeds and seedlings. The results indicate that metaldehyde applications, in the form of commercially available pellets, resulted in significantly greater protection to wheat seeds compared with red clover, whereas metaldehyde and red clover were equally as effective in reducing damage to wheat seedlings. A further laboratory experiment investigated the effect of two slug population densities (48 and 16 adults m−2) and high and low red clover seed rates (125% and 75% of a standard rate) on damage to wheat seeds. Results showed that, at the highest slug population density, red clover sown at 125% of the standard rate gave 99% protection to wheat seeds, compared with the 75% seed rate which gave 55%. At the lower slug population density, both seed rates of red clover resulted in similar levels of protection. Implications for the potential use of red clover as an alternative food source for reducing damage to winter wheat in field conditions are discussed. Copyright © 2005 Society of Chemical Industry
Application of a Photolabile Backbone Amide Linker for Cleavage of Internal Amides in the Synthesis towards Melanocortin Subtype‐4 Agonists
Authors: Minkwitz Rolf , Meldal Morten 
Published: April 2005

AbstractA new photolabile backbone amide handle has been developed for the synthesis of a melanocortin subtype‐4 receptor (MCR4) agonist library in the solid phase. This traceless linker allows for the solid‐supported synthesis of internal amides and their release under very mild, orthogonal conditions from solid support. The chemistry to attach an amide onto the linker is discussed. Structural variations of the linker in order to facilitate the attachment are investigated. The cleavage rate on the solid phase was measured. Finally, a small arylpiperazine library towards the MCR4 receptor was synthesized and its members characterized via HPLC, MS and NMR.
A novel coaxial electrospray ionization method for characterizing hexacosanoylceramides by Fourier transform ion cyclotron resonance mass spectrometry
Authors: Ramjit Harri G. , Newton Randall , Guare James P. 
Published: April 2005

AbstractBecause of poor aqueous solubility and lack of UV chromophores, the characterization of long‐chain hydrocarbons and ceramides by conventional UV and mass spectrometric methods has not been successful. Therefore, a novel coaxial electrospray ionization method was developed for characterizing reaction products of phytosphingosine and hexacosanoic acid in toluene and tetrahydrofuran (THF), by high resolving power Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS). Simultaneous spraying of a solution of apolar analytes and polar reagents into the gas phase readily enabled protonation and/or sodiation of analyte with enhanced signal‐to‐noise (S/N). Sample introduction was by direct infusion such that the sprayers were arranged either along the instrument line‐of‐sight (for monospray and coaxial spray modes) or in a 45° configuration for dual‐spray mode. For dual‐spray and coaxial spraying, p‐toluenesulphonic acid was used as a reagent and sprayed simultaneously with the analyte dissolved in toluene or THF. Compounds were characterized by accurate mass measurement of the protonated and/or sodiated molecules. Copyright © 2005 John Wiley & Sons, Ltd.
Synthesis and Crystal Structure of KLa[C(CN)3]4·H2O containing a Shielded Potassium Ion
Authors: Srinivasan Radhakrishnan , Tragl Sonja , Meyer H.‐Jürgen 
Published: April 2005

AbstractKLa[C(CN)3]4·H2O was crystallized from an aqueous solution containing La(NO3)3·6H2O and K[C(CN)3]. The crystal structure was solved and refined from X‐ray single crystal data (P4/n, Z = 2, a = b = 12.379(1) Å, c = 6.5695(8) Å, V = 1006.7(2) Å3). Solid KLa[C(CN)3]4·H2O forms a framework structure with bridging tricyanomethanide ions, each of them connecting two La3+ ions and one K+ ion. Potassium is apparently situated in a tetrahedral environment with four K–N distances of 2.741(3) Å, shielded by four other tricyanomethanide ions. Each La3+ has a square antiprismatic coordination of nitrogen atoms from eight [C(CN)3]– ions, and this antiprism is mono‐capped by one water molecule.
The Unsubstituted Rare Earth Pyrazolates [Nd(Pz)3(PzH)4] and [Ho(Pz)3(PzH)3]: Structural Diversity from Monomers to a Coordination Polymer
Authors: Quitmann Catharina C. , Müller‐Buschbaum Klaus 
Published: April 2005

AbstractThe high‐temperature oxidation of the rare earth metals holmium and neodymium with the amine pyrazole gave the two new compounds [Ho(Pz)3(PzH)3] (1) and [Nd(Pz)3(PzH)4] (2) (pyrazole, PzH = C3H3NNH; pyrazolate anion, Pz− = C3H3NN−). 1 exhibits a one dimensional chain structure with the unusually high number of twelve nitrogen atoms that form a hexagonal antiprism as coordination polyhedra around HoIII. 2 consists of monomeric molecules containing trivalent neodymium with the coordination number of nine. The coordination polymer 1 shows both a higher thermal stability as well as a packing of a dinstinctively higher density than monomeric 2. Both compounds were investigated by low‐temperature single crystal X‐ray analysis, Mid IR, Far IR and Raman spectroscopy. Simultaneous DTA/TG and temperature dependent x‐ray powder diffraction were used as combinatory methods to investigate the thermal properties of both compounds.
A Molecular Dynamics Simulation Study of (OH−) Schottky Defects in Hydroxyapatite
Authors: Zahn Dirk , Hochrein Oliver 
Published: April 2005

AbstractThe dynamics of (OH−) Schottky defects is investigated for a hydroxyapatite / vacuum interface and in the bulk crystal. From our molecular dynamics simulations the mechanism of such defect translocation is identified. The hydroxide ions are arranged in [001] channels formed by staggered triangles of calcium ions. Above 200 °C, the OH− ions start to invert their orientation by passing through the surrounding Ca2+ triangle. In the neighborhood of an empty calcium triangle, the OH− orientation inversion may also occur by hydroxide ion translocation from the occupied to the unoccupied calcium triangle. The later process causes the hydroxide to jump by c/2 ≈ ±3.5Å along the [001] direction. From an Arrhenius plot the activation energy of (OH−) Schottky defect diffusion in the bulk crystal was found as 73 kJ mol−1. At the hydroxyapatite/vacuum interface, OH− defect sintering exhibited a preference of Schottky defects diffusion to the surface.
Prediction of Possible High‐Pressure Phases of Cu3N
Authors: Cancarevic Z. , Schön J. C. , Jansen M. 
Published: April 2005

AbstractThe possibility of Cu3N in the form of high‐pressure phases has been investigated by theoretical methods. Structure candidates that had been found during the investigation of the enthalphy landscapes of various nitridic M3N‐type compounds have been locally optimized within the Hartree‐Fock and DFT‐approximation. It is found that at high pressures several phases might be stable, with the most likely transition to occur from the experimentally observed low‐pressure phase (ReO3‐type) to the Li3P‐type, the α‐UO3‐type or the I‐K3N‐type at about 25–35 GPa.
Zur Synthese von binären und ternären Carbiden in einem modifizierten Haushaltsmikrowellenofen
Authors: Ahlers Ruth , Ruschewitz Uwe 
Published: April 2005

AbstractOn the Synthesis of Binary and Ternary Carbides in a Modified Domestic Microwave OvenBy modifying a domestic microwave oven binary and ternary carbides were synthesized from the elements in an argon atmosphere. We succeded in preparing CaC2, Ca4Ni3C5 and MgM3Cx (M = Ni, Co) within several minutes. Well crystallized product powders were obtainend with purities as high as 90 % (CaC2, MgNi3Cx). In the case of MgNi3Cx our experiments show that a product with a high carbon content (x ≈ 1) is only synthesized under optimized conditions (magnesium surplus, reaction time). This product exhibits the expected superconductivity with a critical temperature of approx. 6 K. The syntheses and possible structures of MgPdCxHy (x = 0.4‐0.8, y = 0.4‐2.3) and MgPtC0,06H0,32 are briefly discussed.