bluuebunny/crossref_metadata_2025 huggingface dataset:
High‐resolution NMR spectroscopic trends and assignment rules of metal‐free, metallated and substituted corroles
Authors: Balazs Yael S. , Saltsman Irena , Mahammed Atif , Tkachenko Elena , Golubkov Galina , Levine Joshua , Gross Zeev
Published: June 2004

Major advances over the last few years have facilitated the synthesis of a large variety of meso‐only substituted corroles that display interesting catalytic, therapeutic and photophysical properties. This work is the first to study extensively the NMR spectral characteristics of both metallated and non‐metallated triarylcorroles in various organic solvents and provide guidelines for easy and reliable assignments of 1D 1H spectra from trends of J coupling constants and chemical shifts. An excellent correlation is found between CC bond lengths derived from 3J(H,H) values and experimental lengths determined by x‐ray crystallography of the same molecules. The nuclear Overhauser effect provides a robust 1D 1H NMR tool for determining the selectivity of electrophilic substitutions. Variable‐temperature NMR and isotopic labelling reveal a single preferred tautomerization state and unsymmetric ring orientations at −70°C. The β‐pyrrole protons demonstrate long‐range heteronuclear couplings with the coordination core (15N) and with the ortho‐19F nuclei of the meso‐carbon aryl rings. In sum, application of multinuclear magnetic resonance to corroles and their metal complexes, through the compilation of chemical shifts and J couplings and the recognition of trends therein, provides basic information essential to reliable spectral assignments. Additionally, the conclusions drawn about the structures of corroles and the electron densities at various positions of the corrole macrocycle resulting from the application of high‐resolution NMR techniques are of importance to an in‐depth understanding of the molecular interactions and processes of this relatively new and rapidly expanding class of compounds. Copyright © 2004 John Wiley & Sons, Ltd.
Heteronuclear selective refocusing 2D NMR experiments for the spectral analysis of enantiomers in chiral oriented solvents
Authors: Farjon Jonathan , Baltaze Jean‐Pierre , Lesot Philippe , Merlet Denis , Courtieu Jacques
Published: June 2004

We report the use of carbon–proton heteronuclear selective refocusing 2D NMR experiments dedicated to the spectral analysis of enantiomers dissolved in weakly ordering chiral liquid crystalline solvents. The method permits the extraction of carbon–proton residual dipolar couplings for each enantiomer from a complex or unresolved proton‐coupled 13C spectral patterns. Illustrative examples are analysed and discussed. It is shown that an accurate determination of enantiomeric excess is possible. Copyright © 2004 John Wiley & Sons, Ltd.
Collagen synthesis is not altered in women with stress urinary incontinence
Authors: Chen Yu , DeSautel Michael , Anderson Ann , Badlani Gopal , Kushner Leslie
Published: June 2004

Aims

The objective of this study was to demonstrate that weakened pelvic floor support of the lower genitourinary tract in women with stress urinary incontinence (SUI) is due, in part, to decreased collagen synthesis and secretion and/or an altered ratio of collagen III/I synthesis by the fibroblasts of the endopelvic fascia and skin compared to that of women without evidence of pelvic floor weakening.

Methods

Endopelvic fascia and skin biopsies were obtained from women with SUI (n = 14) and women without evidence of SUI or genital prolapse (n = 12). Fibroblast cultures established from the biopsies were incubated with 3H‐proline in medium containing ascorbic acid for 3 hr. Conditioned medium was collected and cells were harvested. The radiolabeled collagens were precipitated and digested with collagenase. The collagen synthesized (as a percent of total protein) was determined. Collagen α1(III) was separated from collagen α1(I) and α2(I) by interrupted SDS‐PAGE and the amount of 3H‐proline in each band was determined.

Results

Collagen synthesis, expressed as percent of total protein synthesis, was not significantly different between fibroblasts obtained from women with or without SUI. The mean of collagen III/I synthesized in fibroblasts was not significantly different between fibroblasts obtained from women with or without SUI.

Conclusions

These data suggest that the lower collagen content in the endopelvic fascia and skin of women with SUI is not due to reduced collagen synthesis or selective reduction in synthesis of either collagen I or collagen III, compared to women without pelvic floor weakening. © 2004 Wiley‐Liss, Inc.
Pelvic floor maximal strength using vaginal digital assessment compared to dynamometric measurements
Authors: Morin M. , Dumoulin C. , Bourbonnais D. , Gravel D. , Lemieux M.‐C.
Published: June 2004

Aim

To compare vaginal digital assessment with dynamometric measurements for determining the maximal strength of the pelvic floor muscles (PFM).

Materials and Methods

Eighty‐nine women aged between 21 and 44 participated in the study. An experienced physiotherapist evaluated the maximal strength of the PFM of these women using the modified Oxford grading system (six categories, range 0–5) and dynamometric measurements. The mean maximal forces obtained for all women with the instrumented speculum for each category of digital assessment were compared using ANOVAs. Spearman's rho coefficients were calculated to assess the correlation between the dynamometric and the digital assessments.

Results

According to their symptoms and pad test results, 30 women were continent and 59 had stress urinary incontinence (SUI). Based on dynamometric measurements, important overlaps were observed between each category of digital assessment. The ANOVAs indicated that force values differ across categories (F = 10.08; P < 0.001), although contrast analyses revealed no differences in the mean maximal forces between adjacent digital‐assessment categories (1–2, 2–3, 3–4, 4–5). Mean force values differed significantly only between non‐adjacent levels in digital assessment, for example, between 1 and 3; 1 and 4; 1 and 5; 2 and 4; 2 and 5 (P < 0.05). Significant correlations were found between the two measurements with coefficients of r = 0.727, r = 0.450, and r = 0.564 for continent, incontinent, and all women, respectively (P < 0.01).

Conclusions

Even if the dynamometric mean forces of the PFM increased across subsequent categories of digital assessment, the force values between two adjacent categories do not differ. This limitation of digital assessment should be considered by clinicians and researchers when choosing treatment orientation and evaluating treatment outcomes. © 2004 Wiley‐Liss, Inc.
Mast cell chymase is a possible mediator of neurogenic bladder fibrosis
Authors: Howard Pamela S. , Renfrow David , Schechter Norman M. , Kucich Umberto
Published: June 2004

Aims

Urinary bladders of patients with myelomeningocele, owing to spina bifida, are often functionally impaired, fibrotic organs. Common to this condition are repeated occurrences of bladder infection and inflammation. Since mast cells have been associated with a fibrogenic response in inflammatory conditions, we investigated the role of mast cell granule product, chymase, as a mediator of myleodysplastic bladder fibrosis.

Methods

Human control and myelodysplastic bladder tissues were stained with Unna's stain and chymase antibody to determine mast cell number and localization. Cell specific localization of collagen mRNAs was determined by in situ hybridization (ISH). In vitro, normal human bladder fibroblasts were treated with recombinant chymase, heparin and inhibitors, and collagen subtype concentration was determined by enzyme linked immunosorbent assay (ELISA).

Results

Myelodysplastic bladders were characterized by increased mast cells in the detrusor muscle layer compared to control bladders, as well as mast cell degranulation and increased connective tissue deposition. Both types I and III collagen mRNA localized to fibroblasts surrounding detrusor muscle fascicles, whereas only collagen III mRNA localized to cells within connective tissue infiltrated muscle bundles in myelomeningocele bladder tissue. Chymase treatment of bladder fibroblasts, in vitro, was dose‐dependent and resulted in significant increases in both types I and III collagen. Heparin did not alter collagen protein expression, whereas heparin–chymase combination modulated type III collagen expression. Serine protease inhibitor, phenylmethylsulfonlyfluoride, did not inhibit collagen synthesis, whereas denatured chymase resulted in decreased collagenous protein levels.

Conclusions

Bladder fibrosis may be mediated by mast cell chymase stimulation of collagen synthesis. © 2004 Wiley‐Liss, Inc.
Oral Kohki Tea and its protective effect against in vitro ischemic damage to the bladder
Authors: Levin Robert M. , Leggett Robert E. , Whitbeck Catherine , Murakami Toshiyuki , Kambara Toshimitsu , Aikawa Ken
Published: June 2004

Aims

Results of several studies indicate that ischemia/reperfusion (I/R) is an etiological factor in the contractile dysfunctions induced by partial bladder outlet obstruction in animal models. In support of this hypothesis, pretreatment of rabbits with Kohki Tea (Engelhardtia chrysolepis), a Japanese herbal drink very high in antioxidant activity, significantly reduced the contractile dysfunctions induced by partial outlet obstruction. The current study was designed to determine if pretreating rabbits with Kohki Tea could protect the bladder against the contractile damage induced by in vitro ischemia followed by re‐oxygenation.

Methods

Forty‐eight New Zealand White rabbits were separated into two groups of 24; Group 1 was pretreated by oral gavage for 3 weeks with Kohki Tea and Group 2 received vehicle (water). Each rabbit was anesthetized with pentobarbital. The urinary bladder was rapidly removed and eight longitudinal muscle strips were cut from the bladder body. Each strip was mounted in a separate 15‐ml bath containing Tyrode's solution with glucose (1 mg/ml) and maintained at 37°C. All strips were equilibrated for 30 min with a gas mixture of 95% O2 and 5% CO2. At the end of this period of time, all strips were stimulated with field stimulation (FS) carbachol and KCl. After the last wash, the aeration was changed to hypoxic mixture (nitrogen–CO2) without glucose. At the end of 2 hr, the aeration was changed back to the normal 95% O2 and 5% CO2, and glucose was added to the buffer. After 1 hr of re‐oxygenation, a second set of stimulations was performed. In order to represent hyperreflexia, the strips were stimulated at 32‐Hz FS at 5‐min intervals during the hypoxic period in half of the in vitro experiments.

Results

The results showed that Kohki Tea pretreatment protected the bladder's response to FS from the detrimental effects of repetitive stimulation and the detrimental effects of both in vitro ischemia and repetitive stimulation on the contractile responses to carbachol and KCl.

Conclusions

These data are consistent with the concept that Kohki Tea acts by protecting the bladder from cellular damage caused by hypoxia and the generation of free radicals. © 2004 Wiley‐Liss, Inc.
Changes in intracellular calcium concentration and P2X1 receptor expression in hypertrophic rat urinary bladder smooth muscle
Authors: Scott R. Sjuve , Uvelius B. , Arner A.
Published: June 2004

Aims

Contractile responses to purinergic activation in the urinary bladder are altered in outflow obstruction (O). We determined if the lowered contractile response to adenosine triphosphate (ATP) in obstructed rat urinary bladder was due to changes in calcium handling or in P2X1 purinoceptor density.

Materials and Methods

O was created in rat by partial ligature of the urethra, with non‐obstructed rats as controls (C). Force and intracellular calcium were measured in bladder strips activated with ATP. Tissue was sectioned for light and electron microscopy and analyzed with Western blot using a P2X1 antibody.

Results

Bladder weight increased from 66 ± 3 (C) to 206 ± 17 mg (O) (n = 6). ATP gave a transient contractile response which was decreased in the obstructed strips (C: 161 ± 20; O: 63 ± 16% of high‐K+ force). Intracellular calcium concentration after ATP activation in the obstructed bladder muscle was about 50% of that in the control preparations (C: 669 ± 110; O: 335 ± 59 nM). Half‐time for calcium influx was increased in the O group. P2X1 immunoreactivity per unit bladder weight was similar in the two groups. Cell membrane area per unit wet weight was decreased in the O group.

Conclusions

Attenuated contractile responses to ATP in obstructed rat urinary bladder are due to a lowered rate of calcium influx and maximal peak calcium concentration. This change in Ca2+ transients is not due to a decrease in P2X1 receptor density in the smooth muscle cell membranes. Possibly, the increase in cell volume buffers the rapid and transient influx of Ca2+ following purinoceptor activation in the obstructed bladder. © 2004 Wiley‐Liss, Inc.
Basic science and translational research in female pelvic floor disorders: Proceedings of an NIH‐sponsored meeting
Authors: Weber Anne M. , Buchsbaum Gunhilde M. , Chen Bertha , Clark Amanda L. , Damaser Margot S. , Daneshgari Firouz , Davis Gary , DeLancey John , Kenton Kimberly , Weidner Alison C. , Word R. Ann
Published: June 2004

Aims

To report the findings of a multidisciplinary group of scientists focusing on issues in basic science and translational research related to female pelvic floor disorders, and to produce recommendations for a research agenda for investigators studying female pelvic floor disorders.

Methods

A National Institutes of Health (NIH)‐sponsored meeting was held on November 14–15, 2002, bringing together scientists in diverse fields including obstetrics, gynecology, urogynecology, urology, gastroenterology, biomechanical engineering, neuroscience, endocrinology, and molecular biology. Recent and ongoing studies were presented and discussed, key gaps in knowledge were identified, and recommendations were made for research that would have the highest impact in making advances in the field of female pelvic floor disorders.

Results

The meeting included presentations and discussion on the use of animal models to better understand physiology and pathophysiology; neuromuscular injury (such as at childbirth) as a possible pathogenetic factor and mechanisms for recovery of function after injury; the use of biomechanical concepts and imaging to better understand the relationship between structure and function; and molecular and biochemical mechanisms that may underlie the development of female pelvic floor disorders.

Conclusions

While the findings of current research will help elucidate the pathophysiologic pathways leading to the development of female pelvic floor disorders, much more research is needed for full understanding that will result in better care for patients through specific rather than empiric therapy, and lead to the potential for prevention on primary and secondary levels. © 2004 Wiley‐Liss, Inc.
Constitutive expression of p21H‐rasVal12 in pyramidal neurons results in reorganization of mouse neocortical afferents
Authors: Alpár Alán , Gärtner Ulrich , Seeger Gudrun , Härtig Wolfgang , Brauer Kurt , Arendt Thomas
Published: June 2004

The effect of constitutive expression of p21H‐rasVal12 in pyramidal neurons upon the establishment of afferent input has been investigated in the primary somatosensory cortex of transgenic mice. In these animals, relevant transgene expression is confined to cortical pyramidal neurons and starts postnatally at a period when neuronal morphogenesis has been largely completed. We have shown recently that overexpression of p21H‐rasVal12 in these cells results in considerable enlargement of their size and consequently in expansion of the cortex. In the present study we demonstrate that the density of terminals representing intra‐ or interhemispheric afferents within cortical layers II/III, however, is only slightly decreased. The density of thalamocortical boutons within layer IV is even higher and the number of afferent contacts to transgenic pyramidal neurons is significantly increased compared to the wild‐type. The number of catecholaminergic and cholinergic terminals is augmented proportionally to cortical size or even overproportionally, respectively. Along intercortical and striatal fibers arising from p21H‐rasVal12‐expressing pyramidal neurons, frequency of varicosities is significantly increased, but remains unchanged on cortical cholinergic and catecholaminergic axons originating from “nontransgenic” neurons. Additionally, a higher number of multiple synaptic bodies are found in transgenic mice, suggesting subtle effects on synaptic plasticity. It is concluded that the enlargement of pyramidal neurons due to transgenic expression of p21H‐rasVal12 is paralleled by significant changes in the quantity and pattern of afferent connections. Moreover, expression of p21H‐rasVal12 in pyramidal cells induces an enhanced establishment of efferent boutons. © 2004 Wiley Periodicals, Inc. J Neurobiol 60: 263–274, 2004
Repetitive exposures to nicotine induce a hyper‐responsiveness via the cAMP/PKA/CREB signal pathway in Drosophila
Authors: Hou Jiamei , Kuromi Hiroshi , Fukasawa Yohko , Ueno Kohei , Sakai Takaomi , Kidokoro Yoshiaki
Published: June 2004

Nicotine, in addition to acute effects, has long‐lasting effects on mammalian behaviors, such as those leading to addiction. Here we present genetic and pharmacological evidence in Drosophila suggesting that repetitive exposures to nicotine induce a hyper‐responsiveness through synthesis of new protein(s) via CREB‐mediated gene transcription. Single exposure to volatilized nicotine dose‐dependently inhibited the startle‐induced climbing response. Compared with this effect of nicotine in wild‐type flies, it was stronger in dunce, which has defective phosphodiesterase, and in wild‐type flies treated with a phosphodiesterase inhibitor, whereas it was weaker in DC0, which has defective protein kinase A (PKA), and in wild‐type flies treated with a PKA blocker. Thus, the effect of nicotine is enhanced by a mechanism involving the cAMP/PKA cascade. However, in wild‐type flies, an increase in head cAMP was not detected within 2 min after single exposure to nicotine, during which the nicotine effect on the behavior was maximal. In wild‐type flies, after repetitive exposures to nicotine, the nicotine effect was significantly enhanced and the head cAMP was elevated. The responsiveness to nicotine at second exposure increased with a 4 h interval but not with a 2 h interval, suggesting that the observed hyper‐responsiveness was not due to accumulation of residual nicotine. Both enhancement of the nicotine effect and elevation of cAMP during repetitive exposures to nicotine were blocked by a protein synthesis inhibitor. Induction of a dominant negative CREB transgene also blocked the enhancement, suggesting that CREB‐mediated gene transcription is required for the hyper‐responsiveness. © 2004 Wiley Periodicals, Inc. J Neurobiol 60: 249–261, 2004
Hedgehog and Fgf signaling pathways regulate the development of tphR‐expressing serotonergic raphe neurons in zebrafish embryos
Authors: Teraoka H. , Russell C. , Regan J. , Chandrasekhar A. , Concha M. L. , Yokoyama R. , Higashi K. , Take‐uchi M. , Dong W. , Hiraga T. , Holder N. , Wilson S. W.
Published: June 2004

Serotonin (5HT) plays major roles in the physiological regulation of many behavioral processes, including sleep, feeding, and mood, but the genetic mechanisms by which serotonergic neurons arise during development are poorly understood. In the present study, we have investigated the development of serotonergic neurons in the zebrafish. Neurons exhibiting 5HT‐immunoreactivity (5HT‐IR) are detected from 45 h postfertilization (hpf) in the ventral hindbrain raphe, the hypothalamus, pineal organ, and pretectal area. Tryptophan hydroxylases encode rate‐limiting enzymes that function in the synthesis of 5HT. As part of this study, we cloned and analyzed a novel zebrafish tph gene named tphR. Unlike two other zebrafish tph genes (tphD1 and tphD2), tphR is expressed in serotonergic raphe neurons, similar to tph genes in mammalian species. tphR is also expressed in the pineal organ where it is likely to be involved in the pathway leading to synthesis of melatonin. To better understand the signaling pathways involved in the induction of the serotonergic phenotype, we analyzed tphR expression and 5HT‐IR in embryos in which either Hh or Fgf signals are abrogated. Hindbrain 5HT neurons are severely reduced in mutants lacking activity of either Ace/Fgf8 or the transcription factor Noi/Pax2.1, which regulates expression of ace/fgf8, and probably other genes encoding signaling proteins. Similarly, serotonergic raphe neurons are absent in embryos lacking Hh activity confirming a conserved role for Hh signals in the induction of these cells. Conversely, over‐activation of the Hh pathway increases the number of serotonergic neurons. As in mammals, our results are consistent with the transcription factors Nk2.2 and Gata3 acting downstream of Hh activity in the development of serotonergic raphe neurons. Our results show that the pathways involved in induction of hindbrain serotonergic neurons are likely to be conserved in all vertebrates and help establish the zebrafish as a model system to study this important neuronal class. © 2004 Wiley Periodicals, Inc. J Neurobiol 60: 275–288, 2004
Chronic stress alters dendritic morphology in rat medial prefrontal cortex
Authors: Cook Susan C. , Wellman Cara L.
Published: June 2004

Chronic stress produces deficits in cognition accompanied by alterations in neural chemistry and morphology. Medial prefrontal cortex is a target for glucocorticoids involved in the stress response. We have previously demonstrated that 3 weeks of daily corticosterone injections result in dendritic reorganization in pyramidal neurons in layer II–III of medial prefrontal cortex. To determine if similar morphological changes occur in response to chronic stress, we assessed the effects of daily restraint stress on dendritic morphology in medial prefrontal cortex. Male rats were exposed to either 3 h of restraint stress daily for 3 weeks or left unhandled except for weighing during this period. On the last day of restraint, animals were overdosed and brains were stained using a Golgi‐Cox procedure. Pyramidal neurons in lamina II–III of medial prefrontal cortex were drawn in three dimensions, and the morphology of apical and basilar arbors was quantified. Sholl analyses demonstrated a significant alteration of apical dendrites in stressed animals: overall, the number and length of apical dendritic branches was reduced by 18 and 32%, respectively. The reduction in apical dendritic arbor was restricted to distal and higher‐order branches, and may reflect atrophy of terminal branches: terminal branch number and length were reduced by 19 and 35%. On the other hand, basilar dendrites were not affected. This pattern of dendritic reorganization is similar to that seen after daily corticosterone injections. This reorganization likely reflects functional changes in prefrontal cortex and may contribute to stress‐induced changes in cognition. © 2004 Wiley Periodicals, Inc. J Neurobiol 60: 236–248, 2004
RhoA/ROCK and Cdc42 regulate cell‐cell contact and N‐cadherin protein level during neurodetermination of P19 embryonal stem cells
Authors: Laplante Isabel , Béliveau Richard , Paquin Joanne
Published: June 2004

RhoGTPases regulate actin‐based signaling cascades and cellular contacts. In neurogenesis, their action modulates cell migration, neuritogenesis, and synaptogenesis. Murine P19 embryonal stem cells differentiate to neurons upon aggregation in the presence of retinoic acid, and we previously showed that RhoA and Cdc42 RhoGTPases are sequentially up‐regulated during neuroinduction, suggesting a role at this very early developmental stage. In this work, incubation of differentiating P19 cells with C3 toxin resulted in decreased aggregate cohesion and cadherin protein level. In contrast, C3 effects were not observed in cells overexpressing recombinant dominant active RhoA. On the other hand, C3 did not affect cadherin in uninduced cells and their postmitotic neuronal derivatives, respectively expressing E‐ and N‐cadherin. RhoA is thus influential on cell aggregation and cadherin expression during a sensitive time window that corresponds to the switch of E‐ to N‐cadherin. Cell treatment with Y27632 inhibitor of Rho‐associated‐kinase ROCK, or advanced overexpression of Cdc42 by gene transfer of a constitutively active form of the protein reproduced C3 effects. RhoA‐antisense RNA also reduced cadherin level and the size of cell aggregates, and increased the generation of fibroblast‐like cells relative to neurons following neuroinduction. Colchicin, a microtubule disrupter, but not cytochalasin B actin poison, importantly decreased cadherin in neurodifferentiating cells. Overall, our results indicate that the RhoA/ROCK pathway regulates cadherin protein level and cell‐cell interactions during neurodetermination, with an impact on the efficiency of the process. The effect on cadherin seems to involve microtubules. The importance of correct timing of RhoA and Cdc42 functional expression in neurogenesis is also raised. © 2004 Wiley Periodicals, Inc. J Neurobiol 60: 289–307, 2004
Updated Lagrangian free surface flow simulations with natural neighbour Galerkin methods
Authors: Martínez M. A. , Cueto E. , Alfaro I. , Doblaré M. , Chinesta F.
Published: June 2004

In this paper, a new method to simulate free surface fluid flows within an updated Lagrangian framework is described. It is based on the use of a meshless technique coined as natural element method (NEM) or, more recently, as natural neighbour Galerkin method. The position of the flow front or the geometry of the fluid domain is handled by invoking the geometrical concept of α‐shape of the cloud of points, thus avoiding the explicit definition of the boundary of the domain as it evolves. This method also avoids the traditional need of remeshing typical in finite element simulations of this kind of processes. Three types of fluid behaviour have been considered, namely a purely Newtonian fluid, a non‐Newtonian short fibre‐reinforced thermoplastic, and finally a Norton–Hoff viscoplastic behaviour. Benchmark examples showing the performance of the technique are included in the paper. Copyright © 2004 John Wiley & Sons, Ltd.
Three‐dimensional finite element computations for frictional contact problems with non‐associated sliding rule
Authors: Hjiaj M. , Feng Z‐Q , de Saxcé G. , Mróz Z.
Published: June 2004

This paper presents an algorithm for solving anisotropic frictional contact problems where the sliding rule is non‐associated.The algorithm is based on a variational formulation of the complex interface model that combine the classical unilateral contact law and an anisotropic friction model with a non‐associated slip rule. Both the friction condition and the sliding potential are elliptical and have the same principal axes but with different semi‐axes ratio. The frictional contact law and its inverse are derived from a single non‐differentiable scalar‐valued function, called a bi‐potential. The convexity properties of the bi‐potential permit to associate stationary principles with initial/boundary value problems. With the present formulation, the time‐integration of the frictional contact law takes the form of a projection onto a convex set and only one predictor–corrector step addresses all cases (sticking, sliding, no‐contact). A solution algorithm is presented and tested on a simple example that shows the strong influence of the slip rule on the frictional behaviour. Copyright 2004 John Wiley & Sons, Ltd.
Numerical integration in Natural Neighbour Galerkin methods
Authors: González D. , Cueto E. , Martínez M. A. , Doblaré M.
Published: June 2004

In this paper, issues regarding numerical integration of the discrete system of equations arising from natural neighbour (natural element) Galerkin methods are addressed. The sources of error in the traditional Delaunay triangle‐based numerical integration are investigated. Two alternative numerical integration schemes are analysed. First, a ‘local’ approach in which nodal shape function supports are exactly decomposed into triangles and circle segments is shown not to give accurate enough results. Second, a stabilized nodal quadrature scheme is shown to render high levels of accuracy, while resulting specially appropriate in a Natural Neighbour Galerkin approximation method. The paper is completed with several examples showing the performance of the proposed techniques. Copyright © 2004 John Wiley & Sons, Ltd.
Rayleigh wave correction for the BEM analysis of two‐dimensional elastodynamic problems in a half‐space
Authors: Arias I. , Achenbach J. D.
Published: June 2004

A simple, elegant approach is proposed to correct the error introduced by the truncation of the infinite boundary in the BEM modelling of two‐dimensional wave propagation problems in elastic half‐spaces. The proposed method exploits the knowledge of the far‐field asymptotic behaviour of the solution to adequately correct the BEM displacement system matrix for the truncated problem to account for the contribution of the omitted part of the boundary. The reciprocal theorem of elastodynamics is used for a convenient computation of this contribution involving the same boundary integrals that form the original BEM system. The method is formulated for a two‐dimensional homogeneous, isotropic, linearly elastic half‐space and its implementation in a frequency domain boundary element scheme is discussed in some detail. The formulation is then validated for a free Rayleigh pulse travelling on a half‐space and successfully tested for a benchmark problem with a known approximation to the analytical solution. Copyright © 2004 John Wiley & Sons, Ltd.
Fiber orientation structures and mechanical properties of injection molded short glass fiber reinforced ribbed plates
Authors: Hine P. J. , Duckett R. A.
Published: June 2004

In this paper we describe a study of the fiber orientation structures present within a model ribbed injection molded plate. The details of the fiber orientation at each chosen location on the injection molded parts were measured using an in‐house developed image analysis system, which enabled large areas to be scanned (up to 200 mm2) up to a limit of 1 million fiber images. Two materials were used for these experiments, short glass fiber filled PBT and short glass fiber filled nylon 66. First, a comparison was made between the fiber orientation at an identical position, 28 mm from the injection gate on a transverse rib, on two plates made from glass fiber filled PBT. It was found that the fiber orientation in these two separately manufactured components was virtually identical when comparing the whole scanned area, but the differences became more significant when comparing areas on the length scale of an individual fiber (∼ 200 μm). Second, the fiber orientation at the same position was compared for two plates made using the glass/PBT and glass/nylon 66 materials. The differences for the complete scanned areas were small, confirming that mold geometry plays a crucial role in determining fiber orientation structures, and that matrix properties are secondary. Third, the fiber orientation structures at various positions across one of the glass/PBT plates were examined in greater detail, in particular across a number of the transverse ribs: the chosen ribs were of various widths and heights. Differences in structure were found depending on the local rib geometry. Finally, the effect of the measured fiber orientation structures in determining the mechanical properties of the ribbed plate was investigated using simple modeling schemes. While the stiffness of the rib/web assembly was found to depend on the average fiber orientation of the two parts, the different thermal expansions of the web and the rib, caused by the different fiber orientation in the two regions, led to significant warpage of the rib/web assembly. Polym. Compos. 25:237–254, 2004. © 2004 Society of Plastics Engineers.
A new kinetic and viscosity model for liquid composite molding simulations in an industrial environment
Authors: Henne Markus , Breyer Christian , Niedermeier Michael , Ermanni Paolo
Published: June 2004

Liquid composite molding is broadly used for manufacturing composite parts. Apart from the preforming of the dry fibrous material, mold filling and curing of the resin are the main steps in the manufacturing process. For process simulation numerical methods, like finite element methods are applied. Flow models describing the flow behavior through a porous medium are well established. The ability to predict and monitor the curing process in liquid composite molding is crucial for manufacturing process optimization in case of application of rapid curing resin systems. Based on differential scanning calorimetry and rheological experiments, cure kinetics and viscosity of a resin system were characterized. A new kinetic and complex viscosity model is proposed to predict epoxy resin properties in numerical modeling of liquid composite molding. The semi‐empirical models are simple to use and therefore suitable for process optimization in an industrial environment. Both models were validated by a fitting to the experimental data by the Levenberg‐Marquardt method. A process to determine the initial values for the fitting procedure is also proposed. The predictions of the validated models were in good agreement with the measured data, and are therefore applicable for numerical process optimization. Polym. Compos. 25:255–269, 2004. © 2004 Society of Plastics Engineers.
Thermally induced performance decay in conductive polymer composites
Authors: Hou Yan Hui , Zhang Ming Qiu , Rong Min Zhi
Published: June 2004

In the course of long‐term service, electrically conductive polymer composites acting as positive temperature coefficient (PTC) materials are faced with performance decay characterized by gradually increased room temperature resistivity and decreased PTC intensity. To reveal the influencing factors and to find appropriate ways for solving the problems, thermal‐cold cycling experiments (which simulate the extreme operating conditions of PTC type materials in a laboratory environment) and electrification tests are carried out in the current work. The results demonstrate that irreversible damage of partial conductive networks and, in particular, oxidation degradation induced crystallizability deterioration of the matrix polymer are responsible for the electrical performance decay. Additionally, an increase in the contact resistance formed at the metallic electrode/composite contacts exerts a negative influence on the service life of the composites. Polym. Compos. 25:270–279, 2004. © 2004 Society of Plastics Engineers.
Creep behavior of biocomposites based on sisal fiber reinforced cellulose derivatives/starch blends
Authors: Alvarez Vera A. , Kenny José M. , Vázquez Analía
Published: June 2004

Biodegradable composites based on cellulose derivatives/starch blends reinforced with sisal short fibers were fabricated by injection molding. Results of short‐term flexural creep tests are reported to investigate the time‐dependence behavior of the composites. Fiber content and temperature effects are also considered, taking into account various methods and equations. At short times, a creep power law is employed. A master curve with the Arrhenius model is used to determine the creep resistance at longer times and different temperatures. Good fitting of the experimental results with the four‐parameter model is reported, leading to a relationship between the observed creep behavior and the composite morphology. The addition of sisal fibers to the polymeric matrix promotes a significant improvement of the composite creep resistance. Polym. Compos. 25:280–288, 2004. © 2004 Society of Plastics Engineers.
Long‐term behavior of partially cured epoxy prepreg systems under tensile loading
Authors: Wolfrum J. , Stang C. , Ehrenstein G. W.
Published: June 2004

For the determination of the influence of processing conditions on the long‐term behavior of high performance thermoset composites, two different glass fiber laminate systems with varying degrees of cure were examined. The laminates were conditioned in both moist and dry environments, and characterized via thermoanalytical and mechanical investigations. During the progression of moisture conditioning, both systems exhibited a reduction in the measured glass transition temperature as a result of the plasticization of the matrix. Tensile tests revealed that a direct correlation exists between the processing conditions and the long‐term performance. Employing a linear model, the long‐term mechanical behavior as a function of processing and moisture absorption can be described. Thus, the manufacturer has access to a tool for calculating the mechanical and thermomechanical properties depending on the processing and environmental conditions. Polym. Compos. 25:289–297, 2004. © 2004 Society of Plastics Engineers.
Fast joining of composite pipes using UV curing FRP composites
Authors: Pang Su‐Seng , Li Guoqiang , Jerro H. Dwayne , Peck Jerry A. , Stubblefield Michael A.
Published: June 2004

In this paper, twelve butt‐weld composite pipe joints were prepared. Among them, six were prepared using ultraviolet (UV) curing fiber reinforced plastics (FRPs) and six were prepared using ambient environment curing FRPs as controls. Filament wound composite pipes were used. Each section of pipe was 304.8 mm long with a 101.6 mm inner diameter. The wet lay‐up technique was used to prepare the test samples. The curing time for the UV curing samples was 40 minutes, while the curing time was 24 hours for the control samples. Both internal pressure tests and four‐point bending tests were conducted on the prepared samples. The test results show that the UV curing FRP wrapped composite pipe joints achieved nearly the same bending strength as the control samples. However, the internal pressure rating achieved by the UV curing FRP coupled joints was lower than that achieved by the control samples. A finite element analysis was conducted to understand the mechanism for the lowered internal pressure rating. Based on the test and the finite element analysis results, the UV curing FRP can be used in joining composite truss structures and composite frame structures. Suggestions were made to increase the internal pressure rating of UV curing FRP coupled composite pipes. Polym. Compos. 25:298–306, 2004. © 2004 Society of Plastics Engineers.
Processing‐properties relationship of sandwich panels with polypropylene‐core and polypropylene‐matrix composite skins
Authors: Passaro Alessandra , Corvaglia Paolo , Manni Orazio , Barone Luigi , Maffezzoli Alfonso
Published: June 2004

This paper reports on the development and the optimization of a thermoforming process (compression molding) for thermoplastic sandwich panels. The skins of the panels are fabricated from polypropylene (PP)/continuous glass fibers dry prepregs in the form of a commingled fabric. The use of two different types of core material has been used, a PP foam and a PP honeycomb. Additionally, two alternative methods for the thermoforming process have been analyzed, using either a one‐stage or a two‐stage process. In the one‐step process, skin molding and skin‐core bonding are carried out simultaneously. In the two‐stage process, the skins are first thermoformed and then bonded to the core as the second stage. The influence of the selected process parameters on the mechanical properties of the panels has been experimentally investigated, leading to the identification of the preferred processing conditions. Polym. Compos. 25:307–318, 2004. © 2004 Society of Plastics Engineers.
A comparative study on the influence of epoxy sizings on the mechanical performance of woven carbon fiber‐epoxy composites
Authors: Fernández B. , Arbelaiz A. , Valea A. , Mujika F. , Mondragon I.
Published: June 2004

In the present work the effect of epoxy sizings on the fracture behavior of woven carbon fiber tetrafunctional epoxy composites has been investigated. Three‐point flexural, short beam shear (SBS) and Mode‐II interlaminar fracture toughness (ENF) tests have been carried out. Wettability and Atomic Force Microscopy (AFM) studies have been performed on commercial sized, desized and 0.7 wt% TGDDM and 0.7 wt% DGEBA sized carbon fibers. Dynamic mechanical thermal analysis and Scanning Electron Microscopy (SEM) studies were also carried out on the different carbon fiber/epoxy composites. The used sizing treatments provided composites with improved mechanical properties due to the enhancement achieved in the fiber‐matrix adhesion. Polym. Compos. 25:319–330, 2004. © 2004 Society of Plastics Engineers.
Fiber orientation in multilayer tubes processed by a conical extruder
Authors: Sarioglu Alp , Hagstrand Per‐Ola , Månson Jan‐Anders E.
Published: June 2004

A new extruder design has been developed for the coextrusion of two‐layer annular sections. The extruder consists of a conical stator‐rotor‐stator assembly, which performs extrusion from each side of the rotor. Flow within this assembly is fully three‐dimensional, with helicoidal streamlines in the vicinity of the rotor and the die entry region. Fiber orientation is created in a circumferential direction by these helicoidal streamlines; close to the inner and outer surfaces of the tube, the fibers are parallel to the main extrusion direction, whereas in the mid‐thickness, they are oriented in the circumferential direction. It is demonstrated that the amount of orientation depends on rotor speed and die design. When using a short die and high rotor speed, an increased fraction of fibers are oriented in the circumferential direction. Polym. Compos. 25:331–341, 2004. © 2004 Society of Plastics Engineers.
Sterculia striata exudate polysaccharide: characterization, rheological properties and comparison with Sterculia urens (karaya) polysaccharide
Authors: Brito Ana Cristina F , Silva Durcilene A , de Paula Regina CM , Feitosa Judith PA
Published: June 2004

The exudate polysaccharide from Sterculia striata trees was investigated regarding its composition, structure and rheological properties and metal ion interactions. This polysaccharide contains galactose, rhamnose galacturonic and glucuronic acids as the main monosaccharide components. 13C NMR spectroscopy revealed that the anomeric composition is similar to that of Sterculia urens exudates, except for the presence of xylose, not identified in the latter polysaccharide. The empirical stiffness parameter B was determined for S striata (B = 0.043), suggesting that the polysaccharide exists in a semi‐rigid chain conformation, with no conformational change being demonstrated. Deacetylation led to a more flexible polymer chain (B = 0.058). The counter ion affinity of the polysaccharide aqueous solution was determined by intrinsic viscosity measurements, resulting in Al3+ > Ca2+ > Na+. Copyright © 2004 Society of Chemical Industry
Preparation and characterization of core–shell polystyrene–polydimethylsiloxane particles by seeded polymerization
Authors: Zou Mingxuan , Zhang Zhicheng , He Weidong , Ge Xuewu , Fan Fei
Published: June 2004

Nanometer scale particles of seed latex were successfully prepared by polymerization induced by gamma rays. By modification of the coupling agent 3‐methacryloxylpropyltrimethoxylsilane (MPS) at the surface of polystyrene (PSt) particles, polydimethylsiloxane (PDMS) was introduced outside the PSt particles and composite latex particles with a core–shell (PSt–PDMS) structure were successfully prepared. Because of the chemical bond linkage between the core and the shell, such a structure is stable. Direct evidence of the core–shell structure was observed by transmission electron microscopy (TEM). In addition the chemical bond linkage was confirmed by Fourier‐transfer infrared (FT‐IR) spectroscopy. An indirect proof of the core–shell structure was given by water absorption ratio determination of the different samples. Copyright © 2004 Society of Chemical Industry
Synthesis of poly(propylene glycol)‐grafted polyimide precursors and preparation of nanoporous polyimides
Authors: Do Jin‐Sek , Zhu Baoku , Han Sang Hyup , Nah Changwoon , Lee Myong‐Hoon
Published: June 2004

A novel approach to prepare a polyimide nanofoam was explored by using a polyimide precursor grafted with a labile poly(propylene glycol) (PPG) oligomer. The PPG‐grafted polyimide precursor, poly((amic acid)‐co‐(amic ester)), was synthesized via partial esterification of poly(amic acid) derived from pyromellitic dianhydride (PMDA) and 4,4′‐oxydianiline (ODA) with bromo‐terminated poly(propylene glycol) in the presence of K2CO3 in hexamethylphosphoramide and N‐methylpyrrolidone. The precursor polymer film was spin‐coated onto a glass substrate, then imidized at 200 °C under nitrogen, and subsequently the PPG graft was decomposed by heating the film at 300 °C for 9 h in air, resulting in the PMDA/ODA polyimide nanofoam. The precursor polymers, polyimides and foamed polyimides were characterized by a variety of techniques including 1H‐NMR spectroscopy, Fourier‐transform infrared (FT‐IR) spectroscopy, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The homogeneously distributed nano‐sized pores of 20–40 nm were observed by transmission electron microscopy (TEM) of the foamed polyimide. Copyright © 2004 Society of Chemical Industry
Fibre reinforcement of elastomers: nanocomposites based on sepiolite and poly(hydroxyethyl acrylate)
Authors: Bokobza L , Burr A , Garnaud G , Perrin MY , Pagnotta S
Published: June 2004

The reinforcement of poly(hydroxyethyl acrylate) provided by sepiolite particles has been analysed. Stress–strain measurements at equilibrium, as well as swelling experiments, were carried out on the unfilled and filled polymers. The state of dispersion of the filler was characterized by transmission electron microscopy. Moreover, an evaluation of chain orientation by infrared dichroism reveals a high orientation level in the filled system. The strong interaction between the two phases, combined with a good dispersion and a high shape factor of these clay particles, explain the improvement of the mechanical properties of the composites with respect to the pure polymer. Copyright © 2004 Society of Chemical Industry
Synthesis of new open‐chain alkoxyamines and their evaluation for nitroxide‐mediated radical polymerization
Authors: Nesvadba Peter , Bugnon Lucienne , Sift Rosemarie
Published: June 2004

New readily available open‐chain alkoxyamines have been synthesized and evaluated as unimolecular initiators for nitroxide‐mediated radical polymerization of styrene and n‐butyl acrylate. The observed moderate control of polymerization is explained by the low thermostability of the parent nitroxide. Copyright © 2004 Society of Chemical Industry
Mechanical and dynamic mechanical properties of nylon 66/montmorillonite nanocomposites fabricated by melt compounding
Authors: Yu Zhong‐Zhen , Yan Cheng , Yang Mingshu , Mai Yiu‐Wing
Published: June 2004

Nylon 66 nanocomposites were prepared by melt compounding of nylon 66 with organically modified montmorillonite (MMT). The organic MMT was pre‐modified with about 14 wt% of ammonium surfactant, much lower than the 35–46 wt% in most commercial organic MMT powders. Transmission electron microscope observation indicated that the MMT layers were well exfoliated in nylon 66 matrix. Dynamic mechanical analysis confirmed the constraint effect of exfoliated MMT layers on nylon 66 chains, which benefited the increased storage modulus, increased glass transition temperature and reduced magnitude of alpha relaxation peak. The effects of organic MMT loading levels on reinforcement and fracture behaviour of the nanocomposites were evaluated using tensile and three‐point bending tests. The addition of the organic MMT clearly increased Young's modulus and tensile strength but decreased ductility and fracture toughness of nylon 66. Copyright © 2004 Society of Chemical Industry