bluuebunny/crossref_metadata_2025_split huggingface dataset:
The influence of resin chemistry on a dental composite's biodegradation
Authors: Finer Y. , Santerre J. P. 
Published: March 2004

AbstractPrevious work reported that commercial dental composite resins containing a urethane‐modified bisGMA (bisphenylglycidyl dimethacrylate)/TEGDMA (triethylene glycol dimethacrylate) (ubis) based monomer system showed a 10‐fold reduction in the release of a bisGMA‐derived product, bishydroxypropoxyphenyl propane (bisHPPP), as compared with that found for bisGMA/TEGDMA (bis) based composites after incubation with cholesterol esterase (CE). Unfortunately, these materials also differed substantially in filler type and content, making it impossible to directly relate any specific parameter to the differences in biodegradation levels. By controlling for filler content and type, the current study will seek to probe the biomolecular interactions between composite resin chemistry and esterase activity in order to help explain the observed differences in biodegradation levels between the ubis and bis resin systems. After 32 days of incubation, buffer and CE solutions were analyzed for degradation products using high‐performance liquid chromatography, UV spectroscopy, and mass spectrometry. Both materials were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and X‐ray photoelectron spectroscopy. In the CE groups, the ubis system showed a 2.6‐ to 86‐fold reduction (dependent on the product) in the amount of isolated products relative to the bis system (p < 0.01). Scanning electron microscopy data also demonstrated the relative stability of the ubis system and X‐ray photoelectron spectroscopy analysis showed a higher content of the ester bond at the surface of the bis samples. Fourier transform infrared data showed that both resins had similar conversions. Because both systems were identical except for their monomer systems, it was concluded that changes in biostability were associated with chemistry. Crosslinking, hydrophobicity, and solubility all relate to ubis's pro‐stability. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 69A: 233–246, 2004
Cell responses to BMP‐2 and IGF‐I released with different time‐dependent profiles
Authors: Raiche A. T. , Puleo D. A. 
Published: March 2004

AbstractDuring wound healing, growth factors are expressed in time‐dependent amounts. Constant delivery of biomolecules, however, is often used to influence cell and tissue behavior. In the present studies, a crosslinked gelatin‐coating system was used to deliver bone morphogenetic protein 2 (BMP‐2) or insulin‐like growth factor (IGF‐I) to three types of mesenchymal cells with three temporally varying release profiles. The “early” delivery profile released most of the growth factor within the first 2 days. The “pseudo‐zero‐order” profile approximated constant rate of delivery for about 5 days. The “late” delivery profile released most of the growth factor after about 5 days. Early delivery of IGF‐I had the greatest effect on mitogenesis of SaOS‐2 human osteosarcoma cells with a secondary effect noted nearly 5 days after delivery was completed. Late delivery of BMP‐2 resulted in greatest alkaline phosphatase (AP) activity in mouse pluripotent C3H10T1/2 cells. Rat bone marrow stromal cells (BMCs) responded to all delivery profiles of BMP‐2, with the duration of elevated AP activity increasing as the amount of BMP‐2 delivered increased. In addition to an early increase in AP activity, late release also stimulated BMCs over a longer portion of the culture period. BMCs responded similarly to SaOS‐2 cells when seeded on early IGF‐I delivery coatings, increasing AP activity after delivery had ended. Overall, these studies further show the importance of delivery profile, specifically the characteristics of time and concentration, on cell and tissue responses. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 69A: 342–350, 2004
In vitro behavior of osteoblastic cells cultured in the presence of pseudowollastonite ceramic
Authors: Sarmento Carlos , Luklinska Zofia B. , Brown Lindsey , Anseau Michel , De Aza Piedad N. , De Aza Salvador , Hughes Francis J. , McKay Ian J. 
Published: March 2004

AbstractPseudowollastonite ceramic (psW) is a bioactive ceramic that binds to bone when implanted in vivo and may be useful for the treatment of skeletal defects. However, there have been no studies that examined the interaction between psW and osteoblastic cells in vitro. This study investigated the suitability of psW as a substratum for cell attachment and the ability of the material to effect osteoblasts at a distance from the material surface. Fetal rat calvarial cells were plated onto the ceramic and examined by scanning electron microscopy. The findings reported show that cells attached and proliferated on the surface to the ceramic. Attachment by cells to the material can be enhanced by preincubation of psW in serum or media containing fibronectin. The adhesion of cells can be inhibited by addition of GRGDS peptides suggesting that adhesion to psW is mediated by integrin binding to adsorbed proteins. To study the effects of psW at a distance, cells were cultured in the presence but not in direct contact with the material. Subsequent changes in proliferation, alkaline phosphatase expression, and bone nodule formation were assessed. Cells grown in wells containing psW demonstrated an increase in both the rate and total numbers of bone nodules formed, although there were no differences in proliferation or alkaline phosphatase expression. Overall, these results suggest that psW is biocompatible and osteoconductive. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 69A: 351–358, 2004
Influence of pores created by laser superfinishing on osseointegration of titanium alloy implants
Authors: Stangl R. , Pries A. , Loos B. , Müller M. , Erben R. G. 
Published: March 2004

AbstractThe aim of this study was to assess the osseointegration of copper vapor laser–superfinished titanium alloy (Ti6Al4V) implants with pore sizes of 25, 50, and 200 μm in a rabbit intramedullary model. Control implants were prepared by corundum blasting. Each animal received all four different implants in both femora and humeri. Using static and dynamic histomorphometry, the bone–implant interface and the peri‐implant bone tissue were examined 3, 6, and 12 weeks postimplantation. Among the laser‐superfinished implants, total bone–implant contact was smallest for the 25‐μm pores, and was similar for 50‐ and 200‐μm pore sizes at all time points. However, all laser‐superfinished surfaces were inferior to corundum‐blasted (CB) control implants in terms of bone–implant contact. Within the 12‐week study period, remodeling of woven bone initially formed within pores occurred only in the implants with 200‐μm pores. Implants with 25‐μm pores showed the highest amount of peri‐implant bone volume at all time points, indicating that the amount of peri‐implant bone was not correlated with the quality of the bone–implant interface. At 3 and 6 weeks postsurgery, we did not find any differences in mineral apposition rates or bone formation rates between the various implant surfaces. However, the peri‐implant bone formation rate at the end of the trial was 70 and 62% higher in implants with 50‐ and 200‐μm pores compared with CB implants, respectively. We conclude that, although laser‐superfinished implants were not superior to CB control implants in terms of osseointegration, our study has provided further insights into the mechanisms of bone remodeling within pores of various sizes, and may form a basis for future experiments to design optimal implant surfaces with the help of modern laser technology. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 69A: 444–453, 2004
Patterns of variation in the phalangeal formulae of land tortoises (Testudinidae): Developmental constraint, size, and phylogenetic history
Authors: Crumly C. R. , Sánchez‐Villagra M. R. 
Published: March 2004

AbstractDocumentation of variation in phalangeal formulae in land tortoises combined with ontogenetic information from turtles in general were used, in a phylogenetic context, to infer the potential effect of size and developmental constraints upon patterns of morphological variation. A sample of 201 specimens and published illustrations of 37 tortoise species were examined, representing all but one living genera and most species of the Testudinidae. Specimens were either articulated dry skeletons or preserved animals that were x‐rayed. The patterns of digital and phalangeal loss in tortoises were predicted from developmental studies of the manus and pes in other turtles. If a digit is lost, it is the first digit, which is the last one to develop. If a digit has a single phalanx, it is usually the fifth digit. The primitive phalangeal formula for land tortoises is probably 2–2–2–2–1, the most common pattern found in living testudinid species. The presence of a second phalanx in the fifth digit evolved independently many times and usually in large tortoises. Such additions were interpreted as instances of peramorphosis. Many small tortoises have a full complement of digits (five) and phalanges (two in each digit); nevertheless, phalangeal and digital loss is associated with small size. Small and medium size tortoises exhibit greater variation in phalangeal number than do large tortoises. We hypothesize that epigenetic processes, and not simply adaptation, played a major role in the evolution of the variation in phalangeal formulae in tortoises. J. Exp. Zool. (Mol. Dev. Evol.) 302B:134–146, 2004. © 2004 Wiley‐Liss, Inc.
Tyrosine hydroxylase and dopamine transporter expression following 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine‐induced neurodegeneration of the mouse nigrostriatal pathway
Authors: Jakowec Michael W. , Nixon Kerry , Hogg Elizabeth , McNeill Tom , Petzinger Giselle M. 
Published: March 2004

AbstractAdministration of the neurotoxicant 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) to C57BL/6 mice targets nigrostriatal dopaminergic neurons, leading to cell death and the depletion of striatal dopamine. After MPTP lesioning in young adult mice, surviving nigrostriatal dopaminergic neurons display robust and reproducible return of striatal dopamine weeks to months after injury. Thus, the mouse provides an excellent model with which to investigate the mechanisms underlying neuroplasticity of the nigrostriatal system following neurotoxic injury. The purpose of this study was to analyze proteins and mRNA transcripts of genes involved in dopamine biosynthesis (tyrosine hydroxylase; TH) and uptake (dopamine transporter; DAT) with regard to time course (7–90 days) after MPTP lesioning. Molecular analysis using immunohistochemistry and Western immunoblotting techniques demonstrated an increase in striatal TH by 30–60 days postlesioning that returned to near‐control (prelesioned) levels by 60–90 days. In situ hybridization histochemistry indicated that this increase in TH protein might be due in part to increased TH mRNA expression in surviving nigrostriatal dopaminergic neurons. Analysis of TH protein at 7, 30, 60, and 90 days postlesioning with two‐dimensional polyacrylamide gel electrophoresis in conjunction with Western immunoblotting revealed altered TH protein isoforms migrating at isoelectric points different from those of the native isoform. In contrast to TH protein, which returned to prelesioned levels by 60 days, DAT protein analysis showed that increased expression of striatal DAT protein did not return to near‐prelesion levels until 90 days postlesioning. These results suggest that TH and DAT may differ in their time course of expression in surviving dopaminergic neurons and may play a role in mediating the return of striatal dopamine. © 2004 Wiley‐Liss, Inc.
Effect of mating surface on the high temperature wear of 253 MA alloy
Authors: Roy M. , Pauschitz A. , Wernisch J. , Franek F. 
Published: March 2004

AbstractThe wear behaviour of metallic material is influenced by the friction force, which in turn, is governed by the hardness and oxidation kinetics of the mating surface. In view of this, present investigation is undertaken to find the influence of mating surface on the high temperature wear of 253 MA alloy. This alloy is developed for high temperature application. In this work 253 MA alloy is made to slide against two different types of counter face material, namely 100Cr6 steel and PM 1000 alloy, at five different temperatures. 100Cr6 steel gets soften with increase of temperature whereas PM 1000 alloy retains its strength even at high temperature. The friction coefficient and the thickness loss of 253 MA alloy is measured and compared against both variety of mating surfaces as function of temperatures. The morphology of the worn surfaces and the transverse section of the worn surfaces are examined under scanning electron microscope (SEM) to identify the material removal mechanisms. The results showed that the friction coefficient of test material against PM 1000 alloy is around 40% higher than the friction coefficient against 100Cr6 steel. The transverse section of the worn surface showed presence of a transfer layer, mechanically mixed layer and composite layer, which govern the wear behaviour particularly at elevated temperature. The chemical characteristics of these layers are dependent on the test temperature and the counter face material.
Voltammetric behaviour of an archeaological bronze alloy in aqueous chloride media
Authors: Souissi N. , Bousselmi L. , Khosrof S. , Triki E. 
Published: March 2004

AbstractThe interface archaeological bronze alloy‐chloride media was characterized by using linear sweep rate cyclic voltammetry. The electrochemical behaviour of the Cu‐Sn alloy being different from pure copper and pure tin. In fact, the voltammograms show an anodic peak and two cathodic peaks. Surface examination revealed a compact layer which spread over the ancient material. The influence of different parameters such as scan rate, chloride concentration and repetitive cycling on the voltammetric response of the archaeological bronze was also studied. The results indicate that patina layer formation is a spreading process over the electrode surface leaving only small pores. Diffusion of the halide controls the growing rate of this layer. Two other anodic peaks are evidences when potential cycling increases. The oxidation became more difficult as a result of a constant layer thickness.
An Error‐in‐Variables Method for Determining Reactivity Ratios by On‐Line Monitoring of Copolymerization Reactions
Authors: Sünbül Didem , Çatalgil‐Giz Huceste , Reed Wayne , Giz Ahmet 
Published: March 2004

AbstractSummary: A new error‐in‐variables method was developed to estimate the reactivity ratios in copolymerization systems. It brings the power of automatic, continuous, on‐line monitoring of polymerization (ACOMP) to copolymerization calculations. In ACOMP systems, monomer and polymer concentrations are measured by the monitoring of two independent properties of the system. The reactivity ratios are found by taking into account errors in the monomer concentrations determined from measurements and from calibration of the instruments. All the error sources are taken into account according to the error‐in‐variables method, and their effects are reflected in determining the confidence intervals of the reactivity ratios by the usual error propagation technique.Distribution of concentrations [a] and [b] for the simulated experiment I. Random errors are 1% of the initial value in both observed variables.imageDistribution of concentrations [a] and [b] for the simulated experiment I. Random errors are 1% of the initial value in both observed variables.
Development of a Coupled Viscosity‐Polymerization Model for the Synthesis of High Solids‐Low Viscosity Latexes
Authors: do Amaral Marcelo , van Es Steven , Asua José M. 
Published: March 2004

AbstractSummary: The development of a model‐assisted methodology for the synthesis of high solids‐low viscosity latexes is presented. A simplified polymerization model for systems with a polydisperse particle size distribution, PSD, was developed. The polymerization model was then coupled with an equation for the computation of the viscosity. Their combination resulted in a powerful tool that helped to screen strategies for the synthesis of high solids‐low viscosity latexes. Furthermore, using the model‐assisted methodology it was possible to determine the workable viscosity boundary for a given formulation. The evolution of the viscosity with the volume fraction was calculated for different polymerization strategies.Particle size distribution evolution of Simulation 1. Large particles (•) and small particles (□).imageParticle size distribution evolution of Simulation 1. Large particles (•) and small particles (□).
Effect of Caustic Addition in Epoxy Polymerization Process: A Single and Multi‐Objective Evolutionary Approach
Authors: Raha Sasanka , Majumdar Saptarshi , Mitra Kishalay 
Published: March 2004

AbstractSummary: An epoxy polymerization process is studied in semi‐batch mode. Caustic has a very critical influence on epoxy polymerization process, which is modeled as a set of highly nonlinear coupled ODE's (ordinary differential equations). Owing to the highly complicated, nonlinear domain of analysis, “Differential Evolution (DE)” and “Genetic Algorithm (GA)” are used as optimization tools to identify the $\overline M _{\rm n}$‐PDI Pareto set and study the best operating strategy with respect to NaOH addition. The moment of various oligomeric components during the semi‐batch polymerization is also presented for a better understanding of the process. This study demonstrates the potential of evolutionary optimization algorithm to identify various operating philosophies of a semi‐batch epoxy reactor for a targeted product quality.Pareto plot for epoxy polymerization process with intermediate NaOH addition varying from 0.0 to 1.0 kmol · m−3.imagePareto plot for epoxy polymerization process with intermediate NaOH addition varying from 0.0 to 1.0 kmol · m−3.
Modeling of Ethylene Polymerization Kinetics over Supported Chromium Oxide Catalysts
Authors: Choi Kyu Yong , Tang Shihua , Yoon Won Jung 
Published: March 2004

AbstractSummary: Silica supported chromium oxide catalysts have been used for many years to manufacture polyethylene and they still account for more than 50% of world production of high‐density polyethylene. Along with its commercial success, the catalytic mechanism and polymerization kinetics of silica supported chromium oxide catalysts have been the subject of intense research. However, there is a lack of modeling effort for the quantitative prediction of polymerization rate and polymer molecular weight properties. The chromium oxide catalyzed ethylene polymerization is often characterized by the presence of an induction period followed by a steady increase in polymerization rate. The molecular weight distribution is also quite broad. In this paper, a two‐site kinetic model is developed for the modeling of ethylene polymerization over supported chromium oxide catalyst. To model the induction period, it is proposed that divalent chromium sites are deactivated by catalyst poison and the reactivation of the deactivated chromium sites is slow and rate controlling. To model the molecular weight distribution broadening, each active chromium site is assumed to have different monomer chain transfer ability. The experimental data of semibatch liquid slurry polymerization of ethylene is compared with the model simulations and a quite satisfactory agreement has been obtained for the polymerization conditions employed.Polymerization rates at different reaction temperatures: symbols – data, lines – model simulations.imagePolymerization rates at different reaction temperatures: symbols – data, lines – model simulations.
Cover Picture: Macromol. Theory Simul. 2/2004
Authors: Meier Robert J. , Koglin Eckhard 
Published: March 2004

Cover: The picture on the cover shows a theoretician, noting that different computational methods yield very different results, asking himself what result to believe, and in particular for what reason. It illustrates a dilemma when studying families of real‐life catalytic systems by quantum calculations, for which high‐level calculations are computationally prohibitive. The experimental chemist is awaiting the prediction by the theoretician.Further details can be found in the Full Paper by R. J. Meier* and E. Koglin on page 133.
Lack of mutations in DJ‐1 in a cohort of Taiwanese ethnic Chinese with early‐onset parkinsonism
Authors: Lockhart Paul J. , Bounds Rebecca , Hulihan Mary , Kachergus Jennifer , Lincoln Sarah , Lin Chin‐Hsien , Wu Ruey‐Meei , Farrer Matthew J. 
Published: March 2004

AbstractRecently, mutations in DJ‐1 (PARK7) were described as a novel cause of early‐onset parkinsonism. We analysed the DJ‐1 gene in a cohort of patients originating from Taiwan with early‐onset Parkinson's disease; 41 subjects were clinically and genetically examined. These patients were evaluated previously for the presence of parkin mutations (PARK2) and were found to be negative. The entire DJ‐1 open‐reading frame was amplified from cDNA, analysed for size alterations indicative of mutations affecting splice motifs, and sequenced to identify coding variants. In addition, we developed quantitative polymerase chain reaction assays to examine the genomic copy number of DJ‐1 exons. No potential splice site mutations, coding sequence alterations, or exon deletion/duplications were detected. Our results and previous studies suggest that alterations to DJ‐1 are not a common cause of early‐onset Parkinson's disease and other causes, genetic and/or environmental, remain to be identified. © 2004 Movement Disorder Society
A complete 1H and 13C NMR data assignment for the diterpene methyl (−)‐zanzibarate by 2D spectroscopy and NOE experiments
Authors: Imamura P. M. , Miranda P. C. M. L. , Giacomini R. A. 
Published: March 2004

AbstractThe 1H and 13C NMR spectra of methyl (−)‐zanzibarate (1), an ent‐labdanic diterpene isolated from the epicarp of Hymenaea courbaril var. altissima (Leguminosaea, Cesalpinoideae, Detariae), was fully assigned by COSY experiments, 13C/1H shift correlation diagrams and NOE experiments. Copyright © 2004 John Wiley & Sons, Ltd.
Structural properties of perfluorinated linear alkanes: a 19F and 13C NMR study of perfluorononane
Authors: Schwarz Roman , Seelig Joachim , Künnecke Basil 
Published: March 2004

AbstractLiquid perfluorocarbons exhibit unique physical–chemical characteristics such as extraordinary stability, combined hydrophobia and lipophobia, low surface tension and a capacity to carry large quantities of gas. They have found widespread use in industry, medicine and biology even though the molecular origin of these properties is not fully understood. The objective of the present work was to elucidate the physical behavior of perfluorinated linear alkanes by investigating their intramolecular electronic environment using 13C and 19F NMR techniques in combination with theoretical calculations of molecular orbitals. Particular advantage was taken of 19F–19F through‐space couplings, which led us to propose a molecular model in which delocalized p‐electrons of the fluorines cover the entire surface of the molecule in two pairs of intertwined helices. Experimental data are presented for n‐perfluorononane and supported by corresponding measurements with shorter and longer perfluorinated alkanes. Copyright © 2004 John Wiley & Sons, Ltd.