bluuebunny/crossref_metadata_2025_split huggingface dataset:
Wear of poly (methyl methacrylate) against a metallic surface in dry conditions
Authors: Geringer Jean , Forest Bernard , Combrade Pierre 
Published: March 2007

AbstractWear of Poly (methyl methacrylate), PMMA, against a metallic surface, AISI 316L stainless steel (SS) has been investigated in dry conditions. These materials have been used to simulate the degradation of the contact, femoral stem‐bone cement in the field of hip prosthesis. First of all, no significant wear was observed on the 316L SS. PMMA wear has been quantified: the energy wear coefficient, slope of the line, and wear volume according to the cumulated dissipated energy, don't depend on the normal load, FN. This energy analysis allows predicting the PMMA wear depth. According to the comparison between the measured dissipated energy and the energy breaking polymer chains, mechanical dissipated energy is used essentially to transform third body structure and to expel it from the contact between the two materials. Moreover, the experimental results have highlighted the stick‐slip phenomenon. Lastly, Attenuated Total Reflectance‐Fourier Transform InfraRed and Reflection Absorption‐Fourier Transform InfraRed have shown that PMMA debris configuration and conformation have changed after wear against 316L SS. The driving force of these changes seems to be the acid–base interactions between PMMA and hydroxyl groups of the SS surface. POLYM. ENG. SCI., 47:633–648, 2007. © 2007 Society of Plastics Engineers.
Computer simulation of reactive extrusion processes for free radical polymerization
Authors: Jia Yuxi , Zhang Guofang , Wu Lili , Sun Sheng , Zhao Guoqun , An Lijia 
Published: March 2007

AbstractThe reactive extrusion for polymerization is an integrated polymer processing technology. A new semi‐implicit iterative algorithm was proposed to deal with the complicated relationships among the chemical reaction, the macromolecular structure and the chemorheological property. Then the numerical computation expressions of the average molecular weight, the monomer conversion, and the initiator concentration were deduced, and the computer simulation of the reactive extrusion process for free radical polymerization was carried out, on basis of which reactive processing conditions can be optimized. POLYM. ENG. SCI., 47:667–674, 2007. © 2007 Society of Plastics Engineers.
An applicable electrospinning process for fabricating a mechanically improved nanofiber mat
Authors: Kim Geun Hyung , Han Houkseop , Park Jong Ha , Kim Wan Doo 
Published: March 2007

AbstractEngineered polymer scaffolds play an important role in tissue engineering. An ideal scaffold should have good mechanical properties and provide a biologically functional implant site. Considering their large surface area and high porosity, nanofibers have good potential as biomimetic scaffolds. However, the main shortcomings of scaffolds consisting of nanofibers are their mechanical inability to sustain a stress environment for neotissues and shape‐ability to form a variety of shapes and sizes. In this study, we produced design‐based poly (ε‐carprolactone) (PCL) nanofiber mats using an electrospinning method with various auxiliary electrodes and an x‐y moving system. To achieve stable initial solution at a nozzle tip of the electrospinning, various types of auxiliary electrodes were introduced. To characterize the effect of the electrodes in the electric‐field distribution near the nozzle tip, we calculated the electric field concentration factor and compared it with the experimental results. The nanofiber mat produced using the moving x‐y target system demonstrated orthotropic mechanical properties due to the fiber orientation, and human dermal fibroblasts seeded on the structure tended to grow according to nanofiber orientation. POLYM. ENG. SCI., 47:707–712, 2007. © 2007 Society of Plastics Engineers.
Highly Conjugated Organic Polymers as Heterogeneous Catalysts. I. Introduction and Literature Survey
Authors: Cooper David R. , Law Adrian M. G. , Tighe Brian J. 
Published: March 2007

AbstractThe use of highly conjugated organic polymers as heterogeneous catalysts is reviewed as part of a series of papers relating to their use in reactions involving oxides of nitrogen. The polymers which have been examined and the types of catalysed reaction so far recorded are described.In general the structural features, including extensive conjugation, which are considered important for catalytic activity and selectivity, are also responsible for their high thermal stability. The presence of hetero‐atoms, a high stable concentration of delocalised electrons and semiconductivity, have each been proposed as primary requisites for catalytic activity.
Gel permeation chromatographic evaluation of ethyl cellulose extrudates exhibiting “Sharkskin effect”
Authors: Brookshaw Alan P. , Hillman Donald E. , Paul John I. 
Published: March 2007

AbstractGel permeation chromatography has been utilised to investigate the molecular weight distribution of samples of ethyl cellulose which have exhibited extrusion defects corresponding to the phenomenon known as “sharkskin effect”. The results have indicated that a narrow molecular weight distribution is largely responsible for these defects. The effect of processing the polymer was to cause a fall in the number average molecular weight MN and weight average molecular weight MW although the distribution (MW/MN) did not change significantly. An improvement in the appearance of reprocessed material was attributed to an increase in the homogeneity of the sample, rather than an increase in the molecular weight distribution. Processing parameters could be altered to improve the finish of the extrudate, e.g. an increase in die temperature and a reduction in extrusion rate, but this is non‐viable on a production basis.Anomalous gel permeation chromatography results obtained using methylene chloride as solvent have been attributed to association due to residual hydroxyl groups in the ethyl cellulose.
High frequency mechanical properties of a polymer–surfactant filler system
Authors: Jones Ian H. , West George H. 
Published: March 2007

AbstractThe high frequency mechanical properties have been determined of ammonium perchlorate‐polyisobutane mixtures to which surfactants of various kinds have been added. A model has been suggested for the structure of the surfactant layer formed at the interface based on packing density and chain mobility as the controlling factors.
Dispersion polymerisation in organic media
Authors: Barrett Keith E. J. 
Published: March 2007

AbstractThe development of a technique for the direct preparation of polymer dispersions of controlled particle size in organic media is described. This method of dispersion polymerisation involves the polymerisation of a monomer dissolved in an organic liquid to produce insoluble polymer dispersed in the continuous phase. An amphipathic graft or block copolymer is used as the dispersant. The general features of the process, including the method used for stabilising the polymer dispersions and the mode of particle formation and growth, are reviewed.
Particulate reinforcement of polyacrylate elastomers. I. Introduction and Preparation of Materials
Authors: Blackley David C. , Sheikh Majid W. 
Published: March 2007

AbstractThe series of papers, of which this is the first, aims to demonstrate the importance of chemical reactions between filler particles and elastomer matrix in determining the physical properties of filled elastomers. A model system comprising small glass beads as the filler and crosslinked polyethylacrylate as the elastomer has been used. The beads themselves are inert towards the matrix during polymerisation, but the reactivity of the surfaces of the beads can be varied by suitable treatments. This paper describes techniques for fractionating the beads to give narrow particle‐size distribution, for preparing unfilled and filled elastomer sheets, and for preparing composites in which an elastomer sheet is polymerised in contact with a glass plate which may or may not have been previously subjected to surface treatment.
Polyester‐polyether block copolymers. I. Wide‐angle X‐ray diffraction studies of poly(hexamethylene terephthalate)/poly(oxytetramethylene) and related block polymers
Authors: Ghaffar Abdul , Goodman Isaac , Hall Ivan H. 
Published: March 2007

AbstractThe crystallisation and orientation of the individual structural components of poly(hexamethylene terephthalate)/poly(oxytetramethylene) block copolymers have been studied by wide‐angle X‐ray diffraction. The crystallisation behaviour in the unstretched state is determined by the proportions and molecular weights of the polyether blocks. For copolymers containing less than 60 wt% of polyether of m. w. ≯ 2000, only the polyester segments crystallise spontaneously, but with polyether m. w > 2000 two crystalline phases are formed. Similar behaviour was found in block polymers from other readily crystallising polyesters, but with non‐crystallising polyesters the polyether segments crystallised spontaneously.Moderate tensile deformation of the block copolymers from polyether of m. w. 2000 leads to the stress‐reversible highly oriented crystallisation of the polyether whilst the polyester remains undeformed. At higher extensions, irreversible orientation of the polyester segments occurs. The observations suggest that the polyester and polyether segments form discrete regions since otherwise homogeneous crystallisation should occur.
Kinetic simulation of single electron transfer–living radical polymerization of methyl acrylate at 25 °C
Authors: Monteiro Michael J. , Guliashvili Tamaz , Percec Virgil 
Published: March 2007

AbstractA mechanistic comparison of the ATRP and SET‐LRP is presented. Subsequently, simulation of kinetic experiments demonstrated that, in the heterolytic outer‐sphere single‐electron transfer process responsible for the SET‐LRP, the activation of the initiator and of the propagating dormant species is faster than of the homolytic inner‐sphere electron‐transfer process responsible for ATRP. In addition, simulation experiments suggested that in both polymerizations the rate of deactivation is similar. In SET‐LRP, the Cu(II)X2/L deactivator is created by the disproportionation of Cu(I)X/L inactive species, while in ATRP its concentration is mediated by the bimolecular termination. The combination of higher rate of activation with the creation of deactivator via disproportionation provides, via SET‐LRP, an ultrafast synthesis of polymers with very narrow molecular weight distribution at room temperature. SET‐LRP is mediated by a catalytic amount of Cu(0), and under suitable conditions, bimolecular termination is virtually absent. Kinetic and simulation experiments have also demonstrated that the amount of water available in commercial solvents and monomers is sufficient to induce the disproportionation of Cu(I)X/L into Cu(0) and Cu(II)X2/L and, subsequently, to change the polymerization mechanism from ATRP to SET‐LRP. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1835–1847, 2007.
Build‐up of carboxylic acids in polyethylene and their relation to off‐flavor and carbonyl index
Authors: Strandberg Clara , Albertsson Ann‐Christine 
Published: March 2007

AbstractOxidation of polyethylene (PE) gives a mixture of degradation products. Carboxylic acids are among the major ones. They are believed to cause off‐flavor in food and beverage packaging. Our previous research has shown that identification and use of indicator products gives earlier detection of oxidation in plastic materials. In the present study, the relation between off‐flavor in water extracts of PE and each of the carboxylic acids in the homologous series from propanoic to nonanoic acid were investigated. Also, a comparison between carbonyl index in solid PE and each of the carboxylic acids in the homologous series from propanoic to decanoic acid were examined. The amount of the carboxylic acids was assessed by head‐space solid‐phase microextraction (HS‐SPME) and gas chromatography–mass spectroscopy (GC‐MS). It was found that the amount of butanoic and hexanoic acid correlated well with the rated off‐flavor intensities in the water extracts. This confirmed earlier results on a linkage between these two carboxylic acids and highly rated off‐flavor intensities. Moreover, a relation between the build‐up of propanoic acid in the solid PE and carbonyl index was found. Hence, propanoic acid could be used as an indicator product for earlier oxidation detection in these PE materials. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1848–1859, 2007
New stage in living cationic polymerization: An array of effective Lewis acid catalysts and fast living polymerization in seconds
Authors: Aoshima Sadahito , Yoshida Tomohide , Kanazawa Arihiro , Kanaoka Shokyoku 
Published: March 2007

AbstractOur recent extensive research on Lewis acid catalysts with a weak base for the cationic polymerization of vinyl ethers led to unprecedented living reaction systems: fast living polymerization within 1–3 s; a wide choice of metal halides containing Al, Sn, Fe, Ti, Zr, Hf, Zn, Ga, In, Si, Ge, and Bi; and heterogeneously catalyzed living polymerization with Fe2O3. The use of added bases for the stabilization of the propagating carbocation and the appropriate selection of Lewis acid catalysts were crucial to the success of such new types of living polymerizations. In addition, the base‐stabilized living polymerization allowed the quantitative synthesis of star‐shaped polymers with a narrow molecular weight distribution via polymer‐linking reactions and the precision synthesis and self‐assembly of stimuli‐responsive block copolymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1801–1813, 2007.
Is tile drainage water representative of root zone leaching of pesticides?
Authors: Jacobsen Ole H , Kjær Jeanne 
Published: March 2007

AbstractGiven the methods presently available, determination of flux‐averaged concentrations of pesticides in structured soils is always a compromise. Most of the available methods entail major uncertainties and limitations. Tile drainage monitoring has several advantages, but the extent to which it is representative of overall leaching has been questioned because it comprises a mixture of water of different origins. This literature review evaluates whether drainage water pesticide concentrations are representative of root zone leaching of pesticides. As there are no reports quantifying the extent to which the flux‐averaged concentration of pesticides in drainage water differs from that found between the drains, evidence‐based conclusions cannot be drawn. Nevertheless, the existing literature does suggest that the concentration in drainage water does not always correspond to the concentration at drain depth between the drains; depending on the conditions pertaining, the concentrations may be higher or lower. As to whether the flux‐averaged concentration of pesticides in drainage water is representative of the interdrain concentration at drain depth it is concluded that (1) the representativeness of drainage water concentrations can be questioned on very well‐drained soils and on poorly drained soils with little capacity for lateral transport beneath the plough layer, (2) the conditions provided by relatively porous soils and moderate climatic conditions are conducive to the drainage water concentration being representative and (3) drainage water will be more representative in the case of weakly sorbed pesticides than for strongly sorbed pesticides. Used critically, it is thus believed that drainage water concentrations can serve to characterize the flux‐averaged concentration of pesticides at drain depth. However, the use of drainage water for determining average concentrations necessitates thorough investigation and interpretation of precipitation, percolation, drain outflow and concentration dynamics. Copyright © 2007 Society of Chemical Industry
Rock modeling and matching for autonomous long‐range Mars rover localization
Authors: Li Rongxing , Di Kaichang , Howard Andrew B. , Matthies Larry , Wang Jue , Agarwal Sanchit 
Published: March 2007

AbstractThis paper introduces the concept and design of a new integrated approach to long‐range autonomous Mars rover localization based on the incremental bundle adjustment and visual odometry technologies that have been individually experimented with during the 2003 Mars Exploration Rover mission. The design result indicates that a rover would have a varying performance in traversing from 7.5 to 118 m within one traverse leg under various scenarios including camera systems and traverse geometry, while maintaining the onboard rover localization accuracy at 1%. To implement the proposed integrated approach, the key is to develop autonomous cross‐site tie point selection algorithms for automatic generation of a sufficient number of high quality tie points to link all the images and to form the image network. New methods of rock extraction, rock modeling, and rock matching from multiple rover sites are developed to automate cross‐site tie point selection. Rocks are extracted from three‐dimensional ground points generated by stereo image matching, and then modeled using analytical surfaces such as hemispheroid, semiellipsoid, cone, and tetrahedron. Rocks extracted and modeled from two rover sites are matched by a combination of rock model matching and rock distribution pattern matching. The matched rocks are used as cross‐site tie points for a subsequent bundle adjustment. The presented results show that the proposed cross‐site tie point selection approach functions successfully for medium‐range (up to 26 m) traverse legs. © 2007 Wiley Periodicals, Inc.
Suppression of ovulation in Nile Hippopotamus (Hippopotamus amphibious) using melengestrol acetate‐treated feed or high dose Depo‐Provera injection
Authors: Wheaton Catharine J. , Joseph Sharon , Reid Kelly , Webster Tricia , Richards Mary , Forde Holly M. , Savage Anne 
Published: March 2007

AbstractAnalysis of fecal progestogen profiles during Depo‐Provera injection (1,200 mg; DEPO, Pfizer Inc., New York, NY), melengestrol acetate (MGA) in feed (2 or 3 mg/head/day), and a combination treatment (DEPO+MGA) are presented for nine captive female Nile hippos housed at Disney's Animal Kingdom in Florida. All tested treatments reduced fecal progestogen elevations successfully to durations consistent with prevention of ovulation for a portion of the treatment period. Percentage of treatment months with suppression of luteal phases indicative of ovulation was maximal for high‐dose MGA (91.7±13.9%) and DEPO+MGA (91.7±20.4%), followed by DEPO injection alone (69.2±13.9%) and low‐dose MGA (57.6±33.2%). Both 1,200 mg DEPO and low‐dose MGA (2.0 mg/day) treatments were insufficient to prevent an apparent seasonal breakthrough of ovarian activity from June–August 2002. Although luteal phases were observed, no females conceived during those months. Overall, in 133.5 treatment months with females housed with an adult male, one female conceived during the transition period between treatments. After cessation of contraceptive treatment, average latency to first normal ovarian cycle was 80.6±19.5 days (range = 22–179 days). Up to 12 months post‐treatment, however, successive cycles were often irregular with evidence of short periods of anovulation and shortened luteal phases in all females monitored. In conclusion, high dose and combination treatments were most successful in preventing progestogen increases indicative of ovulation in hippos. Zoo Biol 26:259–274, 2007. © 2007 Wiley‐Liss, Inc.
Longitudinal Assessment of Erythrocyte Fatty Acid Composition Throughout Pregnancy and Post Partum
Authors: Stewart Frances , Rodie Vanessa A. , Ramsay Jane E. , Greer Ian A. , Freeman Dilys J. , Meyer Barbara J. 
Published: March 2007

AbstractTransfer of fatty acids from mother to fetus during pregnancy is a requirement for optimal fetal growth. We report a longitudinal study of full maternal erythrocyte fatty acid profile assessed at each trimester of pregnancy [mean 12.5 (range 8–14), 26.1 (24–28) and 35.5 (33–38) weeks’ gestation] and in the post partum period [18.1 (12–26) weeks]. The study recruited healthy women (n = 47) from routine antenatal clinics at the Princess Royal Maternity Unit, Glasgow, Scotland. There were increases in 16:1n7 (22%, p = 0.0005), 24:1n9 (13%, p = 0.0032), 22:5n6 (25%, p = 0.0003), 18:3n3 (41%, p = 0.0007) and 22:6n3 (20%, p = 0.0005) concentrations during pregnancy. The greatest increases took place between gestations at sampling of 12.5 and 26.1 weeks. The change in 16:1n7 concentration between gestations at sampling of 12.5 and 35.3 weeks was negatively associated with maternal booking body mass index (r = −0.40, p = 0.006). The change in 22:6n3 concentration was correlated with the change in 24:1n9 (r = 0.70, p < 0.001). In samples taken four months post partum, 14:0 concentration was lower (29%, p = 0.0002) and 24:0 concentration (15%, p = 0.0009) and n6/n3 ratio (11%, p = 0.0019) were higher than at a gestation at sampling of 12.5 weeks. In conclusion, several fatty acids are specifically mobilised during pregnancy. The correlation between maternal 22:6n3 and 24:1n9 suggests that mobilisation of these fatty acids may be coordinated. The inverse relationship between 16:1n7 and maternal central obesity warrants further investigation.
Folate deprivation promotes mitochondrial oxidative decay: DNA large deletions, cytochromecoxidase dysfunction, membrane depolarization and superoxide overproduction in rat liver
Authors: Chang Chun-Min , Yu Chu-Ching , Lu Hsin-Te , Chou Yi-Fang , Huang Rwei-Fen S. 
Published: March 2007

Little is known about the biological effect of folate in the protection against mitochondrial (mt) oxidative decay. The objective of the present study was to examine the consequence of folate deprivation on mt oxidative degeneration, and the mechanistic link underlying the relationship. Male Wistar rats were fed with an amino acid-defined diet containing either 8 (control) or 0 (folate-deficient, FD) mg folic acid/kg diet. After a 4-week FD feeding period, significant elevation in oxidative stress was observed inside the liver mitochondria with a 77 % decrease in mt folate level (P < 0·001), a 28 % reduction in glutathione peroxidase activity (P = 0·0333), a 1·2-fold increase of mt protein carbonyls (P = 0·0278) and an accumulated 4834 bp large-scale deletion in mtDNA. The elicited oxidative injuries in FD liver mitochondria were associated with 30 % reduction of cytochromecoxidase (CcOX) activity (P = 0·0264). The defective CcOX activity in FD hepatocytes coincided with mt membrane potential dissipation and intracellular superoxide elevation. Exposure of FD hepatocytes to pro-oxidant challenge (32 μm-copper sulphate for 48 h) led to a further loss in CcOX activity and mt membrane potential with a simultaneous increase in superoxide production. Preincubation of pro-oxidant-treated FD hepatocytes with supplemental folic acid (10–1000 μm) reversed the mt oxidative defects described earlier and diminished superoxide overproduction. Increased supplemented levels of folic acid strongly correlated with decreased lipid peroxidation (γ − 0·824,P = 0·0001) and protein oxidative injuries (γ − 0·865,P = 0·0001) in pro-oxidant-challenged FD liver mitochondria. Taken together, the results demonstrated that folate deprivation induces oxidative stress in liver mitochondria, which is associated with CcOX dysfunction, membrane depolarization and superoxide overproduction. The antioxidant activity of supplemental folic acid may partially, if not fully, contribute to the amelioration of pro-oxidant-elicited mt oxidative decay.