bluuebunny/crossref_metadata_2025_split huggingface dataset:
Temporal squama shape in fossil hominins: Relationships to cranial shape and a determination of character polarity
Authors: Terhune Claire E. , Deane Andrew S. 
Published: July 2008

AbstractIn 1943, Weidenreich described the squamosal suture of Homo erectus as long, low, and simian in character and suggested that this morphology was dependent upon the correlation between the size of the calvarium and the face. Many researchers now consider this character to be diagnostic of H. erectus. The relationship between cranial size and shape and temporal squama morphology, however, is unclear, and several authors have called for detailed measurements of squamosal variation to be collected before any conclusions are drawn regarding the nature of the morphology observed in H. erectus. Thirteen fossil and extant taxa were examined to address two questions: 1) Are size and shape of the temporal squama correlated with cranial vault morphology? and 2) Is the H. erectus condition plesiomorphic? To answer these questions, measurements were collected and indices were calculated for squamosal suture height, length, and area in relation to metric variables describing cranial size and shape. A two‐dimensional morphometric study was also completed using High Resolution‐Polynomial Curve Fitting (HR‐PCF) to investigate correlations between curvature of the squamosal suture and curvature of the cranial vault. Results of both analyses indicate that squamosal suture form is related to cranial size and shape. Furthermore, the plesiomorphic condition of the squamosal suture for hominins was identified as high and moderately arched; this condition is retained in H. erectus and is distinct from the great ape condition. It is suggested that this similarity is the result of increased cranial length without a corresponding increase in cranial height. Am J Phys Anthropol, 2008. © 2008 Wiley‐Liss, Inc.
The mineralized osteocyte: A living fossil
Authors: Bell Lynne S. , Kayser Mike , Jones Chris 
Published: July 2008

AbstractWe report here on an enigmatic and biologically mysterious event in which a single cell, the osteocyte, mineralizes in vivo and in this process the cell's organelles, cytoskeleton and membrane, are mineralized in a dying state. That the bony lacuna in which the lone osteocyte resides becomes infilled with mineral in vivo is not a new observation and was noted by early microscopists. This study has applied scanning and transmission electron microscopy to modern, archaeological, and fossil bone to investigate the mineral and organic structure and content of this cell. The results from this study revealed that within this mineral lies a visibly identifiable cell, which has an apoptotic‐like morphology. The mechanisms by which this cell mineralizes are so intimate chemically that remnant cell organelles, membranes, cytoskeleton, and potentially nucleic bodies are morphologically identifiable. We have further identified mineralized osteocytes surviving in archaeological and fossil mammal bone up to 5 million years BP. The significance of our findings demonstrates that a single cell may itself mineralize in vivo via an unknown set of biochemical events. Importantly, the location and survival of extra cellular and cellular proteins, including nuclear and mitochondrial DNA in bone after death, has been an area of some speculation, and this unique fossil cell provides a preservation locus within human and mammalian bone, which might be fruitfully targeted in future biomolecular studies. Am J Phys Anthropol, 2008. © 2008 Wiley‐Liss, Inc.
Brief Communication: Latent toxoplasmosis and salivary testosterone concentration—Important confounding factors in second to fourth digit ratio studies
Authors: Flegr Jaroslav , Lindová Jitka , Pivoñková Věra , Havlíček Jan 
Published: July 2008

AbstractA sexually dimorphic characteristic, the second to fourth digit ratio (2D:4D ratio), has been shown to reflect the prenatal concentration of sex steroid hormones and to correlate with many personality, physiological, and life history traits. The correlations are usually stronger for the right than the left hand. Most studies have shown that the 2D:4D ratio does not vary with age or postnatal concentration of sex steroid hormones. Recently, a strong association between left hand 2D:4D ratio and infection with a common human parasite Toxoplasma has been reported. We hypothesized that the confounding effect of Toxoplasma infection on left hand 2D:4D ratio could be responsible for the stronger association between different traits and right hand rather than left hand 2D:4D ratio. This confounding effect of toxoplasmosis could also be responsible for the difficulty in finding an association between 2D:4D ratio and age or postnatal steroid hormone concentration. To test this hypothesis, we analyzed the association between sex and age and 2D:4D ratio in a population of 194 female and 106 male students with and without controlling for the confounding variables of Toxoplasma infection and testosterone concentration. Our results showed that the relationship between age and sex and 2D:4D ratio increased sharply when Toxoplasma infection and testosterone concentration were controlled. These results suggest that left hand 2D:4D ratio is more susceptible to postnatal influences and that the confounding factors of Toxoplasma infection, testosterone concentration and possibly also age, should be controlled in future 2D:4D ratio studies. Because of a stronger 2D:4D dimorphism in Toxoplasma‐infected than Toxoplasma‐free subjects, we predict that 2D:4D ratio dimorphism as well as right hand/left hand 2D:4D ratio dimorphism will be higher in countries with a high prevalence of Toxoplasma infection than in those with a low prevalence. Am J Phys Anthropol, 2008. © 2008 Wiley‐Liss, Inc.
Halbleiterdrähte und ‐bänder als flexible Bauelemente für die Hochleistungselektronik
Authors: Baca Alfred J. , Ahn Jong‐Hyun , Sun Yugang , Meitl Matthew A. , Menard Etienne , Kim Hoon‐Sik , Choi Won Mook , Kim Dae‐Hyeong , Huang Young , Rogers John A. 
Published: July 2008

AbstractIn diesem Aufsatz werden die Eigenschaften und die Herstellung anorganischer Halbleitermaterialien behandelt, die als aktive Elemente für Hochleistungstransistoren und Stromkreise in großflächigen, flexiblen und biegestabilen elektronischen Bauteilen eingesetzt werden können. Die Realisierung hoher Leistungsdichten auf Niedertemperaturpolymeren ist eine technische Herausforderung für die Makroelektronik. Die Produktion qualitativ hochwertiger anorganischer Materialien in Form von Drähten, Bändern, Membranen, Schichten und Stäben nach “Bottom‐up”‐ und “Top‐down”‐Verfahren und die Strategien zur Montage dieser Bauteile auf plastischen Substraten werden daher besonders betont. Wichtige Fortschritte auf dem Gebiet dehnbarer und biegsamer anorganischer Halbleitermaterialien und die Grundlagen dieser mechanischen Stabilität sowie dreidimensionale Konstruktionen werden diskutiert. Abschließend werden die Perspektiven dieses vielversprechenden Forschungsfelds beleuchtet.
Die optische Aktivität achiraler Substanzen
Authors: Claborn Kacey , Isborn Christine , Kaminsky Werner , Kahr Bart 
Published: July 2008

AbstractAusgerichtete achirale Molekule und Kristalle mit D2d‐Symmetrie oder einer der nichtenantiomorphen Untergruppen S4, C2v oder Cs können beim Durchstrahlen in einer beliebigen Richtung eine Drehung der Schwingungsebene von linear polarisiertem Licht bewirken. Dies ist in der Kristalloptik eine unangefochtene Tatsache, der Unterricht für Studenten der organischen Chemie vermittelt hingegen eine widersprüchliche Ansicht. Der vorliegende Kurzaufsatz verschafft einen Überblick über Messungen und Rechnungen zu den chiroptischen Eigenschaften einiger achiraler Substanzen und Kristalle. Prototypisch für Verbindungen, die nach van't Hoff optisch inaktiv sein sollten, sind Methanderivate mit vier identischen Liganden, die durch Spiegelebenen in Beziehung stehen. Die Untersuchung der optischen Aktivität einfacher achiraler Verbindungen wie H2O und NH3 vermittelt weitreichende chiroptische Gesetzmäßigkeiten, die oft im Zusammenhang mit chiralen Stoffen übersehen werden. Hier wird anhand gruppentheoretischen Überlegungen, des Transformationsverhaltens von Tensoren und intuitiver Skizzen gezeigt, warum einige achirale azentrische Verbindungen optisch aktiv sind, andere hingegen nicht.
The Road to Non‐Enzymatic Molecular Networks
Authors: Dadon Zehavit , Wagner Nathaniel , Ashkenasy Gonen 
Published: July 2008

AbstractThis Minireview gives an overview of recent progress in the design and analysis of chemical systems that utilize template‐directed autocatalytic and cross‐catalytic processes as a means of wiring dynamically interacting molecules. Synthetic networks comprising two to nine replicating species are discussed. It is shown that for larger systems, more catalytic pathways must be manipulated to control the entire network topology and specific functionality of the individual species or subnetworks. Cellular biochemistry is an example of a natural functional molecular network; synthetic self‐organized networks can provide additional models of complex systems.
Preparation and pH‐sensitivity of polyacrylonitrile (PAN) based porous hollow gel fibers
Authors: Shen Xinyuan , Ji Yali , Wang Jue 
Published: July 2008

AbstractPolyacrylonitrile based porous hollow gel fibers were prepared from PAN hollow fibers by oxidation and subsequent alkaline treatment. Fourier‐transform infrared (FTIR), X‐ray diffraction, and scanning electron microscope (SEM) analyses showed that the PAN porous hollow gel fiber was a kind of amphoteric fiber due to the combination of cationic groups of pyridyl and anionic groups of carboxyl; after gelation the hollow channel and finger‐like pores on the fiber walls were conserved. The effects of cyclization reaction degree, alkaline solution concentration, and alkaline treatment time on the mechanical properties or pH‐sensitive behavior of the porous hollow gel fibers were investigated. The elongation/contraction behavior was studied in detail. It was found that the gel fiber exhibited a large swelling in an alkaline solution and contracting in an acid solution; the swelling change in length was above 90%; the responsive time of elongation/contraction was less than 20 s; the maximum contraction force was 20 N/cm2; and pH‐sensitivity was reversible. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Influence of organoclay and preparation technique on the morphology of polyamide6/polystyrene/organoclay nanocomposites
Authors: Yang Jintao , Sun Li , Xiang Saifei , He Jianlong , Gu Lianchao , Zhong Mingqiang 
Published: July 2008

AbstractTo have an improved insight about the compatibilization effect of organoclay on immiscible polymers, two different organoclays and preparation techniques were chosen to prepare polyamide6 (PA6)/polystyrene (PS)/organoclay ternary nanocomposites. The morphology analysis based on the results of X‐ray diffraction, transmission electron microscopy, and scanning electron microscopy demonstrated that the type of organoclay and preparation technique had a significant influence on the dispersion and distribution of organoclay in the polymer. It was concluded that blending PS/organoclay nanocomposite synthesized previously via in situ bulk polymerization, with PA6 can realize the full exfoliation of organoclay in the final ternarynanocomposite, while an intercalated structure was achieved by directly blending the three components. The distribution of organoclay could be controlled by tuning the surface property of clay, and hence the interfacial interaction between clay and the polymer matrix. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Effects of some solvents on the thermal and free‐volume properties of poly(4‐vinylpyridine) complexes
Authors: Mazroua A. , Gomaa E. 
Published: July 2008

AbstractModified poly(4‐vinylpyridine) (P4VP) and its complexes were prepared with different solvents such as benzene, toluene, and xylene as well as potassium chloride (KCl) and copper chloride (CuCl2). Fourier transform infrared spectroscopy, thermal analysis, and positron annihilation spectroscopy were used to investigate the properties of the modified P4VP and its complexes. It was concluded that complexes were formed between the polymer and solvents via quaternization of nitrogen in the ring with the solvents and also with KCl and CuCl2·2H2O. Furthermore, the modified P4VP–CuCl2 complexes were more stable than the modified P4VP–KCl complexes, and these complexes were more stable than the P4VP–solvent complexes. Ortho‐positronium components (τ3, I3) were used to estimate the nanoscale free‐volume hole size (Vf) and the free‐volume fraction (f %). The free‐volume hole size and its fractions depended on the addition of solvents and metals to the polymer. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Degradation and life prediction of a natural rubber engine mount compound
Authors: Ngolemasango Frederick E. , Bennett Martyn , Clarke Jane 
Published: July 2008

AbstractTo assess and predict the functional life of a natural rubber engine mount compound, the mechanical property changes were determined under accelerated aging conditions. The rubber was aged at temperatures ranging from 70 to 110°C for times ranging from 1 h to 5 weeks. Tensile and fatigue measurements were used to characterize the aging trends and mechanisms of the engine mount compound. With the time–temperature superposition approach, the activation energy was found to be about 98 kJ/mol for the elongation at break, 93 kJ/mol for the tensile strength, and 60 kJ/mol for the fatigue life. The tensile strength after aging for 13 weeks at 50°C was predicted to be 18.73 MPa, which was very close to the experimental value of 19.04 ± 2.25 MPa. With a 50% reduction in the tensile strength used as the failure criterion, it was predicted that the tensile strength of the engine mount compound would take 80 days to decrease by 50% at 70°C. At 23°C, it would last approximately 140 times (31 years) its lifetime at 70°C. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Synthesis and characterization of electrically conducting copolymers based on benzene and biphenyl
Authors: Simitzis Johannis , Triantou Despina , Soulis Spyridon 
Published: July 2008

AbstractPoly(p‐phenylene) (H‐PPP), which is one of the firstly investigated conducting polymer, has the disadvantage of difficult processability because it is infusible and insoluble. The use of biphenyl instead of benzene leads to ortho‐, meta‐, para‐polyphenylenes (H‐PP) which are more soluble and easier to be processed, however their electrical conductivity is lower. Copolymers of polyphenylenes (C1 and C2) and corresponding homopolymers (H‐PPP and H‐PP) were produced by the oxidative cationic polymerization of benzene and/or biphenyl. The soluble (‐S) and the insoluble (‐I) in chlorobenzene polyphenylenes were separated (H‐PP‐I, H‐PP‐S, C1‐I, C1‐S, C2‐I, and C2‐S) and they were doped with a solution of FeCl3. All polyphenylenes were studied by FTIR, XRD, TGA, and their electrical conductivity with constant current was determined. Pronounced differences between the copolymers and the homopolymers were observed, indicating the different structure of the former. The values of the electrical conductivity of doped insoluble copolymers (10−4 and 10−5 S/cm) are between that of H‐PPP (10−3 S/cm) and H‐PP‐I (10−6 S/cm). The values of the electrical conductivity of doped soluble copolymers (10−5 S/cm) are considerably higher than that of H‐PP‐S (10−9 S/cm). The new electrically conductive polyphenylenes that were produced differ significantly from the corresponding homopolymers and combine good electrical conductivity and solubility. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Preparation and cytocompatibility of chitosan‐modified polylactide
Authors: Xiao Yumei , Li Dongxiao , Chen Xuening , Lu Jian , Fan Hongsong , Zhang Xingdong 
Published: July 2008

AbstractChitosan‐modified PLA (CMPLA) was fabricated to improve cytocompatibility of polylactide (PLA). PMAA‐grafted PLA (PMAA‐PLA) was obtained through α‐methacrylic acid (MAA) grafted polymerization on PLA surface with photooxidization and UV irradiation. Steady PMAA‐PLA microparticle suspension with an average size as 172.8 ± 3.6 nm and zeta potential as −95.0 ± 0.6 mV was prepared through solvent volatilization. By static electricity interaction and other interactions between PMAA‐PLA microsparticles and chitosan molecules, CMPLA was obtained. FTIR, XPS, SEM, and zeta potential analyses indicated that CMPLA was modified with chitosan molecules uniformly. Compared with the PLA control, CMPLA adapted to supporting the attachment and proliferation of L929 cells better. The obtained CMPLA was expected to be used as perfect biomaterial for tissue regeneration. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Influence of fiber modification on interfacial adhesion and mechanical properties of pineapple leaf fiber‐epoxy composites
Authors: Lopattananon N. , Payae Y. , Seadan M. 
Published: July 2008

AbstractThree kinds of surface treatment, that is, the alkalization (5% w/v NaOH aqueous solution), the deposition of diglycidyl ether of bisphenol A (DGEBA) from toluene solution (1% w/v DGEBA), and the alkalization combined with the deposition of DGEBA (5% w/v NaOH/1% w/v DGEBA) were applied to modify interfacial bonding and to enhance mechanical properties of pineapple leaf fiber (PALF) reinforced epoxy composites. The fiber strength and strain were measured by single fiber test and the fiber strength variation was assessed using Weibull modulus. Furthermore, a fragmentation test was used to quantify the interfacial adhesion of PALF‐epoxy composite. It was verified that the interfacial shear strength of modified PALFs was substantially higher than that of untreated PALF by almost 2–2.7 times because of the greater interaction between the PALFs and epoxy resin matrix. The strongest interfacial adhesion was obtained from the fibers that had been received the alkalization combined with DGEBA deposition. Moreover, the flexural and impact properties of unidirectional PALF‐epoxy composites were greatly enhanced when reinforced with the modified PALFs due to an improvement in interfacial adhesion, particularly in the synergetic use of 5% NaOH and 5% NaOH/1% DGEBA. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Preparation of poly(styrene‐block‐acrylamide)/organic montmorillonite nanocomposites via reversible addition–fragmentation chain transfer
Authors: Qu Yuan‐Zhi , Su Yi‐Nao , Sun Jin‐Sheng , Wang Kui‐Cai 
Published: July 2008

AbstractUsing dithioester as a chain‐transfer agent and azobisisobutyronitrile as an initiator, we synthesized amphiphilic poly(styrene‐block‐acrylamide) [P(St‐b‐Am)] by the reversible addition–fragmentation chain transfer (RAFT) polymerization method. To improve the heat stability of the block polymers, amphiphilic P(St‐b‐Am)/organic montmorillonite (O‐MMT) nanocomposites were successfully prepared by the addition of O‐MMT during the preparation of the block polymer. The nanocomposites were tested by gel permeation chromatography, IR spectroscopy, X‐ray diffraction, transmission electron microscopy, and thermogravimetry. As for polystyrene (PSt)/O‐MMT, RAFT polymerization could control the molecular weight and the molecular weight distribution of PSt. PSt/O‐MMT was used as a macro RAFT agent to conduct the polymerization of acrylamide, and P(St‐b‐Am)/O‐MMT nanocomposites were prepared. Nanosize layers of montmorillonite were dispersed in the block polymer matrix, and exfoliative nanocomposites were formed. Therefore, the P(St‐b‐Am)/O‐MMT nanocomposites had a better heat stability than before. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Effects of a silane coupling agent on the exfoliation of organoclay layers in polyurethane/organoclay nanocomposite foams?
Authors: Han Mi Sun , Kim Youn Hee , Han Sung Jae , Choi Seok Jin , Kim Sang Bum , Kim Woo Nyon 
Published: July 2008

AbstractAn attempt was made to synthesize polyurethane (PU)/organoclay nanocomposite foams with high thermal insulation properties. The organoclay was modified by polymeric 4,4′‐diphenylmethane diisocyanate (PMDI) with a silane coupling agent. The structure of the organoclay‐modified PMDI with the silane coupling agent was determined by Fourier transform infrared spectroscopy and nuclear magnetic resonance. Transmission electron micrographs and wide‐angle X‐ray diffraction patterns showed that the interlayer distance increased for the PU/organoclay nanocomposites with the addition of the silane coupling agent. It was expected that the distance between the organoclay layers would increase and that the organoclay would be dispersed on a nanoscale in the PU matrix because of the organic/inorganic hybrid bond formation between the organoclay and silane coupling agent. Compressive and flexural strengths of the PU/silane coupling agent/organoclay nanocomposite foams were similar to those of the PU/organoclay nanocomposite foams. However, the thermal conductivity appreciably decreased from 0.0250 to 0.0230 W/m h °C in the PU/silane coupling agent/organoclay nanocomposite foams. Scanning electron micrographs showed that the cell size of the PU/silane coupling agent/clay nanocomposite foams also decreased. On the basis of these results, it is suggested that the smaller cell size and lower thermal conductivity of the PU/silane coupling agent/organoclay nanocomposite foams were mainly due to enhanced exfoliation of the organoclay layers by the silane coupling reaction. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Effects of styrene oligomers and polymers on the suspension polymerization behavior and properties of expandable polystyrene
Authors: Schellenberg Jürgen 
Published: July 2008

AbstractStyrene oligomers are formed by a free‐radical mechanism during the thermal polymerization of styrene in storage. The effects of these compounds on the preparation of expandable polystyrene (EPS) were investigated with respect to suspension polymerization behavior and the properties of the impregnated polystyrene beads produced. Styrene dimers and trimers up to concentrations of 0.2 wt % did not affect the stability of the suspension during the polymerization and impregnation stages. Besides differentiated effects on the particle size distributions of the polymers and on the polymerization rate, no chain‐transfer activity of the oligomers was observed, and this confirmed the assignment of chain transfer to the Diels–Alder dimer in the literature. The investigation of the foaming behavior of the pentane‐impregnated EPS beads indicated a significant reduction of the prefoaming density caused by styrene dimers and trimers. This behavior resulted from a decrease in the glass‐transition temperatures of these polymers. The effects of high‐molecular‐weight polystyrene, formed in addition to oligomers during storage by the thermal polymerization of styrene, on the polymerization behavior and polymer properties of EPS were also investigated. The results showed a significant impact on the suspension stability that was dependent on the concentration of the high‐molecular‐weight polystyrene. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008