bluuebunny/crossref_metadata_2025 huggingface dataset:
Sedimentary deposits of the 26 December 2004 tsunami on the northwest coast of Aceh, Indonesia
Authors: Moore Andrew , Nishimura Yuichi , Gelfenbaum Guy , Kamataki Takanobu , Triyono Rahmat
Published: August 2014

The 2004 Sumatra-Andaman tsunami flooded coastal northern Sumatra to a depth of over 20 m, deposited a discontinuous sheet of sand up to 80 cm thick, and left mud up to 5 km inland. In most places the sand sheet is normally graded, and in some it contains complex internal stratigraphy. Structures within the sand sheet may record the passage of up to 3 individual waves. We studied the 2004 tsunami deposits in detail along a flow-parallel transect about 400 m long, 16 km southwest of Banda Aceh. Near the shore along this transect, the deposit is thin or absent. Between 50 and 400 m inland it ranges in thickness from 5 to 20 cm. The main trend in thickness is a tendency to thicken by filling low spots, most dramatically at pre-existing stream channels. Deposition generally attended inundation—along the transect, the tsunami deposited sand to within about 40 m of the inundation limit. Although the tsunami deposit contains primarily material indistinguishable from material found on the beach one month after the event, it also contains grain sizes and compositions unavailable on the current beach. Along the transect we studied, these grains become increasingly dominant both landward and upward in the deposit; possibly some landward source of sediment was exposed and exploited by the passage of the waves. The deposit also contains the unabraded shells of subtidal marine organisms, suggesting that at least part of the deposit came from offshore. Grain sizes within the deposit tend to fine upward and landward, although individual units within the deposit appear massive, or show reverse grading. Sorting becomes better landward, although the most landward sites generally become poorly sorted from the inclusion of soil clasts. These sites commonly show interlayering of sandy units and soil clast units. Deposits from the 2004 tsunami in Sumatra demonstrate the complex nature of the deposits of large tsunamis. Unlike the deposits of smaller tsunamis, internal stratigraphy is complex, and will require some effort to understand. The Sumatra deposits also show the contribution of multiple sediment sources, each of which has its own composition and grain size. Such complexity may allow more accurate modeling of flow depth and flow velocity for paleotsunamis, if an understanding of how tsunami hydraulics affect sedimentation can be established.
Variation of choroidal thickness and vessel diameter in patients with posterior non-infectious uveitis
Authors: Bittencourt Millena G , Kherani Saleema , Ferraz Daniel A , Ansari Mehreen , Nasir Humzah , Sepah Yasir J , Hanout Mostafa , Do Diana V , Nguyen Quan Dong
Published: August 2014

Background

Choroidal thickness (CTh) and choroidal vessel diameter (VD) in the Haler’s layer were evaluated as markers of inflammatory insult in non-infectious uveitis (NIU). Spectral-domain optical coherence tomography (Spectralis®, Heidelberg Engineering Inc.) scans were acquired from 23 normal subjects (39 eyes – group 1), 7 subjects with high myopia (14 eyes – group 2), and 19 patients with NIU (23 eyes – group 3). In groups 1 and 2, CTh and VD were measured at 3 different points of the same horizontal OCT scan passing through the fovea and a mean calculated. Mean CTh and VD were calculated in 2 other locations, 2 mm superior and inferior from the chosen foveal horizontal scan. In group 3, three measurements of CTh and VD were obtained within 1 mm of a horizontal scan passing through a retinal lesion; mean CTh and VD were then computed. A ratio (R) between the VD and the corresponding CTh was calculated.

Results

Group 1, 2 and 3 mean age was 29.6, 29.1 and 45.9 years, respectively. Sixteen normal subjects, three myopic subjects and six NIU patients were male.. Group 1 mean CTh did not differ from group 2 (261.6±45.6 vs. 260.2±50.6 µm µm; p>0.05); mean VD was marginally higher in Group 2 (159.8±32.2 vs. 163.2±33.2 µm; p>0.05). Group 3 demonstrated thinner CTh (193.6±54.6 µm) than Groups 1 and 2 (p = 0.02 and <0.001). Group 3 mean VD (123.6±37.4 µm) was also less than that in Groups 1 and 2; the difference was statistically significant only when compared to group 2, p = 0.01. R did not differ across groups (p-values >0.05), indicating that variations in CTh and VD followed the same trend.

Conclusions

The study reports potential quantitative OCT-derived parameters that may be explored in future trials of non-infectious uveitis. Thinning of choroid and decrease of vessel diameter are observed in patients with chronic NIU compared to controls.
A Model of BMD Changes After Alendronate Discontinuation to Guide Postalendronate BMD Monitoring
Authors: McNabb Brian , Vittinghoff Eric , Eastell Richard , Schwartz Ann V. , Bauer Douglas C. , Ensrud Kristine , Barrett-Connor Elizabeth , Black Dennis M.
Published: August 2014

Context:

Women stopping alendronate are commonly monitored with serial bone mineral density (BMD) measurements, yet no information exists on how frequently or for whom these measurements should be performed.

Objective:

The objective of the study was to develop a tool to guide post-alendronate BMD monitoring.

Design:

A predictive model was constructed to estimate the time until a given percentage of women's BMD T-scores drop below a given threshold that indicates a management change (such as retreatment) would be considered. This model was then used to estimate the time it would take for groups of women defined by their baseline BMDs to drop below the given threshold.

Setting:

Data were derived from the Fracture Intervention Trial Long Term Extension (FLEX), the largest multicenter clinical trial of its type to date.

Participants:

Four hundred four women who had received an average of 5.1 years of alendronate during the Fracture Intervention Trial and were subsequently observed for 5 treatment-free years (on placebo) during the FLEX trial were used to estimate the change in BMD over time.

Results:

If a management change such as alendronate reinitiation would be considered when BMD T-score drops below −2.5, the model shows that women with total hip BMD greater than −1.9 T-scores at the time of alendronate discontinuation have less than a 20% probability that at follow-up, monitoring BMD will be below the threshold within 5 years. The model performed similarly, and results are provided over a range of management change thresholds from −1.75 to −3 T-scores.

Conclusions:

Using the tool developed in this analysis, it is possible to estimate when BMD repeat measurement after alendronate discontinuation could potentially be useful. Measuring BMD within 5 years after alendronate discontinuation is unlikely to change management for women with total hip BMD 0.6 T-scores above a prespecified retreatment threshold within the range of −1.75 to −3 T-scores.
Serum Adipocyte Fatty Acid Binding Protein Levels Are Positively Associated With Subclinical Atherosclerosis in Chinese Pre- and Postmenopausal Women With Normal Glucose Tolerance
Authors: Hao Yaping , Ma Xiaojing , Luo Yuqi , Shen Yun , Dou Jianxin , Pan Xiaoping , Bao Yuqian , Jia Weiping
Published: August 2014

Context:

Recent studies highlight a critical interaction between adipocyte fatty acid binding protein (A-FABP) and cardiovascular disorders. However, associations of A-FABP with subclinical atherosclerosis in a population with normal glucose tolerance remain unknown.

Objective:

The study aimed to evaluate the relationship between A-FABP and carotid intima-media thickness (C-IMT) in a Chinese population with normal glucose tolerance.

Design and Setting:

A cross-sectional analysis was conducted of 2253 cardiovascular disease-free normal glucose tolerance subjects (835 men, 1418 women; 20–78 years old) from the Shanghai Obesity Study.

Main Outcome and Measures:

C-IMT was measured by B-mode ultrasound and used to assess subclinical atherosclerosis. Serum A-FABP levels were quantified by a sandwich ELISA.

Results:

The median serum level for A-FABP was 4.0 ng/mL (interquartile range: 2.6–6.0 ng/mL), and significantly higher in women than men (P < .001). After adjusting for age and body mass index (BMI), a partial correlation analysis showed that A-FABP levels correlated with C-IMT in men, premenopausal, and postmenopausal women (P = .024, .006, and .016, respectively). Furthermore, C-IMT increased along with quartile A-FABP values (all P for trend <.001). Regression analyses demonstrated that A-FABP was associated with C-IMT only in women (P = .044 and .001 for pre- and postmenopausal, respectively). Moreover, A-FABP was identified as a risk factor for C-IMT in pre- and postmenopausal women with a normal BMI (P < .001 and P = .012, respectively).

Conclusions:

Serum A-FABP levels independently and positively correlate with subclinical atherosclerosis in pre- and postmenopausal Chinese women with normal glucose tolerance after adjustments for the traditional risk factors.
A cluster of methylations in the domain IV of 25S rRNA is required for ribosome stability
Authors: Gigova Andriana , Duggimpudi Sujitha , Pollex Tim , Schaefer Matthias , Koš Martin
Published: August 2014

In all three domains of life ribosomal RNAs are extensively modified at functionally important sites of the ribosome. These modifications are believed to fine-tune the ribosome structure for optimal translation. However, the precise mechanistic effect of modifications on ribosome function remains largely unknown. Here we show that a cluster of methylated nucleotides in domain IV of 25S rRNA is critical for integrity of the large ribosomal subunit. We identified the elusive cytosine-5 methyltransferase for C2278 in yeast as Rcm1 and found that a combined loss of cytosine-5 methylation at C2278 and ribose methylation at G2288 caused dramatic ribosome instability, resulting in loss of 60S ribosomal subunits. Structural and biochemical analyses revealed that this instability was caused by changes in the structure of 25S rRNA and a consequent loss of multiple ribosomal proteins from the large ribosomal subunit. Our data demonstrate that individual RNA modifications can strongly affect structure of large ribonucleoprotein complexes.
Was ist, was muss, was soll? – Die Universitätsbibliothek Gießen ließ fragen und bekam Antworten
Authors: Martin-Konle Claudia
Published: August 2014

Erfahrungen und Erwartungen zu eruieren, um Mittel bedarfsorientiert einzusetzen bzw. einzuwerben – so war die Motivation der Universitätsbibliothek Gießen, eine repräsentative Umfrage unter ihrer Kundschaft durchzuführen. Neutralität, neben Professionalität des Erhebungsinstruments und der Auswertung, garantierte die Professur für Empirische Bildungsforschung der Justus-Liebig-Universität, die die Studie im November 2013 durchführte. 5.911 Fragebögen wurden ausgewertet und umgehend für die inneruniversitäre Diskussion um Sondermittel herangezogen, mittelfristig werden sie für bauliche Planungen von Bedeutung sein: Print-Lehrbücher und Gruppenarbeitsräume stehen auf der studentischen Wunschliste ganz oben.
Improvement of catalytic activity and comonomer response in ethylene/norbornene copolymerization initiated with ansa-metallocene
Authors: Lee Dong-ho , Choi Yi Yeong , Lee Jo Hoon , Park Yoon Seok , Woo Sang Sun
Published: August 2014

The copolymerization of ethylene (E) and norbornene (N) was carried out with ansa-metallocenes such as rac-Et(Ind)2ZrCl2 (1) and iPr(CpFlu)2ZrCl2 (2) cocatalyzed by modified methylaluminoxane in the presence of a 3rd monomer. As 3rd monomers, not only ɑ-olefins but also vinyl monomers were used. With the addition of a small amount of 3rd monomer, the catalyst activity of 1 and 2 could increase depending on the structure and amount of 3rd monomer added. The glass transition temperature (Tg) of polymer obtained in the presence of a 3rd monomer was higher than that of E/N copolymer. By using an appropriate mixed medium, the catalyst activity and Tg of the polymer could be adjusted. With 13C NMR analysis, it was found that the incorporation of N in the polymer was enhanced by the addition of 3rd monomer. The 3rd monomer effect was also observed for the copolymerization system of E and 5-ethylidene-2-norbornene.
Long period analysis in blends of high-density and lowdensity polyethylene
Authors: Cheikh Larbi Fadhel Ben , Halary Jean Louis
Published: August 2014

Long period calculations from small angle X-ray scattering experiments (SAXS) is a well-known way to describe biphasic polymeric systems. In the case of semi-crystalline homopolymers, more and more sophisticated models have been proposed to account for the SAXS intensity profiles. However, they use too many parameters to be applied to systems including two crystalline phases and an amorphous phase. Therefore, we propose a crude alternative, based on a generalization of the old paracrystalline Hoseman model, in order to consider the case of blends of high-density (HDPE) and low-density (LDPE) polyethylene. The crystalline lamella thickness distribution function is taken as the sum of two Gaussians (bimodal function 2G). As far as the amorphous domain thickness distribution function is concerned, either an exponential distribution (E) or a Gaussian distribution (G) is used. The model 2G/G proves to be much more realistic than the model 2G/E, with respect to the long period evolution as a function of HDPE/LDPE blend composition.
Syntheses and solution properties of water-soluble poly(p-phenylene)s bearing oligo(ethylene oxide) and trialkylamino side groups
Authors: Traser Steffen , Wittmeyer Patrick , Rehahn Matthias
Published: August 2014

Pd-catalyzed Suzuki coupling is used to prepare poly(p-phenylene)s (PPPs) bearing oligo(ethylene oxide)s (OEOs) and trialkylamino groups as lateral substituents. The OEO substituents require very specific reaction conditions during monomer synthesis - presumably due to their coordinating oxygen atoms - but do not affect the subsequent Pd-catalyzed polycondensation process. In contrast to this, the lateral amino groups lower the degree of polycondensation of the PPPs considerably when their nitrogen atom is placed in the β-position of the side chains. When there is a longer spacer group between the amino nitrogen and the aromatic ring to be coupled, however, high-molecular-weight PPPs can be obtained. Provided an appropriate substitution pattern and long OEO side chains are used, the resulting PPPs are readily soluble not only in organic solvents but even in aqueous media. For one of these PPPs, the degree of protonation has been determined as a function of pH, using 1H and 13C NMR spectroscopy as well as potentiometry. It is shown that the polymer is completely deprotonated at pH > 10.5 and quantitatively protonated at pH < 4.0.
Enzymatic polymerization of m-substituted phenols in the presence of 2,6-di-O-methyl-β-cyclodextrin in water
Authors: Tonami Hiroyuki , Uyama Hiroshi , Kobayashi Shiro , Reihmann Matthias , Ritter Helmut
Published: August 2014

Enzymatic polymerization of m-substituted phenols has been achieved in the presence of 2,6-di-O-methyl-β-cyclodextrin (DM-β-CD) in a buffer. A watersoluble complex of the monomer and DM-β-CD was formed and polymerization was performed by peroxidase catalyst to give the polymer in high yields. Formation of the inclusion complex was confirmed by NOESY NMR. The association constant was determined by NMR and found to depend on the monomer structure.
‘Living’ cationic copolymerization of isobutyl vinyl ether with methyl vinyl ether: copolymerization parameters and properties of the copolymers
Authors: Confortini Ondine , Verdonck Beatrice , Goethals Eric J.
Published: August 2014

The copolymerization of isobutyl vinyl ether (IBVE) with methyl vinyl ether (MVE), initiated by the system 1,1-diethoxyethane/trimethylsilyl iodide/zinc iodide and conducted at 0°C in toluene, was found to be ‘living’ just as the homopolymerizations of these monomers. Monomer reactivity ratios are rIBVE = 1.08 and rMVE = 0.43. The lower critical solution temperature of polyMVE in water, situated around 37°C, was lowered to 10°C (for a 0.25 wt.-% solution) when 6 mol-% of IBVE units were introduced in copolymers of molar mass 3000 - 7000 g/mol. At higher IBVE contents, the polymers are insoluble in water at all temperatures.
Comparison of structure formation upon drawing of gel-cast and melt-crystallised UHMWPE films
Authors: Ivan’kova Elena , Vasilieva Valeria , Myasnikova Liuba , Marikhin Vyacheslav , Henning Sven , Michler Goerg H.
Published: August 2014

Structure and mechanical properties of ultra-high molecular weight polyethylene (UHMWPE) films of different draw ratios produced from gel-cast and meltcrystallised samples by multi-stage zone drawing have been studied in order to investigate the structural development and to clarify the role of interfaces between morphological units in the mechanical behaviour. The complex hierarchy of fibrillar structures generating upon neck formation is revealed. It is shown that the rearrangement of initial chain-folded crystallites into a microfibrillar structure occurs inside the volumes of supermolecular structures of larger sizes (spherulites in the melt-crystallised films and stacks of lamellae in the gel-crystallised films), the boundaries between the latter not having disappeared. Both the initial spherulites and stacks of lamellae with internally rearranged microfibrillar structure elongate upon drawing and comprise spindle-like units - macrofibrils - which are well resolved in scanning electron microscopy. Moreover, superfibrils have been revealed in the melt-crystallised films for the first time. They are, as suggested, the remnants of deformed and rearranged nascent polymer particles. Thus, the volume of the drawn films is considered to be full of interfaces. It is suggested that the majority of conformational defects, like chain ends, loops, tie molecules, entanglements, etc., are expelled from fibrillar crystallites in both intra- and interfibrillar regions. In addition to that, the interfibrillar spaces are crossed by tie molecules and micro- and macrofibrils. All of them hinder interfibrillar slip. The differences in creep and recovery of the investigated films are discussed in terms of density of packing and degree of connectivity of various scale fibrillar structural units. The lateral boundaries and the tips of fibrils are considered to be the weakest structural sites from which kink band formation and subsequent fracture of the loaded material begin.
Effect of long chain branching on linear-viscoelastic melt properties of polyolefins
Authors: Vega Juanfran , Aguilar Marina , Peón Jon , Pastor David , Martínez-Salazar Javier
Published: August 2014

The aim of this review is to provide evidence that rheological testing is a potent tool for characterising polymers in the melt. An effort has been made in order to gather results in conventional and model polyolefins, and correlating them with phenomena occurring at the molecular level. We have focused our interest on long chain branching (LCB). In the case of materials containing long side-chain branches, strong effects on viscosity, elastic character and activation energy of flow are general features. Literature results mostly indicate that the effect of polydispersity on these parameters could be very similar to that expected due to the presence of LCB - notwithstanding that the effects of LCB seem to be stronger than those due to polydispersity for a given molecular weight. Different relaxation processes appear as a consequence of the presence of LCB: slower terminal relaxation behaviour than of linear counterparts, and faster additional branch relaxation at higher frequencies, clearly distinguishable from polydispersity effects. To measure the amount of LCB from limited viscoelastic data and molecular properties seems to be a suitable instrument to explain the rheological features of the different polymers, but it fails when the results are compared with measured values of LCB density in model polymers. The actual framework leads us to say that the number of branches is less important than the topology itself. Therefore, the position and architecture of the branches along the polymer main chain are the main factors that control the rheology of the material.
Poly(phenylene sulfide) – some news on an old polymerization
Authors: Haubs Michael , Wagener Reinhard
Published: August 2014

High performance thermoplastic poly(p-phenylene sulfide) (PPS) is commercially produced from sodium sulfide and p-dichlorobenzene:

Na-S-Na + Cl-(C6H4)-Cl → -[C6H4S]- + 2 NaCl

At a first glance, this looks like a classical step growth polymerization of the A-A + B-B type. There has been considerable discussion and scientific investigation about the reaction mechanism. Today, it is accepted that PPS polymerization is a step growth polymerization with chain length dependent end group reactivities. This paper suggests to add a polymer chain cleavage reaction to the known kinetic model in order to improve the fit of experimental observation and modeling results. Implications of this reaction kinetic model for the design and engineering of an optimized PPS polymerization process are discussed.
Poly-L-lactide nanofibers by electrospinning – Influence of solution viscosity and electrical conductivity on fiber diameter and fiber morphology
Authors: Zeng Jun , Haoqing Hou , Schaper Andreas , Wendorff Joachim H. , Greiner Andreas
Published: August 2014

Poly-L-lactide (PLA) fibers were obtained by electrospinning of PLA / dichloromethane solutions. Formation of beaded fibers combined with decreased fiber diameters were observed for low PLA concentrations in solution. Increase of the electrical conductivity by addition of pyridinium formiate (PF) caused a significant reduction of bead formation. The electrospinning of dilute PLA / PF / dichloromethane solutions resulted in PLA nanofibers. Systematic variations clearly identified the solution viscosity and the electrical conductivity at otherwise fixed parameters (surface tension, molecular weight, electrode geometry, electrical field, etc.) as crucial parameters for the formation of beads upon electrospinning of PLA / dichloromethane solutions.
Comprehensive fire behaviour assessment of polymeric materials based on cone calorimeter investigations
Authors: Schartel Bernhard , Braun Ulrike
Published: August 2014

Bench scale performance based cone calorimeter investigations were conducted on glass fibre reinforced polyamide 66 (PA-66) and high impact polystyrene (HIPS) materials. Red phosphorus and magnesium hydroxide were used as fire retardants. Dilution, heat sink, barrier and charring mechanisms are considered to be active in the condensed phase. Dilution, cooling and flame poisoning mechanisms are discussed for the gas phase. Cone calorimeter data are used to give a comprehensive fire behaviour assessment in terms of the propensity to cause a quick growing fire and of the propensity to cause a fire of long duration. The external heat flux is varied between 30 and 75 kW/m2 so that the results for combustion behaviour and flame retardancy, respectively, are valid for different fire scenarios and fire tests. Results on the intrinsic contribution of the steady heat release rate per unit area reveal information about the flammability behaviour. UL 94 results are predicted in close correspondence to UL 94 experiments.
Effect of composition on the properties of PMMAPTEGDMA shrinkage-controlled copolymers
Authors: Velázquez Rodrigo , Reyes Julio , Castaño Victor M.
Published: August 2014

Acrylic copolymers made of a casting syrup (prepared from poly(methyl methacrylate) (PMMA) dissolved in methyl methacrylate) and triethylene glycol dimethacrylate (TEGDMA) were synthesized by promoting the decomposition of benzoyl peroxide (BP) with dimethyl-p-toluidine. In addition, conventional copolymers, made of methyl methacrylate and triethylene glycol dimethacrylate monomers, were synthesized via thermal decomposition of BP. The two types of reaction were carried out as bulk polymerizations. Both types of copolymers were studied applying scanning electron microscopy, IR and micro-Raman spectroscopy, differential scanning calorimetry, and dilatometry. It was found that the conventional polymer is a MMA-TEGDMA copolymer without phase separation, while the phase-separated polymer contains microdomains. The shrinkage of the polymers, as well as their morphology, can be easily controlled through the chemical composition.
Novel polyelectrolyte complex between chitosan and poly(2-acryloylamido-2-methylpropanesulfonic acid-coacrylic acid)
Authors: Paneva Dilyana , Stoilova Olya , Manolova Nevena , Rashkov Iliya
Published: August 2014

A novel polyelectrolyte complex between chitosan and copolymers of 2- acryloylamido-2-methylpropanesulfonic acid (AMPS) and acrylic acid (AA) has been prepared. The formation of the complex has been studied viscometrically, gravimetrically and turbidimetrically in the pH range from 1.2 to 5.8. The stoichiometry and the yield of the complex depend on the copolymer composition and on the pH value of the medium. In the case of copolymers with low content of AMPS units the complexes are enriched in copolymer when formed in the pH range from 1.2 to 4.8. In this pH region mainly AMPS units take part in complex formation. A stoichiometric complex forms only at higher pH values due to the increased number of complexable carboxylate ions of AA units. The stoichiometry of the complexes prepared from copolymers with higher content of AMPS units is close to equimolar and is less sensitive to pH. The obtained complexes are stable up to pH 8. It has been shown that chitosan once included in the complexes remains degradable under the action of a crude enzyme complex produced by the soil fungus Trichoderma viride. The rate of the enzymatic hydrolysis decreases in the order chitosan/PAA > chitosan/P(AMPS-co-AA) > chitosan/PAMPS. Tests on the proliferation of T. viride embedded in chitosan beads have shown that coating the beads with chitosan/P(AMPS-co-AA) complex does not hamper the development of the microorganisms.
Structure and dielectric properties of polymeric composites with ferroelectric fillers
Authors: Tchmyreva Viktoria V. , Ponomarenko Anatoliy T. , Shevchenko Vitaliy G.
Published: August 2014

Dielectric properties of composite materials, polymer - ferroelectric filler, were investigated in wide frequency and temperature ranges. It has been shown that dielectric properties of polymer composites are a function of the size and concentration of ferroelectric filler particles, since these particles contain a defective outer surface layer with dielectric properties significantly different from those of the ferroelectric bulk. Dielectric properties of composites were found to depend on the type and properties of the polymer matrix, as well as on the method and conditions of composite preparation. Composites cured in the measurement cell possess a more porous structure, their dielectric constant ε' being lower compared to compression molded samples. ε' of polypropylene composites in the ferroelectric phase is higher than that of epoxy resin composites.
On the key role of the interface in the cationic polymerisation of p-methoxystyrene in miniemulsion
Authors: Cauvin Séverine , Dos Santos Rosalina , Ganachaud François
Published: August 2014

This paper presents the latest improvements, in terms of reactivity and molar masses, of the process of cationic polymerisation of p-methoxystyrene in miniemulsion, which was published previously [Cauvin et al., Macromolecules 2002, 35, 7919]. The formulation was adapted to change dramatically the specific surface and the polarity of the interface where the polymerisation takes place. Adding hexadecane permits to significantly decrease the particle diameter and thus to favour a faster polymerisation rate. In addition, droplets generated by sonication are ideally covered by the INISURF (initiator/surfactant) dodecylbenzenesulfonic acid and nucleate quantitatively (true miniemulsion polymerisation). Hexadecane addition finally ensures a better stability of the polymerised dispersion. A more hydrophobic acidic surfactant, though used at much smaller concentrations, again allowed increasing the polymerisation rate. Both systems, however, show no improvements in terms of molar masses compared to those observed previously. By separating the initiating agent (a super acid such as triflic acid) from the surfactant (a non-ionic one) an increase of molar masses is obtained but accompanied by an important drop of the polymerisation rate.
Copolymers of 2-acryloylamido-2-methylpropanesulfonic acid and acrylic acid with anticoagulant activity
Authors: Paneva Dilyana , Stoilova Olya , Manolova Nevena , Danchev Dobri , Lazarov Zdravko , Rashkov Iliya
Published: August 2014

Copolymers of 2-acryloylamido-2-methylpropanesulfonic acid (AMPS) and acrylic acid (AA), as well as the corresponding homopolymers PAMPS and PAA, were studied in vitro on human pool plasma for their anticoagulant activity. The values of the haemostatic parameters - prothrombin time, activated partial thromboplastin time and thrombin time - depend on the composition and the concentration of the (co)polymers. Reptilase time remains unchanged on adding the (co)polymers. A broad concentration range from 16 μg/ml to 3 mg/ml was studied. The copolymers possess anticoagulant activity, which is higher at higher content of AMPS units. It was found that, at certain concentrations, the haemostatic parameters of PAMPS are close to that of heparin. PAA has the lowest anticoagulant activity.
Controlled grafting of poly(styrene-ran-n-butyl methacrylate) to isotactic polypropylene with nitroxidemediated polymerization
Authors: Sugino Yusuke , Yamamoto Katsuhiro , Miwa Youhei , Sakaguchi Masato , Shimada Shigetaka
Published: August 2014

A nitroxide (2,2,6,6-tetramethylpiperidin-1-oxyl, TEMPO) mediated polymerization method was applied to the graft polymerization of styrene (ST)/ n-butyl methacrylate (BMA) to isotactic polypropylene (PP). PP peroxides produced by γ-irradiation in air were used as macroinitiator for grafting. The molecular characteristics of grafted and free poly(ST-r-BMA) chains were analysed by gel permeation chromatography, NMR and IR measurements. The molecular weight of grafted poly(ST-r-BMA) cleaved from PP was slightly higher than that of free poly(ST-r-BMA) generated simultaneously in the reaction system. Polydispersities of these polymers were narrow, indicating that grafting proceeded in a living fashion. The incorporated amount of BMA into grafted poly(ST-r-BMA) was smaller than that of free poly(ST-r-BMA). It is considered that the local concentration of BMA around propagating ends of graft poly(ST-r-BMA) was lower than that around free poly(ST-r-BMA) because PP cannot be dissolved in BMA monomer but in ST monomer at the polymerization temperature.
Permeability of multi-layer structures
Authors: Solovyov Stanislav E. , Goldman Anatoliy Ya.
Published: August 2014

In this paper we show that ‘permeability’ of a heterogeneous structure with mass transport and thermodynamic properties varying across its thickness is a misleading concept leading to incorrect results and design decisions while two structural transmission rate equations are recommended for practical applications. The notion of structural identity of multi-layer films is introduced to explain the apparent failure of the ‘permeability’ concept. Structural identity of two or more films means the same material sequence in the structure relative to separated environments with constant relative thickness of each corresponding layer. Structurally identical films indeed have the same ‘permeability’, however the notion of identity is shown to contradict the practical goals of multi-layer film design. Engineering examples are provided to demonstrate potential misuses of the ‘permeability’ concept in practical multi-layer design decisions. Correct problem statements and calculation procedures are included. Some general limitations of transmission rate equations are also discussed. These include the role of boundary conditions, temperature and concentration dependence of permeant diffusivity and solubility in a polymer matrix, the presence of co-permeants, surface sorption effects, film thickness, homogeneity of polymer matrix for permeation purposes and correct utilization of available data for predicting gas transport properties of multilayer films.
Effect of styrene/ethylene/butylene/styrene block copolymer on the dynamic mechanical behaviour and processability of high-impact polystyrene
Authors: Rek Vesna , Holjevac Grgurić Tamara , Jelčić Želimir , Hace Drago
Published: August 2014

Blends of high-impact polystyrene (PS-HI) and styrene/ethylene/butylene/ styrene block copolymer (SEBS) were investigated to determine the effects of rubber on the polymer properties. The processing behaviour of the PS-HI + SEBS blends was analyzed and the dynamic mechanical behaviour of the processed blends was examined. The rheological behaviour of the prepared blends during processing was followed by measuring the torque, output and melt pressure in a twin extruder. Dynamical mechanical analysis was performed in the temperature range of -150 to 160°C. The blends were also investigated in the creep fatigue regime and relaxations were determined at 25 - 65°C. Master curves for the reference temperature 25°C were created using the time-temperature superposition principle. With increasing SEBS content there was not significant increase of the torque value for blends below a rubber content of 70 wt.-% with respect to neat PSHI. An influence of SEBS content on the increase of the apparent viscosity was observed above 40 wt.-% of SEBS. The curves of storage modulus E’, loss modulus E’’ and loss tangent tan δ vs. temperature are affected by lowering the hard phase (PS) content: tan δ of the soft phase ethylene/butylene (EB) increases, while tan δ for the hard phase and storage modulus decrease. All samples exhibit a single glass transition of the hard phase. At constant load the creep of PS-HI, SEBS and PS-HI + SEBS blends increases and the creep modulus decreases over a period of time for all samples examined. These effects are more pronounced in samples with lower hard phase content. The energy-time-temperature correspondence principle was applied to create master curves for the reference temperature 25°C for the creep modulus of PS-HI, SEBS and PS-HI + SEBS blends. Microscopic morphology results confirm the main conclusions obtained from the processing and dynamic mechanical behaviour of the blends. The phase-separated microstructure is more pronounced in PS-HI + SEBS blends. The rise in fracture energy with SEBS introduction appears in the whiteness of the SEM microphotographs, first as white crests, and in PS-HI + SEBS blends with higher SEBS content as globular structures.
Rheological behaviour of urea-formaldehyde adhesive resins
Authors: Christjanson Peep , Suurpere Aime , Siimer Kadri
Published: August 2014

An attempt is made to describe the complicated rheokinetic behaviour of urea-formaldehyde resins during storage, in close connection with the changes in their chemical structure. The alkali-promoted non-linear polycondensation during resin storage is evaluated by pre-gel viscosity measurements. Viscosity changes are described by a power law function using extrapolation to zero shear and infinitely high shear rates. During most of the period of viscosity increase, the rheological behaviour of studied resins is similar. The deviation from the power law dependence occurring in the initial low-rate growth of viscosity takes place because of formaldehyde redistribution, which does not lead to covalent network build-up. In the presence of methanol this period is extended due to the formation of stable methoxymethylene groups.
Metastable state of amphiphilic polysaccharide solutions
Authors: Simon Sébastien , Mocanu Georgeta , Picton Luc , Le Cerf Didier , Muller Guy
Published: August 2014

This communication reports the time-dependent viscometric behaviour of amphiphilic pullulan (with varied amount of grafted octyl groups, C8) solutions as a function of age and temperature. For lower C8 amount, no ageing effects were observed. With high amount of octyl-bearing groups, the solution exhibits a strong increase of viscosity caused by an increase of intermolecular associations and the simultaneous decrease of intramolecular associations. After longer time, a collapse of chains has been observed. This behaviour is favoured with concentration and temperature. These results evidence the metastable character of amphiphilic polymers in aqueous solution.
Comparative dielectric studies of segmental mobility in novel polyurethanes
Authors: Roussos Michalis , Konstantopoulou Anna , Kalogeras Ioannis M. , Kanapitsas Athanassios , Pissis Polycarpos , Savelyev Yuri , Vassilikou-Dova Aglaia
Published: August 2014

Molecular dynamics in selected novel linear/low-branched polyurethanes (PUs), based on oligo(oxytetramethylene glycol), 4,4'-diphenylmethanediisocyanate (MDI) or 2,6-toluenediisocyanate (TDI), and unsymmetrical dimethylhydrazine (I) and a derivative of that (II) as chain extenders (CE), were studied by dielectric techniques. Special attention was paid to the investigation of the α relaxation, associated to the glass transition, by dielectric relaxation spectroscopy (DRS) and thermally stimulated depolarization currents (TSDC). The TSDC method was used to study the interfacial Maxwell-Wagner-Sillars (MWS) relaxation, related to the accumulation of charges at the interfaces between soft-segment and hardsegment microdomains. The results obtained by DRS and TSDC were in good agreement with each other and in reasonable agreement with results for the microphase separation (MS) obtained by small-angle X-ray scattering and differential scanning calorimetry. TSDC proved to be an attractive complementary technique to DRS for the study of MS in PUs. The results suggest that the position of the MWS band, as well as its separation from the α band, is a good measure of the degree of MS. As regards the PUs studied here, the degree of MS enhances by increasing the mole ratio of CE, and by replacing MDI by TDI or CE I by CE II.
Effects of a pulsatile magnetic field on the atom transfer radical polymerization of 2-hydroxyethyl methacrylate in methanol
Authors: Iliev Stefko B. , Georgiev George S.
Published: August 2014

A more than twofold increase in the rate of 2-hydroxyethyl methacrylate atom transfer radical polymerization in methanol at 20°C was observed under the action of a pulsatile magnetic field. At the same time, the average molecular weight of the produced polymers decreased while the polydispersity increased slightly. The results are explained by assuming a shift of the equilibrium from the dormant species to the active propagating radicals under the action of the magnetic field.
Gel formation in frontal polymerization of 2-hydroxyethyl methacrylate
Authors: Pujari Narahari S. , Vishwakarma Avinash R. , Vishwakarma Avinash R. , Kelkar Mayuresh K. , Ponrathnam Surendra
Published: August 2014

Frontal polymerization of 2-hydroxyethyl methacrylate was investigated to study the effect of type and concentration of initiator, solvent and diluent on the existence of a front, on front velocity as well as front temperature. A significant effect of the type of initiator and its concentration was recorded. Poly(2-hydroxyethyl methacrylate) (PHEMA) was obtained predominantly as a gel. The different gels were evaluated for water and cyclohexane gain and porosity, and the mechanism of gel formation is discussed. Amongst the three diluents used (silica gel, β- cyclodextrin and silica sol), gel formation was highest in the presence of silica sol (≈ 42%). Pore dimensions were less than 15 nm and pore size distribution was narrow. PHEMA networks showed significantly higher water regain due to swelling than attributed to the pore volume as estimated by mercury porosimetry or cyclohexane regain. Kinetics of the equilibrium swelling ratio was studied.
Polymerization of styrene using 1,1,2,2-tetraphenyl-1,2- ethanediol as initiator in the presence of 2,2,6,6-tetramethyl- 1-piperidinyloxy
Authors: Wang Gang , Zhu Xiulin , Hu Dijun , Cheng Zhengping , Zhu Jian
Published: August 2014

The bulk polymerization of styrene using 1,1,2,2-tetraphenyl-1,2-ethanediol as initiator in the presence of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) was investigated. The results show that polymerization proceeded in a controlled/ ’living’ way, i.e., polymerization rate is first order with respect to monomer concentration. Molecular weights increase linearly with conversion and molecular weight distributions are relatively low (Mw/Mn = 1.10 - 1.35). Well-defined polystyrenes with α-hydrogen and TEMPO end groups were obtained.
Deformation of the lamellar structure in semi-crystalline polymers studied by computer simulations
Authors: Viana Júlio C. , Ribeiro Carlos J. , Dias Gustavo R.
Published: August 2014

Yield in a semi-crystalline polymer involves the disruption of the crystalline phase in an irreversible deformation process. In a semi-crystalline polymer, the crystalline lamellar regions are bridged together by inter-lamellar amorphous layers, which act as a loading transfer medium. The deformation of both phases is, therefore, to some extent inter-related. In this work we adopted a continuous mechanic approach (neglecting atomic/molecular interactions) of the lamellar deformation of semi-crystalline polymers in the sense that we simulated the mechanical response of a lamellar structure (two lamellae interconnected by amorphous regions) in a finite element analysis. The use of computer simulations allows studying independently the effect of each relevant morphological parameter on the mechanical response. Several simulations were performed considering isolated variations of the following morphological parameters: i) mechanical behaviour of the amorphous material; ii) thickness of the crystalline regions; iii) length of the amorphous regions; iv) number of amorphous regions connected with a crystalline lamella; v) relative angle between the crystalline and the amorphous regions; vi) mode of loading (tension and compression). The thickness of the crystalline lamellae is evidenced as the most significant factor affecting the tensile response of the lamellar structure, followed by the mechanical behaviour of the amorphous phase. The connection angle between amorphous and crystalline regions and the number of amorphous regions bridging adjacent crystalline lamellae play only a minor role. The length of the amorphous regions has a negligible influence. As expected, the lamellar structure shows also distinct behaviours under distinct loading modes, tensile loading showing the highest stresses.
Synthesis and electrooptical characterization of polysiloxanes containing indolyl groups acting as photoconductive substrates for photorefractive materials
Authors: Angelone Rocco , Castè Claudia , Castelvetro Valter , Ciardelli Francesco , Colligiani Arturo , Greco Francesco , Mazzotta Alessandro , Ruggeri Giacomo
Published: August 2014

Synthesis and electrooptical analysis of polysiloxane and poly-N-vinyl derivatives containing indolyl groups are reported. The indole group and some of its methyl derivatives have been taken into account in order to evaluate their behaviour, with respect to that of the widely employed carbazole group, when used as photoconductive centres attached to a polymer chain. The obtained data show that photoconductivity and traps formation mechanism can be inferred as functions of the physico-chemical parameters (electric dipole moment and ionization potential) of the different groups and polymers involved. To this end such parameters have been carefully computed for a series of pyrrole, indole and carbazole derivatives. The 2,3-dimethylindole derivative appears to be particularly promising due to its electrooptical behaviour in the red absorption region where measurements have been accomplished and are shown to be consistent with the theoretical predictions.
Interfacial studies of carbon fibre / polycarbonate composites using dynamic mechanical analysis
Authors: Paiva Maria C. , Mano João F.
Published: August 2014

Unidirectional composite material samples with ultrahigh modulus carbon fibres, treated and untreated by oxygen plasma, and a polycarbonate matrix were prepared and tested. Dynamic mechanical analysis (DMA) was used to study interfacial fibre/matrix interaction and the fragmentation test method was applied to determine interfacial shear strength. For the composite samples with treated carbon fibres, analyzed by DMA, a consistent shift of the loss modulus peak toward higher temperature was observed. The damping ratio was highly affected by residual stresses along the carbon fibre direction due to the large difference of thermal expansion coefficients of matrix and fibres. Critical fibre length and interfacial shear strength, obtained from the fragmentation test, showed substantial improvement for treated fibres as compared to the untreated ones. Plasma oxidation of the fibre surface improved considerably the fibre-matrix interaction. Care must be taken interpreting the DMA results, due to specific characteristics of the system studied.
Scratch velocity and wear resistance
Authors: Bermúdez M. Dolores , Brostow Witold , Carrión-Vilches Francisco J. , Cervantes Juan J. , Damarla Gowrisankar , Perez Jose M.
Published: August 2014

Using a micro-scratch tester we have determined the influence of scratch velocity on the sliding wear resistance of several thermoplastics: polystyrene (PS), styrene-acrylonitrile, polyamide 6, polyethersulfone and polysulfone. Variable velocities (from 1 to 15 mm/min) were applied under two different load configurations: progressively increasing loads from 0.03 to 30 N and multiple scratching under constant loads from 2.5 to 10 N. Penetration and residual depth were measured along a 5 mm length. In the case of PS the scanning electron microscopy images of the progressive load scratch reveal a transition from shear yielding to crazing at low velocity. In multiple scratching tests the residual depths obtained at 1 mm/min are substantially higher than those at 15 mm/min for all thermoplastics tested. This result is explained by contact heating at higher speeds resulting in increased chain relaxation capability and thus more viscoelastic recovery. Scanning probe microscopy was used in order to observe surface damages. Except for PS, all other materials at all velocities exhibit asymptotic behaviour of the residual depth as a function of the number of tests.
Magnetic colloids: preparation and biomedical applications
Authors: Elaissari Abdelhamid
Published: August 2014

Increasing interest has been focused on the preparation of magnetic latex particles and their use in biomedical diagnostics. All elaborated magnetic colloidal particles or latexes are principally used as a solid support of biomolecules involved in the specific capture of targeted biomolecules such as antigens in immunoassays (i.e., ELISA) and nucleic acid detection in ELOSA. Nowadays, the main objective in biomedical diagnosis is to enhance the sensitivity and to accelerate the procedure by elaborating new magnetic colloidal particles and diagnostic methods. The general problem in this field is related to the limited sensitivity. One possibility to partially solve it is to increase the concentration of captured targets (antigens, nucleic acids, etc.) before the specific detection step. Thus, the use of appropriate magnetic colloidal particles and methods for extraction and concentration of biomolecules is of extreme interest.