bluuebunny/crossref_metadata_2025_split huggingface dataset:
Homologous Copolymerization Route to Functional and Biocompatible Polyvinylpyrrolidone
Authors: Tardajos Myriam G. , Nash Maria , Rochev Yury , Reinecke Helmut , Elvira Carlos , Gallardo Alberto 
Published: February 2012

AbstractLinear multifunctional polyvinylpyrrolidone (PVP) chains bearing carboxylate (COO−) or/and sulfonate (SO3−) groups are prepared by standard radical copolymerization of homologous vinylpyrrolidone (VP) and the VP derivatives 3‐carboxyvinylpyrrolidone (VPC) and 3‐sulfoalkylvinylpyrrolidone (VPS). Functional PVP networks with homogeneous crosslinking density are also prepared using a new homologous water‐compatible VP‐R‐VP crosslinker. This homologous approach for the preparation of functionalized PVP systems is compared theoretically with the preparation of VP with commercial acrylic comonomers bearing similar functionalities. All the linear chains and networks are tested under basic in vitro cell cultures.
Molecular Weight Distribution of Linear Chains in Step‐Growth Polymerization Under the Influence of Cyclization Reactions
Authors: Wutz Christoph , Kricheldorf Hans R. 
Published: February 2012

AbstractTwo different equations are presented describing the frequency distribution (fl) of linear chains in step‐growth (SG) polymerizations. Two related equations for the weight distribution (wl) are formulated as well. All equations contain either an exponent α that represents the reaction rates (or probabilities) of chain growth versus cyclization reactions or they contain a cyclization factor β′. Plots of fl and wl versus conversion or degree of polymerization are presented and discussed. Distribution curves of individual oligomers versus conversion and versus β′ are described. Furthermore, the consequences for hyperbranched polymers resulting from polycondensations of abn monomers are discussed. Analogous to Flory's theory all equations concern kinetically controlled SG polymerizations. magnified image
Exploiting packet‐sampling measurements for traffic characterization and classification
Authors: Tammaro Davide , Valenti Silvio , Rossi Dario , Pescapé Antonio 
Published: February 2012

SUMMARYThe use of packet sampling for traffic measurement has become mandatory for network operators to cope with the huge amount of data transmitted in today's networks, powered by increasingly faster transmission technologies. Therefore, many networking tasks must already deal with such reduced data, more available but less rich in information. In this work we assess the impact of packet sampling on various network monitoring‐activities, with a particular focus on traffic characterization and classification. We process an extremely heterogeneous dataset composed of four packet‐level traces (representative of different access technologies and operational environments) with a traffic monitor able to apply different sampling policies and rates to the traffic and extract several features both in aggregated and per‐flow fashion, providing empirical evidences of the impact of packet sampling on both traffic measurement and traffic classification. First, we analyze feature distortion, quantified by means of two statistical metrics: most features appear already deteriorated under low sampling step, no matter the sampling policy, while only a few remain consistent under harsh sampling conditions, which may even cause some artifacts, undermining the correctness of measurements. Second, we evaluate the performance of traffic classification under sampling. The information content of features, even though deteriorated, still allows a good classification accuracy, provided that the classifier is trained with data obtained at the same sampling rate of the target data. The accuracy is also due to a thoughtful choice of a smart sampling policy which biases the sampling towards packets carrying the most useful information. Copyright © 2012 John Wiley & Sons, Ltd.
High Cytotoxic Activity of Phosphonium Salts and Their Complementary Selectivity towards HeLa and K562 Cancer Cells: Identification of Tri‐n‐butyl‐n‐hexadecylphosphonium bromide as a Highly Potent Anti‐HeLa Phosphonium Salt
Authors: Bachowska Barbara , Kazmierczak‐Baranska Julia , Cieslak Marcin , Nawrot Barbara , Szczęsna Dorota , Skalik Joanna , Bałczewski Piotr 
Published: February 2012

AbstractQuaternary ammonium and phosphonium salts have been screened for their toxic effect on HeLa and K562 cancer cell lines, as well as on normal HUVEC cells. Tri‐n‐butyl‐n‐hexadecylphosphonium bromide, the first phosphonium salt with a halogen anion tested against HeLa cells, was 12 times more potent (IC50 <5 μM after 24 and 48 h) than the clinically used reference compound cisplatin and 17 times more potent than tri‐n‐hexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide, which, to the best of our knowledge, is the first phosphonium salt to be evaluated in HeLa cells. However, it was inactive against K562 cells (24 and 48 h). According to a caspase‐3/7 assay, its toxicity has not been connected with the induction of apoptosis. In contrast, triphenylalkylphosphonium iodides with shorter C1–5 alkyl chains were inactive against HeLa cells but very active against K562 cells (IC50=6–10 μM after 48 h). Phosphonium cations with halide counterions proved to be more potent than those with (CF3SO2)2N− as the anion, as in the anticancer agent NSC 747251, or other anions in molecules with similar alkyl chain lengths. On the other hand, a series of ammonium salts containing a short methylthiomethyl or methoxymethyl side chain revealed low cytotoxicity (IC50 >500 μM after 24 and 48 h) against both HeLa and K562 cancer cell lines as well as normal HUVEC cells, showing that the nontoxic N+CH2YMe (Y=S, O) structural motif in ammonium salts could be suitable for further optimization and development, especially in transfection experiments.
Hot‐embossing experiments of polymethyl methacrylate across the glass transition temperature with variation in temperature and hold times
Authors: Singh Kamakshi , Dupaix Rebecca B. 
Published: February 2012

AbstractHot‐embossing (HE) experiments were conducted on polymethyl methacrylate (PMMA) across its glass transition temperature from 92 to 142°C. The glass transition temperature (Tg) of the PMMA used in this study was ∼ 102°C. The polymer samples were embossed to a depth of 0.8 mm (800 μm). The experiments were carried out at various temperatures for different hold times of 30, 90, and 180 sec during the embossing process. A few additional experiments were conducted at 142°C with cooling of the samples as well. The force required for embossing and the final depth of the embossed features were analyzed. Polymers, including PMMA, show significantly different material behavior around and above Tg. The same was seen in the aforementioned tests; the trends observed for the force as well as the final depth changed considerably around 122°C (Tg + 20). These findings will be used in developing material models for use in simulating the hot‐embossing process. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers
Experimental investigation on the role of PVA in eliminating inhibition phenomenon of carbon black during the synthesis of polystyrene/carbon black composite particles
Authors: Yan Juntao , Wang Chunlei , Gao Yan , Zheng Zaihang , Cheng Zhiqiang , Cui Xuejun , Wang Hongyan 
Published: February 2012

AbstractIn this study, the role of polyvinyl alcohol (PVA) in eliminating the inhibition phenomenon of modified light‐weight carbon black (CB) during the synthesis of polystyrene/modified light‐weight carbon black (PS/MLCB) composite particles was examined. It was interesting to note that the polymerization time was largely shortened in the presence of a certain PVA. And the effect of PVA dosage on the polymerization time and the macromorphology of obtained PS/MLCB composite particles were systematically investigated, as well as the correlation between PVA dosage, polymerization time, and MLCB content. In addition, the potential mechanism about the role of PVA in eliminating the inhibition phenomenon of MLCB during the suspension polymerization of styrene was also proposed and analyzed in detail. The PS/MLCB composites particles were studied in terms of surface morphology, thermal stability, and molecular weight. Scanning electron microscopy images of the resulting PS/MLCB composite particles demonstrated that CB was well dispersed in the PS matrix. And the thermal stability of obtained PS/MLCB composite particles was significantly enhanced with the incorporation of MLCB, and increased with the increasing content of MLCB. This synthesis technique brought about a promising future in the large‐scale production of black expandable polystyrene. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers
Nanocomposites of poly(m‐xylene diamide) with polyhedral oligomeric silsesquioxane, montmorillonite, and their combination: Structure and properties
Authors: Magniez K. , Fox Bronwyn L. , Looney Mark G. 
Published: February 2012

AbstractIn this work, nanocomposites of poly (m‐xylene diamide) (MXD6) with dodecaphenyl polyhedral oligomeric silsesquioxane (POSS), montmorillonite (MMT) and their combination (MMT‐POSS) were produced by melt‐compounding and their structure–property relationships were established. The montmorillonite was found to be homogeneously dispersed affording intercalated disordered structures whilst the distribution and dispersion of the POSS was rather skewed with the presence of phase separated crystalline aggregates of up to several hundred nanometers. Significant differences in properties were observed depending on the type of nanoscale filler present in the nanocomposites. The montmorillonite provided some improvements in stiffness and dynamic response of MXD6. POSS on the other hand improved the ductility of MXD6 and had a plasticizing effect. It has been suggested that there might be a lubricating action at the interface inducing better molecular motion between polymer chains of MXD6. By combining MMT and POSS, the properties of the corresponding nanocomposites were found to be intermediate. The thermal stability of MXD6 was enhanced in the nanocomposites although a negative deviation from the theoretical model was observed when POSS was present in the nanocomposites. This observation underlies some antagonistic effects which have been attributed to the presence of catalytic benzene radicals during thermal degradation. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers
Shear flow of molten polymer in melt blowing
Authors: Xin Sanfa , Wang Xinhou 
Published: February 2012

AbstractBesides the air flow field, the flow field of molten polymer plays a key role in fiber formation in the melt‐blowing (MB) process. In this article, the flow field of molten polymer was discussed, and its effects on the fiber microstructures were studied through theory and experiments. First, this field was supposed to be a kind of shear flow field. Two equations were introduced and solved. Then, analyzing the solutions combining with the actual melt‐blown practice, we concluded that the distribution profile of this flow field was a series of inverse parabolic in the course of the polymer stream attenuating. Further inferring from this flow pattern, we could also assume that there could have been a novel cross‐sectional microstructures in the melt‐blown fibers. Finally, the comparison experiments concerning the MB and its fibers were designed and carried out. The results indicated that the shear flow field could be qualitatively described by the equations, and the assumptions about the microstructures are basically in agreement with the experimental results. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers
Crystallization of poly(3‐hydroxybutyrate) with stereocomplexed polylactide as biodegradable nucleation agent
Authors: Chang Ling , Woo Eamor M. 
Published: February 2012

AbstractCrystallization kinetics behavior and morphology of poly(3‐hydroxybutyrate) (PHB) blended with of 2–10 wt% loadings of poly(L‐ and D‐lactic acid) (PLLA and PDLA) stereocomplex crystallites, as biodegradable nucleating agents, were studied using differential scanning calorimetry, polarizing‐light optical microscopy (POM), and wide‐angle X‐ray diffraction (WAXD). Blending PLLA with PDLA at 1:1 weight ratio led to formation of stereocomplexed PLA (sc‐PLA), which was incorporated as small crystalline nuclei into PHB for investigating melt‐crystallization kinetics. The Avrami equation was used to analyze the isothermal crystallization of PHB. The stereocomplexed crystallites acted as nucleation sites in blends and accelerated the crystallization rates of PHB by increasing the crystallization rate constant k and decreasing the half‐time (t1/2). The PHB crystallization was nucleated most effectively with 10 wt% stereocomplexed crystallites, as evidenced byPOM results. The sc‐PLA complexes (nucleated PHB crystals) exhibit much small spherulite sizes but possess the same crystal cell morphology as that of neat PHB based on the WAXD result. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers
Mechanical and morphological properties of poly(butylene adipate‐co‐terephthalate) and poly(lactic acid) blended with organically modified silicate layers
Authors: Shahlari Mahin , Lee Sunggyu 
Published: February 2012

AbstractPoly(butylene adipate‐co‐terephthalate) (PBAT) is a biodegradable polymer with high ultimate elongation but low modulus. This work studied the addition of a rigid bio‐based and biodegradable polymer, poly(lactic acid) (PLA), along with organically modified silicate layers as a conceivable means to improve the modulus of PBAT. Blending with PLA would also reduce both the cost of the ultimate blend and its dependence on nonrenewable resources. Compounds of PBAT with PLA and organically modified silicate layers showed significantly improved tensile and flexural strength resulting in enhanced thermomechanical performances compared to neat PBAT. The state of clay dispersion was evaluated using common analytical techniques such as transmission electron microscopy, X‐ray diffraction, and rheometry. The clay platelets were partially dispersed in a PBAT and PLA phase and a large portion of the platelets were located at the interface. The incorporation of organoclay reduced the dispersed phase domain (i.e., PLA) size significantly. The smaller PLA size however, did not translate into better elongational properties. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers
Effects of the aliphatic/aromatic structure on the miscibility, thermal, optical, and rheological properties of some polyimide blends
Authors: Cosutchi Andreea Irina , Nica Simona‐Luminita , Hulubei Camelia , Homocianu Mihaela , Ioan Silvia 
Published: February 2012

AbstractTwo binary polyimide (PI) blends having a common monomer (diamine or dianhydride) were prepared. The first system was composed of PIs obtained from an alicyclic and flexible dianhydride, namely 5‐(2,5‐dioxotetrahydrofurfuryl)‐3‐methyl‐3‐cyclohexene‐1,2‐dicarboxylic acid anhydride (DOCDA) and two aromatic diamines: 4,4′‐oxydianiline (ODA) and p‐phenylenediamine, respectively. In the second system, ODA was combined with DOCDA and (hexafluoroisopropyldiene)diphthalic dianhydride (6FDA). Films of the resulted blends were transparent, suggesting their homogeneity. According to differential scanning calorimetry data, the existence of a single Tg intermediate to those of the pure PIs confirmed the miscibility of blends. Incorporation of aliphatic and asymmetric DOCDA moieties, hexafluoropropyldiene groups and ether linkages in the molecular structure of PIs reduced the charge transfer interactions and significantly increased transparency and optical gap energy, especially for the poly(DOCDA‐ODA)/poly(6FDA‐ODA) blend. These interactions are also reflected in viscosity dependence on shear rate, indicating that they are slightly stronger when the aromatic 6FDA component prevails. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers
Global overview on grid‐parity
Authors: Breyer Christian , Gerlach Alexander 
Published: February 2012

ABSTRACTGrid‐parity is a very important milestone for further photovoltaic (PV) diffusion. A grid‐parity model is presented, which is based on levelized cost of electricity (LCOE) coupled with the experience curve approach. Relevant assumptions for the model are given, and its key driving forces are discussed in detail. Results of the analysis are shown for more than 150 countries and a total of 305 market segments all over the world, representing 98.0% of world population and 99.7% of global gross domestic product. High PV industry growth rates enable a fast reduction of LCOE. Depletion of fossil fuel resources and climate change mitigation forces societies to internalize these effects and pave the way for sustainable energy technologies. First grid‐parity events occur right now. The 2010s are characterized by ongoing grid‐parity events throughout the most regions in the world, reaching an addressable market of about 75–90% of total global electricity market. In consequence, new political frameworks for maximizing social benefits will be required. In parallel, PV industry tackle its next milestone, fuel‐parity. In conclusion, PV is on the pathway to become a highly competitive energy technology. Copyright © 2012 John Wiley & Sons, Ltd.
On the determination of the emitter saturation current density from lifetime measurements of silicon devices
Authors: Mäckel Helmut , Varner Kenneth 
Published: February 2012

ABSTRACTContactless photoconductance measurements are commonly used to extract the emitter saturation current density (Joe) for crystalline silicon samples containing an emitter on the surface. We review the physics behind the analysis of Joe and compare the commonly used approximations with more generalised solutions using two‐dimensional device simulations. We quantify errors present in such approximations for different test conditions involving varying illumination conditions and surface properties in samples with the same emitter on both sides. The simulated Joe obtained from the dark hole current from the emitter into the bulk is nearly the same as the simulated Joe determined by photoconductance measurements of the rear diffusion. The simulated Joe at the front emitter is equivalent to that at the rear emitter only when the sample is subject to a nearly constant and flat generation profile. For illumination conditions including visible light, the simulated Joe at the front emitter is smaller than the simulated Joe at the rear emitter. Both Joe at the rear emitter and from the dark hole current in the emitter remain nearly constant over a wide range of base doping densities. The approximations used for the determination of Joe from photoconductance measurements make Joe dependent on the excess minority carrier density. Lifetime measurements demonstrate that, even in high‐quality silicon, Joe should be determined from the analytical solution as a function of excess minority carrier density including Shockley‐Read‐Hall recombination. Copyright © 2012 John Wiley & Sons, Ltd.
Oxygen permeability in thermoplastic polyurethanes
Authors: Wang Yuxin , Gupta Mohit , Schiraldi David A. 
Published: February 2012

AbstractThe thermal and oxygen transport properties of a series of thermoplastic polyurethanes (TPUs) based on 4,4′‐methylene diisocyanate (MDI) and 1,4‐butanediol (BD) as hard segments, and poly(tetramethylene glycol) (PTMG) or poly(butylene adipate) (PA) as soft segments, are studied. Oxygen permeabilities (P) of both polyester‐based and polyether‐based TPUs increase with decreasing hard segment fractions. Oxygen solubility (S) and diffusivity (D) can be derived from permeation curves. S correlates with the amount of excess free volume as determined by the difference between glass‐transition and testing temperatures (i.e., the degree of super cooling) and decreases with the increased Tg in polyester‐based TPUs. The intensity of low temperature gamma transition reflects the activation energy for D; the higher the intensity is, the lower D is annealed TPU samples exhibited higher oxygen permeabilities as well as lower storage moduli at room temperature, despite modest increases in overall crystallinity. Dedensification of the soft segment phase during annealing/crystalline phase growth is the most likely explanation for loss of mechanical and barrier properties after annealing as partially confirmed by Fourier transform infrared spectroscopy. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012
Atmospheric Pressure Pulsed Plasma Copolymerisation of Maleic Anhydride and Vinyltrimethoxysilane: Influence of Electrical Parameters on Chemistry, Morphology and Deposition Rate of the Coatings
Authors: Manakhov Anton , Moreno‐Couranjou Maryline , Boscher Nicolas D. , Rogé Vincent , Choquet Patrick , Pireaux Jean‐Jacques 
Published: February 2012

AbstractTuning of the electrical parameter (e.g. power and pulsed discharge) of an Atmospheric Pressure Dielectric Barrier Discharge (AP‐DBD) plasma of Maleic Anhydride (MA) and vinyltrimethoxysilane (VTMOS) allows the formation of coatings with different combination of anhydride/carboxylic group surface density, morphology and deposition rate. Pulsing of the discharge favours the incorporation of MA with a high structural retention, leading to coatings with a chemical composition similar to the expected conventional MA‐VTMOS copolymer one. A kinetic model based on the free radical polymerisation is developed to correlate the carboxylic groups density on the plasma functionalised surface and the duration of the plasma off‐time.magnified image
Glycine to glutamic acid misincorporation observed in a recombinant protein expressed by Escherichia coli cells
Authors: Huang Yunping , O'Mara Brian , Conover Matthew , Ludwig Richard , Fu Jinmei , Tao Li , Li Zheng Jian , Rieble Siegfried , Grace Michael J. , Russell Reb J. 
Published: February 2012

AbstractA novel amino acid misincorporation, in which the intended glycine (Gly) residues were replaced by a glutamic acid (Glu), was observed in a recombinant protein expressed by Escherichia coli. The misincorporation was identified by peptide mapping and liquid chromatography–tandem mass spectrometric analysis on proteolyzed peptides of the protein and verified using the corresponding synthetic peptides containing the misincorporated residues. Analysis of the distribution of the misincorporated residues and their codon usage shows strong correlation between this misincorporation and the use of rarely used codon within the E. coli expression system. Results in this study suggest that the usage of the rare codon GGA has resulted in a Glu for Gly misincorporation.
Characterization of deamidation of barstar using electrospray ionization quadrupole time‐of‐flight mass spectrometry, which stabilizes an equilibrium unfolding intermediate
Authors: Jha Santosh Kumar , Deepalakshmi Putchen Dakshinamoorthy , Udgaonkar Jayant B. 
Published: February 2012

AbstractDeamidation of asparaginyl residues is a common posttranslational modification in proteins and has been studied extensively because of its important biological effects, such as those on enzymatic activity, protein folding, and proteolytic degradation. However, characterization of the sites of deamidation of a protein has been a difficult analytical problem. In this study, mass spectrometry has been used as an analytical tool to characterize the deamidation of barstar, an RNAse inhibitor. Upon incubation of the protein at alkaline pH for 5 h, intact mass analysis of barstar, using electrospray ionization quadrupole time‐of‐flight mass spectrometry (ESI QToF MS), indicated an increase in the mass of +2 Da, suggesting possible deamidation of the protein. The sites of deamidation have been identified using the conventional bottom‐up approach using a capillary liquid chromatography connected on line to an ESI QToF mass spectrometer and top down approach by direct infusion of the intact protein and fragmenting inside MS. These chemical modifications are shown to lead to stabilization of an unfolding intermediate, which can be observed in equilibrium unfolding studies.