bluuebunny/crossref_metadata_2025 huggingface dataset:
Health effects of extremely low‐frequency magnetic fields: reconsidering the melatonin hypothesis in the light of current data on magnetoreception
Authors: Vanderstraeten Jacques , Verschaeve Luc , Burda Hynek , Bouland Catherine , de Brouwer Christophe
Published: June 2012

The so‐called ‘Melatonin Hypothesis’ proposed that decreased nocturnal production of melatonin (MLT) might explain the increased risk of breast cancer that has been formerly attributed to extremely low‐frequency (ELF) magnetic fields (MF) of weak intensity. Although the risk of ELF MF upon breast cancer was later dismissed, repeated reports were published of partial inhibition of MLT secretion in rats under long‐term (≥ 4 weeks) exposure to weak ELF MF. Since 2004, however, this topic has not been experimentally studied any more. In the present study, we propose to go back to the MLT hypothesis and apply it to childhood leukemia, for which an increased risk has been robustly associated with residential exposure to ELF MF. Contrary to the original hypothesis, however, we do not consider decreased MLT levels, but disruption of circadian rhythmicity per se as the effector mechanism. Indeed, the role of the circadian timing system in the development of childhood leukemia has been well established. Motivation for going back to the MLT hypothesis comes from recent data that suggest magnetosensory disruption by ELF MF in mammals, and magnetosensitivity in humans, together with current evidence for an influence on circadian rhythmicity from disruption of non‐photic sensory stimuli of various natures. We thus suggest further study on circadian rhythmicity in humans (children if possible) under long‐term exposure to weak ELF MF. Copyright © 2012 John Wiley & Sons, Ltd.
Silver nanoparticles: a brief review of cytotoxicity and genotoxicity of chemically and biogenically synthesized nanoparticles
Authors: de Lima Renata , Seabra Amedea B. , Durán Nelson
Published: June 2012

In recent years interest in silver nanoparticles and their applications has increased mainly because of the important antimicrobial activities of these nanomaterials, allowing their use in several industrial sectors. However, together with these applications, there is increasing concerning related to the biological impacts of the use of silver nanoparticles on a large scale, and the possible risks to the environment and health. In this scenario, some recent studies have been published based on the investigation of potential inflammatory effects and diverse cellular impacts of silver nanoparticles. Another important issue related to nanoparticle toxicity in biological media is the capacity for increased damage to the genetic material, since nanoparticles are able to cross cell membranes and reach the cellular nucleus. In this regard, there is increasing interest in the analysis of potential nanoparticle genotoxicity, including the effects of different nanoparticle sizes and methods of synthesis. However, little is known about the genotoxicity of different silver nanoparticles and their effects on the DNA of organisms; thus further studies in this field are required. This mini‐review aims to present and to discuss recent publications related to genotoxicity and the cytotoxicity of silver nanoparticles in order to better understand the possible applications of these nanomaterials in a safe manner. This present work concludes that biogenic silver nanoparticles are generally less cyto/genotoxicin vivocompared with chemically synthesized nanoparticles. Furthermore, human cells were found to have a greater resistance to the toxic effects of silver nanoparticles in comparison with other organisms. Copyright © 2012 John Wiley & Sons, Ltd.
Suture pullout strength and in vitro fibroblast and RAW 264.7 monocyte biocompatibility of genipin crosslinked nanofibrous chitosan mats for guided tissue regeneration
Authors: Norowski P. A. , Mishra S. , Adatrow P. C. , Haggard W. O. , Bumgardner J. D.
Published: June 2012

Guided tissue regeneration (GTR) is a surgical technique used to direct the formation of bone in the graft space by protecting it with a barrier membrane used to exclude soft tissues during healing. Chitosan has been advocated for GTR applications because of its biocompatibility, degradability, wound healing, and osteogenic properties. In this study, electrospun chitosan membranes, crosslinked with 5 mM or 10 mM geinipin, a natural crosslinker extracted from the gardenia plant, were evaluated for suture pullout strength, crystallinity, and cytocompatibility with normal human dermal fibroblast and TIB 71™ RAW 264.7 monocyte cells. Ultimate suture pullout strength was significantly lower (51–67%) than that of commercially available collagen membranes. Crystallinity of the electrospun chitosan mats decreased upon crosslinking by 14–17% (p = 0.013). The molecular weight of the chitosan polymer was decreased by 75% during the electrospinning process. Uncrosslinked and genipin‐crosslinked chitosan mats were cytocompatible and supported fibroblast cell proliferation for 9 days. Uncrosslinked and genipin‐crosslinked membranes did not activate monocytes to produce nitric oxide (NO) in vitro in the absence of lipopolysaccharide (LPS). Finally, chitosan membranes inhibited LPS‐induced NO production of RAW 264.7 cells by 59–67% as compared to tissue culture plastic and collagen membrane. Improvements are needed in the tear strength of electrospun chitosan membranes for clinical application. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 100A:2890–2896, 2012.
Breast epithelial tissue morphology is affected in 3D cultures by species‐specific collagen‐based extracellular matrix
Authors: Dhimolea Eugen , Soto Ana M. , Sonnenschein Carlos
Published: June 2012

Collagen‐based gels have been widely used to determine the factors that regulate branching morphogenesis in the mammary gland. The patterns of biomechanical gradients and collagen reorganization influence the shape and orientation of epithelial structures in three‐dimensional (3D) conditions. We explored in greater detail whether collagen type I fibers with distinct biomechanical and fiber‐assembling properties, isolated from either bovine or rat tail tendon, differentially affected the epithelial phenotype in a tissue culture model of the human breast. Rat tail collagen fibers were densely packed into significantly longer and thicker bundles compared to those of the bovine type (average fascicle length 7.35 and 2.29 μm, respectively; p = 0.0001), indicating increased fiber alignment and biomechanical enablement in the former. MCF10A epithelial cells formed elaborated branched tubular structures in bovine but only nonbranched ducts and acini in rat tail collagen matrices. Ductal branching in bovine collagen was associated with interactions between neighboring structures mediated through packed collagen fibers; these fiber‐mediated interactions were absent in rat tail collagen gels. Normal breast fibroblasts increased the final size and number of ducts only in rat tail collagen gels while not affecting branching. Our results suggest that the species of origin of collagen used in organotypic cultures may influence epithelial differentiation into alveolar or ductal structures and the patterns of epithelial branching. These observations underscore the importance of considering the species of origin and fiber alignment properties of collagen when engineering branching organs in 3D matrices and interpreting their role in the tissue phenotype. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 100A:2905–2912, 2012.
Binding and leakage of barium in alginate microbeads
Authors: Mørch Yrr A. , Qi Meirigeng , Gundersen Per Ole M. , Formo Kjetil , Lacik Igor , Skjåk‐Bræk Gudmund , Oberholzer Jose , Strand Berit L.
Published: June 2012

Microbeads of alginate crosslinked with Ca2+ and/or Ba2+ are popular matrices in cell‐based therapy. The aim of this study was to quantify the binding of barium in alginate microbeads and its leakage under in vitro and accumulation under in vivo conditions. Low concentrations of barium (1 mM) in combination with calcium (50 mM) and high concentrations of barium (20 mM) in gelling solutions were used for preparation of microbeads made of high‐G and high‐M alginates. High‐G microbeads accumulated barium from gelling solution and contained higher concentrations of divalent ions for both low‐ and high‐Ba exposure compared with high‐G microbeads exposed to calcium solely and to high‐M microbeads for all gelling conditions. Although most of the unbound divalent ions were removed during the wash and culture steps, leakage of barium was still detected during storage. Barium accumulation in blood and femur bone of mice implanted with high‐G beads was found to be dose‐dependent. Estimated barium leakage relevant to transplantation to diabetic patients with islets in alginate microbeads showed that the leakage was 2.5 times lower than the tolerable intake value given by WHO for high‐G microbeads made using low barium concentration. The similar estimate gave 1.5 times higher than is the tolerable intake value for the high‐G microbeads made using high barium concentration. To reduce the risk of barium accumulation that may be of safety concern, the microbeads made of high‐G alginate gelled with a combination of calcium and low concentration of barium ions is recommended for islet transplantation. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 100A:2939–2947, 2012.
Biological responses of human bone marrow mesenchymal stem cells to Sr‐M‐Si (M = Zn, Mg) silicate bioceramics
Authors: Zhang Meili , Wu Chengtie , Lin Kaili , Fan Wei , Chen Lei , Xiao Yin , Chang Jiang
Published: June 2012

Strontium (Sr), Zinc (Zn), magnesium (Mg), and silicon (Si) are reported to be essential trace elements for the growth and mineralization of bone. We speculated that the combination of these bioactive elements in bioceramics may be effective to regulate the osteogenic property of bone‐forming cells. In this study, two Sr‐containing silicate bioceramics, Sr2ZnSi2O7 (SZS) and Sr2MgSi2O7 (SMS), were prepared. The biological response of human bone marrow mesenchymal stem cells (BMSCs) to the two bioceramics (in the forms of powders and dense ceramic bulks) was systematically studied. In powder form, the effect of powder extracts on the viability and alkaline phosphatase (ALP) activity of BMSCs was investigated. In ceramic disc form, both direct and indirect coculture of BMSCs with ceramic discs were used to investigate their biological response, including attachment, proliferation, ALP activity, and bone‐related genes expression. Beta‐tricalcium phosphate (β‐TCP) and akermanite (Ca2MgSi2O7, CMS) were used as control materials. The results showed that the Sr, Zn, and Si (or Sr, Mg, and Si)‐containing ionic products from SZS and SMS powders enhanced ALP activity of BMSCs, compared to those from β‐TCP. Both SZS and SMS ceramic discs supported the growth of BMSCs, and most importantly, significantly enhanced the ALP activity and bone‐related genes expression of BMSCs as compared to β‐TCP. The results suggest that the specific combination of bioactive ions (Sr, Zn, Si, e.g.) in bioceramics is a viable way to improve the biological performance of biomaterials, and the form of materials and surface properties were nonnegligible factors to influence cell response. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 100A:2979–2990, 2012.
Dendrimer building toolkit: Model building and characterization of various dendrimer architectures
Authors: Maingi Vishal , Jain Vaibhav , Bharatam Prasad V. , Maiti Prabal K.
Published: June 2012

We have developed a graphical user interface based dendrimer builder toolkit (DBT) which can be used to generate the dendrimer configuration of desired generation for various dendrimer architectures. The validation of structures generated by this tool was carried out by studying the structural properties of two well known classes of dendrimers: ethylenediamine cored poly(amidoamine) (PAMAM) dendrimer, diaminobutyl cored poly(propylene imine) (PPI) dendrimer. Using full atomistic molecular dynamics (MD) simulation we have calculated the radius of gyration, shape tensor and monomer density distribution for PAMAM and PPI dendrimer at neutral and high pH. A good agreement between the available simulation and experimental (small angle X‐ray and neutron scattering; SAXS, SANS) results and calculated radius of gyration was observed. With this validation we have used DBT to build another new class of nitrogen cored poly(propyl ether imine) dendrimer and study it's structural features using all atomistic MD simulation. DBT is a versatile tool and can be easily used to generate other dendrimer structures with different chemistry and topology. The use of general amber force field to describe the intra‐molecular interactions allows us to integrate this tool easily with the widely used molecular dynamics software AMBER. This makes our tool a very useful utility which can help to facilitate the study of dendrimer interaction with nucleic acids, protein and lipid bilayer for various biological applications. © 2012 Wiley Periodicals, Inc.
Electronic structure and thermodynamics of V2O3 polymorphs
Authors: Wessel C. , Reimann C. , Müller A. , Weber D. , Lerch M. , Ressler T. , Bredow T. , Dronskowski R.
Published: June 2012

A metastable bixbyite‐type polymorph of vanadium sesquioxide, V2O3, has recently been synthesized, and it transforms to the corundum‐type phase at temperatures around 550 °C. The possibility of a paramagnetic to canted antiferromagnetic or even spin‐glass‐like transition has been discussed. Quantum‐chemical calculations on the density‐functional theory level including explicit electronic correlation confirm the metastability as well as the semiconducting behavior of the material and predict that the bixbyite‐type structure is about 0.1 eV less stable than the well‐known corundum‐type phase. Nonetheless, quasiharmonic phonon calculations manifest that bixbyite‐type vanadium sesquioxide is a dynamically stable compound. Other possible V2O3 polymorphs are shown to be even less suitable candidates for the composition V2O3. © 2012 Wiley Periodicals, Inc.
A Mild and Highly Efficient Method for the Preparation of Silyl Ethers using Fe(HSO4)3/Et3N by Chlorosilanes
Authors: Abri Abdolreza , Assadi Mohammad Galeh , Pourreza Samira
Published: June 2012

A very efficient and mild procedure for preparation of silyl ethers from benzylic, allylic, propargilic alcohols, phenols, naphtoles and some of phenolic drugs with trimethylsilylchloride (TMSCl), triethylsilylchloride (TESCl) and t‐buthyldimethylsilyl chloride (TDSCl) ethers in the presence of Fe(HSO4)3/Et3N in room temperature in excellent yields is reported. This procedure also allows the excellent selectivity for silylation of alcohols and phenols.
Adenovirus vector‐based in vitro neuronal cell model for Huntington's disease with human disease‐like differential aggregation and degeneration
Authors: Dong Xiaomin , Zong Shan , Witting Anke , Lindenberg Katrin S. , Kochanek Stefan , Huang Bin
Published: June 2012

Background

Neuronal degeneration, in particular in the striatum, and the formation of nuclear and cytoplasmic inclusions are characteristics of Huntington's disease (HD) as a result of the expansion of a polyglutamine tract located close to the N‐terminus of huntingtin (htt). Because of the large (10‐kb) size of the htt cDNA, expression of full‐length htt in primary neurons has proved difficult in the past.

Methods

We generated a new chronic in vitro model that is based on high‐capacity adenovirus vector‐mediated transduction of primary murine striatal and cortical neurons. Because the vector has a large capacity for transport of foreign DNA, it was possible to quantitatively express in these primary cells normal and mutant full‐length htt (designed as fusion proteins with enhanced green fluorescent protein) in addition to its truncated versions. Pathological changes caused by mutant htt were characterized.

Results

The model mimicked several features observed in HD patients: prominent nuclear inclusions in cortical but not in striatal neurons, preferential neuronal degeneration of striatal neurons and neurofilament fragmentation in this cell type. Compared with expressed truncated mutant htt, the expression of full‐length mutant htt in neurons resulted in a much slower appearance of pathological changes. Different from cortical neurons, the vast majority of nuclei in striatal cells contained only diffusely distributed N‐terminal htt fragments. Cytoplasmic inclusions in both cell types contained full‐length mutant htt.

Conclusions

This model and the adenovirus vectors used will be valuable for studying the function of htt and the pathogenesis of HD at molecular and cellular levels in different neuronal cell types. Copyright © 2012 John Wiley & Sons, Ltd.
Protomers: formation, separation and characterization via travelling wave ion mobility mass spectrometry
Authors: Lalli Priscila M. , Iglesias Bernardo A. , Toma Henrique E. , de Sa Gilberto F. , Daroda Romeu J. , Silva Filho Juvenal C. , Szulejko Jan E. , Araki Koiti , Eberlin Marcos N.
Published: June 2012

Travelling wave ion mobility mass spectrometry (TWIM‐MS) with post‐TWIM and pre‐TWIM collision‐induced dissociation (CID) experiments were used to form, separate and characterize protomers sampled directly from solutions or generated in the gas phase via CID. When in solution equilibria, these species were transferred to the gas phase via electrospray ionization, and then separated by TWIM‐MS. CID performed after TWIM separation (post‐TWIM) allowed the characterization of both protomers via structurally diagnostic fragments. Protonated aniline (1) sampled from solution was found to be constituted of a ca. 5:1 mixture of two gaseous protomers, that is, the N‐protonated (1a) and ring protonated (1b) molecules, respectively. When dissociated, 1a nearly exclusively loses NH3, whereas 1b displays a much diverse set of fragments. When formed via CID, varying populations of 1a and 1b were detected. Two co‐existing protomers of two isomeric porphyrins were also separated and characterized via post‐TWIM CID. A deprotonated porphyrin sampled from a basic methanolic solution was found to be constituted predominantly of the protomer arising from deprotonation at the carboxyl group, which dissociates promptly by CO2 loss, but a CID‐resistant protomer arising from deprotonation at a porphyrinic ring NH was also detected and characterized. The doubly deprotonated porphyrin was found to be constituted predominantly of a single protomer arising from deprotonation of two carboxyl groups. Copyright © 2012 John Wiley & Sons, Ltd.
Secondary processes in atmospheric pressure chemical ionization–ion trap mass spectrometry: a case study of orotic acid
Authors: Fryčák Petr , Jirkovský Jaromír , Ranc Václav , Bednář Petr , Havlíček Vladimír , Lemr Karel
Published: June 2012

Atmospheric pressure chemical ionization is known for producing unusual artifacts of the ionization process in some cases. In this work, processes occuring in atmospheric pressure chemical ionization/MS of orotic acid that afforded ions accompanying protonated and deprotonated orotic acid molecules in the spectra were studied. Two processes ran in parallel in the ion source: decarboxylation of neutral orotic acid and collision‐induced dissociation of its protonated or deprotonated form. A procedure discerning pre‐ionization decomposition and post‐ionization dissociation by manipulating ion source parameters was proposed. Experiments with isotopically labeled solvents confirmed ion–molecule reactions of the product of collision‐induced dissociation of protonated orotic acid with solvent molecules in the ion source and even under vacuum in the ion trap. Copyright © 2012 John Wiley & Sons, Ltd.
In vitro metabolic fate of alizapride: evidence for the formation of reactive metabolites based on liquid chromatography‐tandem mass spectrometry
Authors: Aprile Silvio , Del Grosso Erika , Grosa Giorgio
Published: June 2012

The study of the formation of reactive metabolites during drug metabolism is one of the major areas of research in drug development since the link between reactive metabolites and drug adverse effects was well recognized. In particular, it has been shown that acrolein, a reactive carbonyl species sharing carbonylating and alkylating properties, binds covalently to nucleophilic sites in proteins, causing cellular damage. Alizapride, (±)‐6‐methoxy‐N‐{[1‐(prop‐2‐en‐1‐yl)‐pyrrolidin‐2‐yl]methyl}‐1H‐benzotriazole‐5‐carboxamide, is a N‐allyl containing dopamine antagonist with antiemetic properties for which no data concerning its metabolic fate are so far reported. The study of the in vitro metabolism of alizapride showed the formation of acrolein during the oxidative N‐deallylation. Moreover, the formation of an epoxide metabolite has been also described suggesting its role as a putative structural alert. The reactivity of the acrolein and the epoxide generated in alizapride metabolism was demonstrated by the formation of the corresponding adducts with nucleophilic thiols. Overall, ten metabolites have been identified and characterized by electrospray ionization tandem mass spectrometry analysis allowing to propose an in vitro metabolic scheme for alizapride. At the best of our knowledge, this is the second case of a drug involved in the generation of acrolein during its metabolism being the first represented by cyclophosphamide. Copyright © 2012 John Wiley & Sons, Ltd.
Cougars are recolonizing the midwest: Analysis of cougar confirmations during 1990–2008
Authors: LaRue Michelle A. , Nielsen Clayton K. , Dowling Mark , Miller Ken , Wilson Bob , Shaw Harley , Anderson Charles R.
Published: June 2012

Although cougars (Puma concolor) were extirpated from much of midwestern North America around 1900, hard evidence of cougar presence has increased and populations have become established in the upper portions of the Midwest during the past 20 years. Recent occurrences of cougars in the Midwest are likely due to dispersal of subadult cougars into the region from established western populations, and may be indicative of further recolonization and range expansion. We compiled confirmed locations of cougars (i.e., via carcasses, tracks, photos, video, and DNA evidence) collected during 1990–2008 in 14 states and provinces of midwestern North America. We separated our study area into 2 regions (east and west), calculated number and types of confirmations, and assessed trends in confirmations during the study period. We recorded 178 cougar confirmations in the Midwest and the number of confirmations increased during the study period (r = 0.79, P ≤ 0.001). Confirmations by state or province ranged from 1 (Kansas, Michigan, and Ontario) to 67 (Nebraska). Carcasses were the most prevalent confirmation type (n = 56). Seventy‐six percent of known‐sex carcass confirmations were males, consistent with predominantly male‐biased dispersal in cougars. More confirmations (P = 0.05) were recorded in the western region $({\bar {x}} = 19.9\pm 22.8/{\rm yr})$ than the eastern region $({\bar {x}} = 4.3\pm 3.1/{\rm yr})$. Seventy‐nine percent of cougar confirmations occurred within 50 km of highly suitable habitat (i.e., forest areas with steep terrain and low road and human densities). Given the number of cougar confirmations, the increasing frequency of occurrences, and that long‐distance dispersal has been documented via radiocollared individuals, our research suggests that cougars are continuing to recolonize midwestern North America. © 2012 The Wildlife Society.
2–Butoxyethanol and benzyl alcohol reactions with the nitrate radical: Rate coefficients and gas‐phase products
Authors: Harrison Joel C. , Wells J. R.
Published: June 2012

The bimolecular rate coefficients k and k were measured using the relative rate technique at (297 ± 3) K and 1 atmosphere total pressure. Values of (2.7 ± 0.7) and (4.0 ± 1.0) × 10−15 cm3 molecule−1 s−1 were observed for k and k, respectively. In addition, the products of 2‐butoxyethanol + NO3• and benzyl alcohol + NO3• gas‐phase reactions were investigated. Derivatizing agents O‐(2,3,4,5,6‐pentafluorobenzyl)hydroxylamine and N, O‐bis (trimethylsilyl)trifluoroacetamide and gas chromatography mass spectrometry (GC/MS) were used to identify the reaction products. For 2‐butoxyethanol + NO3• reaction: hydroxyacetaldehyde, 3‐hydroxypropanal, 4‐hydroxybutanal, butoxyacetaldehyde, and 4‐(2‐oxoethoxy)butan‐2‐yl nitrate were the derivatized products observed. For the benzyl alcohol + NO3• reaction: benzaldehyde ((C6H5)C(O)H) was the only derivatized product observed. Negative chemical ionization was used to identify the following nitrate products: [(2‐butoxyethoxy)(oxido)amino]oxidanide and benzyl nitrate, for 2‐butoxyethanol + NO3• and benzyl alcohol + NO3•, respectively. The elucidation of these products was facilitated by mass spectrometry of the derivatized reaction products coupled with a plausible 2‐butoxyethanol or benzyl alcohol + NO3• reaction mechanisms based on previously published volatile organic compound + NO3• gas‐phase mechanisms. © 2012 Wiley Periodicals, Inc.*

This article is a U.S. Government work and, as such, is in the public domain of the United States of America.

© 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 778–788, 2012
Thermal, Mechanical and Morphological Behavior of Poly(propylene)/Wood Flour Composites
Authors: Adhikari R. , Bhandari N. L. , Le H. H. , Henning S. , Radusch H.‐J. , Michler G. H. , Garda M.‐R. , Saiter J. M.
Published: June 2012

The comparative studies on the thermal, mechanical and morphological behavior of compression molded poly(propylene) (PP)/wood flour (WF) composites were performed using wood flours (WFs) of different origins. The comparison has been made on the basis of results obtained from thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and tensile testing. It has been demonstrated that an addition of 5 wt.‐% of maleic anhydride grafted polypropylene (PP‐g‐MA) has a significant effect on the morphological and thermomechanical behavior of the composites. Although, microscopic examinations revealed no significant differences in the morphology of the compatibilized composites, a remarkable improvement of thermal degradation behavior was observed. From the view point of mechanical properties, the composites with high amount of filler (60 wt.‐%) showed similar behavior irrespective of the origin of wood flour.
Novel Peroxide Containing Maleinate Surface‐Active Monomers for Obtaining Reactive Polymers
Authors: Borzenkov Mykola , Hevus Orest
Published: June 2012

Novel surface‐active monomers were synthesized by successive treatment of tert‐butylperoxy‐6‐hydroxyhexanoate with maleic anhydride, 1,3‐propane sultone and triethylamine or with maleic anhydride and poly(ethylene glycol) methyl ether. The surface‐active properties of monomers were studied. The critical micelle concentrations (cmc) as well as the surface tension at the cmc were determined for obtained monomers. The synthesized compounds were shown to be suitable reactive surfactants for obtaining styrene latexes.
Superparamagnetic Nanocomposites of Poly(vinyl alcohol‐graft‐acrylonitrile) as Carrier for Magnetically Assisted Release of Ciprofloxacin
Authors: Gupta Rashmi , Bajpai A.K.
Published: June 2012

In the present study also a superparamagnetic nanocomposite of Poly (vinyl‐ alcohol‐g‐acrylonitrile) has been designed by homogeneous impregnation of iron oxide nanoparticles into the graft polymer matrix. The so prepared nanocomposite was characterized by FT‐IR, TEM and XRD techniques and studied for water sorption behavior and magnetization properties. The superparamagnetic nanocomposite was loaded with an antibiotic drug, ciprofloxacin (CFx), and its release behavior was investigated under varying experimental conditions such as chemical composition of the matrix, pH of the release media, applied magnetic field and percent loading of the drug. The drug transport mechanism was also analyzed using Ficks power law. The drug loaded magnetic nanocomposite was also studied for antibacterial and in‐vitro blood compatible properties.
Thermal Properties Evolution of PCB FR4 Epoxy Composites for Mechatronic During Very Long Ageing
Authors: Lé‐Magda Mélanie , Dargent Eric , Youssef Boulos , Guillet Alain , Idrac Jonathan , Saiter Jean‐Marc
Published: June 2012

Very long ageing times, up to 8000 h at 110 °C, were achieved on printed circuit boards PCB FR4 Laminate commonly used in automotive design. This composite is fabricated from glass fiber embedded in a flame retardant epoxy resin. Ageing is performed in an oven under air atmosphere at a temperature lower than the glass transition temperature, thus physical ageing must take place. Thermogravimetric analysis indicates that during heating, the flame retardant interacts first with O2 atmosphere for temperature higher than 180 °C. Fourier transform infrared spectroscopic analysis shows that chemical degradation of the samples due to oxidation occurs after ageing at 110 °C for time longer than 940 h. From thermally modulated differential scanning calorimetry analysis, two different modifications of the epoxy resin are evidenced: one fraction for which oxidation modified drastically the molecular structure and one fraction which is not yet oxidized. These two fractions had different molecular mobilities leading to different molecular relaxation processes at the glass transition.
Effect of Epoxidation of Diene Component of SBS Block Copolymer on Morphology and Mechanical Properties
Authors: Pandit Rajesh , Giri Jyoti , Michler Goerg H. , Lach Ralf , Grellmann Wolfgang , Youssef Boulos , Saiter Jean Marc , Adhikari Rameshwar
Published: June 2012

In this work, the polybutadiene (PB) block of an asymmetric lamellae forming polystyrene/polybutadiene based triblock copolymer was epoxidized to different extent in order to study its effect on morphology and mechanical behaviour of the copolymer. The products were analyzed by means of different microscopic techniques, Fourier transform infrared (FTIR) spectroscopy and microhardness measurements. It was found that the microphase separation behavior and hence the mechanical properties of the materials were drastically altered through epoxidation of the diene block of the styrene/diene triblock copolymer. With the increase in the extent of epoxidation the lamellar structure changed to distorted lamellae and then to disordered domains. Consequently, inhomogeneous mechanical performance of the samples was observed at higher degree of chemical modification.
Optical Properties of Swift Heavy Ion Beam Irradiated Polycarbonate/Polystyrene Composites Films
Authors: Rathore Bhupendra Singh , Gaur Mulayam Singh , Singh Kripa Shanker
Published: June 2012

Polycarbonate/polystyrene composites films were irradiated by 55 MeV Carbon ion beam with fluence ranging from 1 × 1011 to 1 × 1013 ions/cm2. The polymer composites films were prepared by solution mixing method. The effects of ion beam on structural, optical and surface morphology of PC/PS composites films were investigated by X‐ray diffraction (XRD), UV‐visible spectroscopy (UV‐vis), Fourier Transform Infrared Spectroscopy (FT‐IR) and Optical Microscope. The XRD pattern shows the average crystallite size, percentage of crystallinity and inter‐chain separation, which decreases with increase in ion fluences. UV‐vis spectra show that the energy band gap and transmittance decreases while number of carbon atoms increases with fluences. The FT‐IR spectra evidenced very small change in cross linking and chain scissoring at high ion fluences, while the optical microscopy shows a color change with ion fluence.
Conductivity Study on PEO Based Polymer Electrolytes Containing Hexafluorophosphate Anion: Effect of Plasticizer
Authors: Sharma Jitender Paul , Yamada K. , Sekhon S. S.
Published: June 2012

PEO based polymer electrolytes containing ammonium hexafluorophosphate (NH4PF6) and hexafluorophosphoric acid (HPF6), both with PF anion have been studied. The effect of the addition of propylene carbonate (PC) to PEO‐NH4PF6 and PEO‐HPF6 has been observed to increase in ionic conductivity which is attributed to an increase in free ion concentration due to the dissociation of ion aggregates present at higher acid/salt concentrations. The plasticized polymer electrolytes containing HPF6 show relatively higher conductivity (σmax = 1.02 × 10−4 S/cm at 10 wt% HPF6) as compared to electrolytes containing NH4PF6 (σmax = 1.09 × 10−5 S/cm at 10 wt% NH4PF6). Presence of free ions, ion aggregates and their dissociation with the addition of PC has been studied by Fourier Transform Infrared Spectroscopy (FTIR). The change in amorphous phase with PC content was also studied by X‐Ray Diffraction (XRD). The variation of conductivity with temperature shows Vogel–Tammen–Fulcher (VTF) behavior, which is associated with the highly amorphous nature of electrolytes. 1H Nuclear magnetic Resonance (NMR) spectra at different temperatures shows line narrowing and suggests the onset of long range ion diffusional motion. Change in surface morphology of polymer electrolytes with the addition of PC is also checked by Scanning Electron Microscopic (SEM) studies.
High Density Polyethylene Containing Antibacterial Silver Nanoparticles for Medical Applications
Authors: Ziąbka Magdalena , Mertas Anna , Król Wojciech , Bobrowski Andrzej , Chłopek Jan
Published: June 2012

High density polyethylene (HDPE) and composites with silver nanoparticles were processed via extrusion and injection moulding. The materials thus produced were tested against Gram‐positive Staphylococcus aureus and Gram‐negative Escherichia coli. The release of silver ions Ag+ from composites was measured by means of ICP‐MS method. Surface parameters such as wettability and roughness were determined because of their effect on the most important processes at biomaterial interface. Scanning electron microscopy was used to investigate the microstructure. Durability tests of polymer and composite materials were carried out in a simulated biological solution by monitoring the pH and electrical conductivity, mass changes as well as the longitudinal ultrasonic wave measurements. Antibacterial tests prove that nanosilver modified materials have bactericidal activity against tested bacteria. Biological durability studies reveal stable behavior of incubated materials. Spectrometric analysis shows that the amount of silver release depends on the immersion time and the amount of nanopowder introduced into the polymer matrix.
Cardiovascular physiology in premotor Parkinson's disease: A neuroepidemiologic study
Authors: Jain Samay , Ton Thanh G. , Perera Subashan , Zheng Yan , Stein Phyllis K. , Thacker Evan , Strotmeyer Elsa S. , Newman Anne B. , Longstreth Will T.
Published: June 2012

Changes in cardiovascular physiology in Parkinson's disease (PD) are common and may occur prior to diagnostic parkinsonian motor signs. We investigated associations of electrocardiographic (ECG) abnormalities, orthostasis, heart rate variability, and carotid stenosis with the risk of PD diagnosis in the Cardiovascular Health Study, a community‐based cohort of older adults. ECG abnormality, orthostasis (symptomatic or asymptomatic), heart rate variability (24‐hour Holter monitoring), and any carotid stenosis (≥1%) by ultrasound were modeled as primary predictors of incident PD diagnosis using multivariable logistic regression. Incident PD cases were identified by at least 1 of the following: self‐report, antiparkinsonian medication use, and ICD‐9. If unadjusted models were significant, they were adjusted or stratified by age, sex, and smoking status, and those in which predictors were still significant (P ≤ .05) were also adjusted for race, diabetes, total cholesterol, low‐density lipoprotein, blood pressure, body mass index, physical activity, education level, stroke, and C‐reactive protein. Of 5888 participants, 154 incident PD cases were identified over 14 years of follow‐up. After adjusting models with all covariates, those with any ECG abnormality (odds ratio [OR], 1.45; 95% CI, 1.02–2.07; P = .04) or any carotid stenosis (OR, 2.40; 95% CI, 1.40–4.09; P = .001) at baseline had a higher risk of incident PD diagnosis. Orthostasis and heart rate variability were not significant predictors. This exploratory study suggests that carotid stenosis and ECG abnormalities occur prior to motor signs in PD, thus serving as potential premotor features or risk factors for PD diagnosis. Replication is needed in a population with more thorough ascertainment of PD onset. © 2012 Movement Disorder Society
Effect of through‐plane motion on left ventricular rotation: A study using slice‐following harmonic phase imaging
Authors: Brotman David , Zhang Ziheng , Sampath Smita
Published: June 2012

Noninvasive quantification of regional left ventricular rotation may improve understanding of cardiac function. Current methods used to quantify rotation typically acquire data on a set of prescribed short‐axis slices, neglecting effects due to through‐plane myocardial motion. We combine principles of slice‐following tagged imaging with harmonic phase analysis methods to account for through‐plane motion in regional rotation measurements. We compare rotation and torsion measurements obtained using our method to those obtained from imaging datasets acquired without slice‐following. Our results in normal volunteers demonstrate differences in the general trends of average and regional rotation‐time plots in midbasal slices and the rotation versus circumferential strain loops. We observe substantial errors in measured peak average rotation of the order of 58% for basal slices (due to change in the pattern of the curve), −6.6% for midventricular slices, and −8.5% for apical slices; and an average error in base‐to‐apex torsion of 19% when through‐plane motion is not considered. This study concludes that due to an inherent base‐to‐apex gradient in rotation that exists in the left ventricular, accounting for through‐plane motion is critical to the accuracy of left ventricular rotation quantification. Magn Reson Med, 2013. © 2011 Wiley Periodicals, Inc.
Integration of the computational fluid dynamics technique with MRI in aortic dissections
Authors: Karmonik Christof , Partovi Sasan , Davies Mark G. , Bismuth Jean , Shah Dipan J. , Bilecen Deniz , Staub Daniel , Noon George P. , Loebe Matthias , Bongartz Georg , Lumsden Alan B.
Published: June 2012

Short‐term and long‐term prognosis and their determining factors of Type III/Stanford B aortic dissections (TB‐AD), which separate the aorta distal at the origin of the subclavian artery into a true lumen and false lumen, have been elusive: One quarter of patients thought to be treated successfully, either by medical or by surgical means, do not survive 3 years. Unfavorable hemodynamic conditions are believed to lead to false lumen pressure increases and complications. A better characterization of TB‐AD hemodynamics may therefore impact therapeutic decision making and improve outcome. The large variations in TB‐AD morphology and hemodynamics favor a patient‐specific approach. Magnetic resonance imaging with its capability to provide high‐resolution structural images of the lumen and aortic wall and also to quantify aortic flow and kinetics of an exogenous tracer is a promising clinical modality for developing a deeper understanding of TB‐AD hemodynamics in an individual patient. With the information obtained with magnetic resonance imaging, computational fluid dynamics simulations can be performed to augment the image information. Here, an overview of the interplay of magnetic resonance imaging and computational fluid dynamics techniques is given illustrating the synergy of these two approaches toward a comprehensive morphological and hemodynamic characterization of TB‐AD. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.
Continuum large cracking in a rate‐dependent plastic–damage model for cyclic‐loaded concrete structures
Authors: Omidi Omid , Lotfi Vahid
Published: June 2012

Formulation and algorithmic treatment of a rate‐dependent plastic–damage model modified to capture large tensile cracking in cyclic‐loaded concrete structures are presented in detail for a three‐dimensional implementation. The plastic–damage model proposed by Lee and Fenves in 1998 was founded based on isotropic damaged elasticity in combination with isotropic multi‐hardening plasticity to simulate cracking and crushing of concrete under cyclic or dynamic loadings. In order that the model can capture large crack opening displacements, which are inevitable in plain concrete structures, the excessive increase in plastic strain causing unrealistic results in cyclic behaviors is prevented when the tensile plastic–damage variable controlling the evolution of tensile damage is larger than a critical value. In such a condition, the crack opening/closing mechanism becomes similar to discrete cracking. The consistent tangent operator required to accelerate convergence rate is also formulated for the large cracking state including viscoplasticity. The validation and performance of the modified algorithm implemented in a special finite element program is exemplified through several single‐element tests as well as three structural applications. The last example examines the model in the seismic fracture analysis of Koyna dam as a benchmark problem and the resulting crack profile is compared with the available experiment. The numerical experimentations well demonstrate that the developed model whose modification is necessary to properly simulate the cyclic behavior of plain concrete subjected to large tensile strains is robust and reasonably accurate. Copyright © 2012 John Wiley & Sons, Ltd.
A high‐order hybridizable discontinuous Galerkin method for elliptic interface problems
Authors: Huynh L.N. T. , Nguyen N.C. , Peraire J. , Khoo B.C.
Published: June 2012

We present a high‐order hybridizable discontinuous Galerkin method for solving elliptic interface problems in which the solution and gradient are nonsmooth because of jump conditions across the interface. The hybridizable discontinuous Galerkin method is endowed with several distinct characteristics. First, they reduce the globally coupled unknowns to the approximate trace of the solution on element boundaries, thereby leading to a significant reduction in the global degrees of freedom. Second, they provide, for elliptic problems with polygonal interfaces, approximations of all the variables that converge with the optimal order of k + 1 in the L2(Ω)‐norm where k denotes the polynomial order of the approximation spaces. Third, they possess some superconvergence properties that allow the use of an inexpensive element‐by‐element postprocessing to compute a new approximate solution that converges with order k + 2. However, for elliptic problems with finite jumps in the solution across the curvilinear interface, the approximate solution and gradient do not converge optimally if the elements at the interface are isoparametric. The discrepancy between the exact geometry and the approximate triangulation near the curved interfaces results in lower order convergence. To recover the optimal convergence for the approximate solution and gradient, we propose to use superparametric elements at the interface. Copyright © 2012 John Wiley & Sons, Ltd.
Permanent Visas and Temporary Jobs: Evidence from Postdoctoral Participation of Foreign PhDs in the United States
Authors: Lan Xiaohuan
Published: June 2012

About 75 percent of U.S.‐trained, noncitizen PhDs in science and engineering work in the United States after graduation, and 54 percent of those who stay take postdoctoral positions. The probability of postdoctoral participation is substantially higher for temporary visa holders than for permanent visa holders because of visa‐related restrictions in the U.S. labor market. To identify the causal effects of visa status on entry into a postdoctoral position, this paper uses a unique shock to visa status generated by the Chinese Student Protection Act of 1992. Eligibility for the act is used as an instrumental variable for visa status. Two‐stage least‐square estimates show that permanent visa holders are 24 percent less likely to take postdoctoral positions than temporary visa holders. The effects of a permanent visa vary considerably across research fields, but for most fields, it reduces postdoctoral participation significantly.
Improved conductive atomic force microscopy measurements on organic photovoltaic materials via mitigation of contact area uncertainty
Authors: Nikiforov Maxim P. , Darling Seth B.
Published: June 2012

Physical processes that lead to conversion of light into electrical energy inside photovoltaic devices happen at the nanoscale. Therefore, understanding of electrical properties of photovoltaic materials at this length scale is of paramount importance for improvement of device performance. In this paper, we describe and validate a new framework for high‐resolution quantitative measurements of electrical and mechanical properties of compliant materials with sub‐100‐nm resolution. Previous approaches have generally suffered from uncertainty in the quantitative level of contact between the probe and the material being measured; the methodology presented here overcomes this obstacle. We use the broadly studied ITO/PEDOT:PSS/P3HT:PC61BM system as an example to illustrate variability of chemical composition and electrical properties of the active layer at hundred‐nanometers and micrometer length scales. Copyright © 2012 John Wiley & Sons, Ltd.
Research on perfectionism and achievement motivation: implications for gifted students
Authors: Fletcher Kathryn L. , Speirs Neumeister Kristie L.
Published: June 2012

Perfectionism has been associated with a rigid adherence to impossibly high standards, an irrational importance on the attainment of these standards, and a tendency to overgeneralize failures. Researchers have primarily focused on how perfectionism predicts psychological adjustment; yet, recent research also indicates that perfectionism impacts students' achievement motivation. In this article, research on the relationship between perfectionism and achievement motivation in non‐gifted students is reviewed. Conclusions about perfectionism and achievement motivation in non‐gifted students will highlight directions for future research and implications for enhancing the achievement motivation of gifted students with perfectionism. © 2012 Wiley Periodicals, Inc.
Gifted native American students: Underperforming, under‐identified, and overlooked
Authors: Gentry Marcia , Fugate C. Matthew
Published: June 2012

There has been limited focus among researchers on the nature and needs of gifted Native American students in the past 30 years, and the work that has been done frequently generalizes findings across Native American cultures. This article reviews recent literature on Native American youth and on gifted Native American students; examines the current condition of education in the Diné (Navajo) Nation through a sociocultural motivation lens and based on work with one tribal community on this reservation; calls researchers and educators to action and to recognize that, as with all ethnic groups, many individual cultures exist within Native American populations; and offers suggestions for education personnel. © 2012 Wiley Periodicals, Inc.