bluuebunny/crossref_metadata_2025 huggingface dataset:
Chiral discrimination of amines by anisotropic NMR parameters using chiral polyacrylamide‐based gels
Authors: Schmidt Manuel , Sun Han , Leonov Andrei , Griesinger Christian , Reinscheid Uwe M.
Published: December 2012

A new chiral alignment medium for dimethyl sulfoxide, methanol, and water as solvents was developed. Because both enantiomers of the gel are available, it is possible to enantiodiscriminate natural products such as strychnine HCl that naturally occurs as single enantiomer. With the two methods of achieving anisotropy, namely stretching and confinement, the degree of alignment can be adjusted, and the director changed from horizontal to vertical. This increases the applicability. Three compounds were enantiodiscriminated on the basis of residual dipolar coupling data: mefloquine HCl, strychnine HCl, and menthylamine HCl. Copyright © 2012 John Wiley & Sons, Ltd.
Noncovalently and covalently cross‐linked polyurethane gels as alignment media and the suppression of residual polymer signals using diffusion‐filtered spectroscopy
Authors: Kaden Peter , Freudenberger J. Christoph , Luy Burkhard
Published: December 2012

With polyurethane (PU), a novel alignment medium for organic solvents is introduced and characterized, which is very robust and easy to produce on a large scale. Linear PU already constitutes an elastomer gel with several solvents based on its ability to form hydrogen bonds. Covalent cross‐linking of the polymer with accelerated electrons provides an alignment medium with different properties. However, PU exhibits a number of undesired polymer signals in corresponding spectra, which ideally have to be removed spectroscopically. Within this context, we demonstrate the applicability of diffusion‐filtered experiments for removal of the polymer signals. Example spectra for the usefulness of PU alignment media are provided for the common test molecules strychnine and norcamphor. Copyright © 2012 John Wiley & Sons, Ltd.
Review: use of residual dipolar couplings to determine the structure of carbohydrates
Authors: Canales A. , Jiménez‐Barbero J. , Martín‐Pastor M.
Published: December 2012

Solution nuclear magnetic resonance spectroscopy is especially useful in the carbohydrate field. The measurement of residual dipolar couplings provides long‐range structural information, a valuable complement for the structural study of carbohydrates either in its free form or in the bound state to proteins. They permit to deduce the geometry and the flexibility of the glycosidic linkages, which have a major influence on the conformation of carbohydrates and their overall shape. This article reviews the current application of the residual dipolar couplings methodology to carbohydrates. Copyright © 2012 John Wiley & Sons, Ltd.
MSpin‐RDC. A program for the use of residual dipolar couplings for structure elucidation of small molecules
Authors: Navarro‐Vázquez Armando
Published: December 2012

We developed a new program, MSpin‐RDC for the analysis of residual dipolar coupling data. This software, specially designed for small molecule analysis, can directly read many molecular‐modeling and popular chemistry file formats and accept RDC values as a simple free‐format table. Alignment tensor can then be computed by singular value decomposition, as well as predicted using inertia and gyration tensor‐based methodologies. Trial structures are then ranked according to their Cornilescu's quality factor (Q) values. Analysis of multiconformational problems and fitting of RDC data to relative populations can be accomplished using the single‐tensor approximation. Copyright © 2012 John Wiley & Sons, Ltd.
Effect of Hydrogen and External Donor on the Microstructure of Polypropylene Made with a 4th Generation Ziegler–Natta Catalyst
Authors: Alshaiban Ahmad , Soares João B. P.
Published: December 2012

The effect of adding hydrogen and/or electron donor on the microstructure of polypropylene polymerized with a 4th generation Ziegler–Natta catalysts at two temperatures on the molecular weight distribution, tacticity, and crystallinity of polypropylene is thoroughly investigated in this article. Polypropylene tacticity and crystallinity increases not only when external donors are added, but also when hydrogen is used as a chain transfer agent. The molecular weight distribution of the resins is deconvoluted into several Flory's most probable distributions to show how different active site types respond to the presence of electron donor and hydrogen.

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A unified dual‐primal finite element tearing and interconnecting approach for incompressible Stokes equations
Authors: Tu Xuemin , Li Jing
Published: December 2012

A unified framework of dual‐primal finite element tearing and interconnecting (FETI‐DP) algorithms is proposed for solving the system of linear equations arising from the mixed finite element approximation of incompressible Stokes equations. A distinctive feature of this framework is that it allows using both continuous and discontinuous pressures in the algorithm, whereas previous FETI‐DP methods only apply to discontinuous pressures. A preconditioned conjugate gradient method is used in the algorithm with either a lumped or a Dirichlet preconditioner, and scalable convergence rates are proved. This framework is also used to describe several previously developed FETI‐DP algorithms and greatly simplifies their analysis. Numerical experiments of solving a two‐dimensional incompressible Stokes problem demonstrate the performances of the discussed FETI‐DP algorithms represented under the same framework.Copyright © 2012 John Wiley & Sons, Ltd.
Synthesis, characterization, and photoresponsive studies on lignin functionalized with (E)‐2‐(4‐(naphthalen‐1‐yldiazenyl)phenyl)acetic acid
Authors: Chandran Ambily , Kuriakose Sunny , Mathew Tessymol
Published: December 2012

A chromophoric system (E)‐2‐(4‐(naphthalen‐1‐yldiazenyl)phenyl)acetic acid incorporated onto a nature friendly biopolymeric core material, lignin (technical lignin, lignin sulphonic acid M.W. 52,400), and the photo responsive behavior of the product was investigated. The product was characterized by UV–visible, fluorescence, Fourier transform infrared, and nuclear magnetic resonance spectroscopic methods. The results of the studies show that the incorporation of the chromophoric system on to the lignin core enhanced the light absorption and light stabilization properties of the chromophoric system. The trans‐cis photoisomerization and the reverse cis‐trans thermal conversions were also assisted by the lignin core. The remarkable stability on irradiation shows that this is a novel photoresponsive system with excellent light fastening properties which would find application in coating materials, dyes, paints, inks, and many more. Copyright © 2012 John Wiley & Sons, Ltd.
Thermal and sonochemical degradation kinetics of poly(n‐butyl methacrylate‐co‐alkyl acrylates): Variation of chain strength and stability with copolymer composition
Authors: Bhagat Rajesh , Madras Giridhar
Published: December 2012

The thermal degradation of poly(n‐butyl methacrylate‐co‐alkyl acrylate) was compared with ultrasonic degradation. For this purpose, different compositions of poly (n‐butyl methacrylate‐co‐methyl acrylate) (PBMAMA) and a particular composition of poly(n‐butyl methacrylate‐co‐ethyl acrylate) (PBMAEA) and poly(n‐butyl methacrylate‐co‐butyl acrylate) (PBMABA) were synthesized and characterized. The thermal degradation of polymers shows that the poly(alkyl acrylates) degrade in a single stage by random chain scission and poly(n‐butyl methacrylate) degrades in two stages. The number of stages of thermal degradation of copolymers was same as the majority component of the copolymer. The activation energy corresponding to random chain scission increased and then decreased with an increase of n‐butyl methacrylate fraction in copolymer. The effect of methyl acrylate content, alkyl acrylate substituent, and solvents on the ultrasonic degradation of these copolymers was investigated. A continuous distribution kinetics model was used to determine the degradation rate coefficients. The degradation rate coefficient of PBMAMA varied nonlinearly with n‐butyl methacrylate content. The degradation of poly (n‐butyl methacrylate‐co‐alkyl acrylate) followed the order: PBMAMA < PBMAEA < PBMABA. The variation in the degradation rate constant with composition of the copolymer was discussed in relation to the competing effects of the stretching of the polymer in solution and the electron displacement in the main chain. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers
Superimposed effects in high‐shear‐rate capillary rheology of polystyrene melt
Authors: Guan Wei‐Sheng , Huang Han‐Xiong
Published: December 2012

During micro‐injection molding, the polymer melt may undergo a shear rate up to 106 s−1, at which the rheological behaviors are obviously different from those in conventional molding process. Using both online and commercial rheometers, high‐shear‐rate capillary rheology of polystyrene (PS) melt is analyzed systematically in this work. The accurate end pressure drop and pressure coefficient of viscosity are determined via the enhanced exit pressure technique. Experimental and theoretical investigations are conducted on four significant effects, that is, the dissipative heating, end pressure loss, pressure dependence, and melt compressibility in capillary flow. For the PS melt, which exhibits distinct temperature and pressure dependence of viscosity, both dissipation and end effects become pronounced as the shear rate exceeds 2 × 105 s−1. From lower to higher shear rates (103–106 s−1), the competition between dissipation and pressure effects results in the overestimation to underestimation of Bagley‐corrected pressure drop, and finally the comprehensively corrected viscosity becomes about half of the uncorrected one owing to the enhanced superimposed effects. Moreover, the compressibility shows a minor influence on the shear viscosity. Under the shear rate range investigated, the power‐law relationship is sufficient for describing the corrected viscosity curve of PS melt used. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers
Effect of lanthanum cyanurate as novel organic thermal stabilizers for polyvinyl chloride
Authors: Li Mei , Jiang Zaiyong , Liu Zhaogang , Hu Yanhong , Wang Mitang , Wang Haiou
Published: December 2012

Lanthanum cyanurate was synthesized by reacting cyanuric acid and lanthanum nitrate at basic condition and was characterized by elemental analysis and Fourier transform infrared spectroscopy. Its application as thermal stabilizer for poly(vinyl chloride) (PVC) was investigated by Congo red test and discoloration test. In comparison with other heat stabilizers, including lanthanum stearate, calcium stearate, and zinc stearate, lanthanum cyanurate exhibits high stabilizing effect with excellent initial color of PVC. The stability time reaches the maximum (80 min) when the percentage of lanthanum cyanurate in PVC is 2.5%. The combination stabilizers (LaC3N3O3/Zn(St)2 obviously increase the complete discoloration time of PVC in comparison with the stabilizer of Zn(St)2. The stability time of PVC increases from 14 min (stabilized by zinc stearate) to 26 min (stabilized by LaC3N3O3/Zn(St)2). LaC3N3O3 also shows a slightly stronger effect on tensile strength of PVC than La(St)3. Therefore, the LaC3N3O3 can be used to replace La(St)3 and serve as a costabilizer to improve stabilization efficiency of calcium/zinc stabilizers for PVC. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers
Plastisol foaming process. Decomposition of the foaming agent, polymer behavior in the corresponding temperature range and resulting foam properties
Authors: Verdu J. , Zoller A. , Marcilla A.
Published: December 2012

The decomposition of azodicarbonamide, used as foaming agent in PVC—plasticizer (1/1) plastisols was studied by DSC. Nineteen different plasticizers, all belonging to the ester family, two being polymeric (polyadipates), were compared. The temperature of maximum decomposition rate (in anisothermal regime at 5 K min−1 scanning rate), ranges between 434 and 452 K. The heat of decomposition ranges between 8.7 and 12.5 J g−1. Some trends of variation of these parameters appear significant and are discussed in terms of solvent (matrix) and viscosity effects on the decomposition reactions. The shear modulus at 1 Hz frequency was determined at the temperature of maximum rate of foaming agent decomposition, and differs significantly from a sample to another. The foam density was determined at ambient temperature and the volume fraction of bubbles was used as criterion to judge the efficiency of the foaming process. The results reveal the existence of an optimal shear modulus of the order of 2 kPa that corresponds roughly to plasticizer molar masses of the order of 450 ± 50 g mol−1. Heavier plasticizers, especially polymeric ones are too difficult to deform. Lighter plasticizers such as diethyl phthalate (DEP) deform too easily and presumably facilitate bubble collapse. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers
Synthesis, swelling capacity, and texture of polymers from monomers of sulfonic acid and acrylamide
Authors: Rosa Fátima , Bordado João , Casquilho Miguel
Published: December 2012

The monomers 2‐acrylamido‐2‐methyl‐propanosulfonic acid and acrylamide, and methyleno‐bisacrylamide (BA) whenever a crosslinker was added, were selected for the synthesis of superabsorbent polymers. Texture was observed by scanning electronic microscopy, and specific gravity and swelling were measured. The influence of synthesis conditions—polymerization technique, reaction medium pH, and BA addition—on the texture of the synthesized polymer and its influence on polymer characteristics were assessed. The tests showed that the pores' sizes and distribution in the polymer depend on the polymerization conditions. Swelling rate of the polymers, namely from inverse emulsion technique, with BA and at pH 9, is remarkably high, suiting applications. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers
Mixed monolayers of pmas with poly(styrene‐b‐methyl methacrylate) at the air/water interface
Authors: Su Hsin‐Kai , Hsu Wen‐Ping
Published: December 2012

Poly(methyl methacrylate) (PMMA) is known to be immiscible with poly(styrene) (PS) in the bulk state. Poly(ethyl methacrylate) (PEMA), poly(propyl methacrylate) (PPMA), and poly(n‐butyl methacrylate) (PBMA) are also known to be immiscible with PMMA (or PS). Therefore, PMAs (PMMA, PEMA, PPMA, and PBMA) are predicted by the mean field theory to be immiscible with poly(styrene‐b‐methyl methacrylate) (PS‐b‐PMMA) in the bulk state. However, the miscibility of PMAs with PS‐b‐PMMA may be different in the two‐dimensional state. Therefore, the mixed monolayer behavior of PMAs and PS‐b‐PMMA was investigated from the measurements of surface pressure‐area per molecule (π‐A) isotherms at three different temperatures (10°C, 25°C, and 40°C). Calculation of compressibility from isotherms provided the inflection data from maximum and minimum peaks. The miscibility and nonideality of the mixed monolayers were examined by calculating the excess area as a function of composition. Mostly, negative deviations from ideality were observed in the mixed monolayers. This is likely because of favorable interaction between PMMA and PMAs in the monolayer state. The positive deviations occurred at 40°C with PBMA at a high surface pressure. Therefore, with confinement in the two‐dimensional state, the miscibility between PMAs and PS‐b‐PMMA was greatly improved in comparison with the bulk state. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers
Efficient zinc initiators supported by NNO‐tridentate ketiminate ligands for cyclic esters polymerization
Authors: Chuang Hui‐Ju , Chen Hsiao‐Li , Huang Bor‐Hunn , Tsai Tsung‐En , Huang Pei‐Ling , Liao Tzu‐Ting , Lin Chu‐Chieh
Published: December 2012

A series of zinc benzylalkoxide complexes, [LnZn(μ‐OBn)]2 (L = L1H–L5H), supported by NNO‐tridentate ketiminate ligands with various electron withdrawing‐donating subsituents have been synthesized and characterized. X‐ray crystal structural studies revealed that complexes 2b and 4b are dinuclear bridging through the benzylalkoxy oxygen atoms with penta‐coordinated metal centers. All the metal complexes have acted as efficient initiators for the ring‐opening polymerization of L‐lactide (within 12 min, 0 °C). Remarkably, a molecular weight of PLLA up to 580,000 can be achieved using [(L5Zn(μ‐OBn)]2 (5b) as an initiator. The kinetic studies for the polymerization of L‐lactide with complex 3b at −10 °C corresponded to first‐order reactions in the monomer. The ring‐opening polymerization (ROP) of ε‐caprolactone, ε‐decalactone, β‐butyrolactone and their copolymer with complex 3b was investigated. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013
Formation of linear and cyclic polyoxetanes in the cationic ring‐opening polymerization of 3‐allyloxymethyl‐3‐ethyloxetane and subsequent postpolymerization modification of poly(3‐allyloxymethyl‐3‐ethyloxetane)
Authors: Schulte Bjoern , Dannenberg Carl A. , Keul Helmut , Möller Martin
Published: December 2012

The synthesis of 3‐allyloxymethyl‐3‐ethyloxetane (AllylEHO) and its polymerization with BF3 × Et2O is described in this study. Size exclusion chromatography (SEC) and membrane osmometry are used for the determination of molecular weights of the obtained products, ranging from Mn,SEC = 41,500‐131,500 g/mol. 1H NMR spectroscopy, SEC, as well as MALDI‐TOF MS reveal the formation of cyclic tetramer beside low, but detectable concentrations of larger cyclic oligomers as by‐products during the polymerization process. These results help to understand mechanistically why attempts for a controlled homopolymerization of AllylEHO fail and why a controlled homopolymerization of oxetanes has not been described so far in the literature. Additionally, the high versatility of allyl‐functional polyoxetane for postpolymerization modification is proven by thiol–ene reactions with 3‐mercaptopropionic acid and N‐acetyl‐L‐cysteine methyl ester. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013
H‐transfer reaction during decomposition of N‐(2‐methylpropyl)‐ N‐(1‐diethylphosphono‐2,2‐dimethylpropyl)‐N‐oxyl (SG1)‐based alkoxyamines
Authors: Edeleva Mariya , Marque Sylvain R. A. , Kabytaev Kuanish , Guillaneuf Yohann , Gigmes Didier , Bagryanskaya Elena
Published: December 2012

Thermal decomposition of four tertiary N‐(2‐methylpropyl)‐N‐(1‐diethylphosphono‐2,2‐dimethylpropyl)‐N‐oxyl (SG1)‐based alkoxyamines (SG1‐C(Me)2‐C(O)‐OR, R = Me, tBu, Et, H) has been studied at different experimental conditions using 1H and 31P NMR spectroscopies. This experiment represents the initiating step of methyl methacrylate polymerization. It has been shown that H‐transfer reaction occurs during the decomposition of three alkoxyamines in highly degassed solution, whereas no products of H‐transfer are detected during decomposition of SG1‐MAMA alkoxyamine. The value of the rate constant of H‐transfer for alkoxyamines 1 (SG1‐C(Me)2‐C(O)‐OMe) and 2 (SG1‐C(Me)2‐C(O)‐OtBu) has been estimated as 1.7 × 103 M−1s−1. The high influence of oxygen on decomposition mechanism is found. In particular, in poorly degassed solutions, nearly quantitative formation of oxidation product has been observed, whereas at residual pressure of 10−5 mbar, the main products originate from H‐atom transfer reaction. The acidity of the reaction medium affects the decomposition mechanism suppressing the H‐atom transfer. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013
Ionic networks derived from the protonation of dendritic amines with carboxylic acid end‐functionalized PEGs
Authors: González Lidia , Ladegaard Skov Anne , Hvilsted Søren
Published: December 2012

The synthesis and characterization of novel ionic networks linked by the ammonium salts of poly(propylene imine) (PPI) dendrimers of the first (PPI G1) and second (PPI G2) generation and two short bis carboxymethyl ether terminated poly(ethylene glycol)s (DiCOOH‐PEG) with different molecular weights (Mn ∼ 250 and Mn ∼ 600) are reported. Likewise, an ionic network based on PPI G1 and a long αω‐dicarboxylic acid functionalized PEG (Mn ∼ 4800) were evaluated. Simpler ionic structures based on tris(2‐aminoethyl)amine or hexamethylene diamine and the short DiCOOH‐PEGs are also investigated. The ionic structures formed were confirmed by differential scanning calorimetry, Fourier Transform Infrared spectroscopy in the attenuated‐total‐reflection mode, and 1H‐13C NMR spectroscopy. A comprehensive 1H NMR analysis revealed that only the primary amines of the PPI G1 dendrimer residing at the periphery take part in the ionic network formation. In the case of PPI G2, the picture is less clear. A thorough investigation of the thermal degradation of the utilized precursors and all the ionic materials prepared was additionally performed by thermogravimetric analysis. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013
Thermosensitive water‐soluble poly(ethylene glycol)‐based polythiophene graft copolymers
Authors: Das Sandip , Samanta Sanjoy , Chatterjee Dhruba P. , Nandi Arun K.
Published: December 2012

Diethyleneglycol methylethermethacrylate(MeO2MA) and oligoethylene glycol methylethermethacrylate(OEGMA) are polymerized on polythiophene(PT) backbone to produce water‐soluble PT‐g‐PMeO2MA(PTD) and PT‐g‐P(MeO2MA‐co‐OEGMA)(PTDO) using atom transfer radical polymerization. They are characterized by 1H NMR and GPC techniques. TEM micrographs indicate that PT‐chains self‐organize as nanospheres, and atomic force micrographs suggest that aggregated PT‐chains are present at the centre surrounded by dispersed PMeO2MA fibers producing miceller‐type aggregates. Dynamic light scattering study indicates an initial decrease followed by sharp increase of Z‐average particle size of PTD with temperature for attaining lower critical solution temperature (LCST) at 20 °C. The LCST increases with OEGMA concentration in PTDO. The temperature dependent PL emission of PTD shows a minimum at 19 °C, followed by a sharp increase till 21 °C, and in the cooling cycle, it shows a complete reversibility. In the PTDO copolymers, the PL intensity shows the hike at progressively higher temperatures due to the increase of LCST with increasing OEGMA concentration. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013
Feeding‐Gas Effects of Plasma Jets on Escherichia coli in Physiological Solutions
Authors: Baik Ku Youn , Kim Yong Hee , Ryu Young Hyo , Kwon Hye Seon , Park Gyungsoon , Uhm Han S. , Choi Eun H.
Published: December 2012

The effects of air and N2 plasma jets on Escherichia coli inside four different physiological solutions and deionized water are reported here. The feeding gases are found to influence the plasma compositions, the interactions with the liquids, and the subsequent bactericidal effects depending on the aqueous solutions to which they are exposed. Air plasma enhances the bactericidal effects of deionized water and saline by acidification. On the other hand, N2 plasma induces higher toxicity in phosphate buffered saline by generating more electrons. Little bactericidal effects of cell culture media and blood plasma may be due to the slight change in the pH and due to electron scavenging by organic components. Taken together, our study provides additional insight into the basic interactions between plasma and cells in physiological solutions.

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Chemical and Physical Sputtering of Polyethylene Terephthalate (PET)
Authors: Große‐Kreul Simon , Corbella Carles , von Keudell Achim
Published: December 2012

The polymer polyethylene terephthalate (PET) has been exposed to quantified beams of argon ions and oxygen atoms and molecules. The etch rate (ER) and the surface composition of PET thin films have been analyzed by real time in situ Fourier transform infrared spectroscopy (FTIR). After the onset of the exposure of PET to the ion beam, the ER decreases rapidly by one order of magnitude irrespective of the ion energy. This slowing down of the ER is caused by cross‐linking of the polymer surface. The steady state etch yields are generally orders of magnitude higher than predicted by computer calculations. The addition of oxygen to the particle flux is only changing the surface composition. At low ion energies, chemical sputtering dominates causing very high sputter yields. In addition, no threshold ion energy is observed.

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Antimicrobial Activity and Cyto‐Compatibility of Plasma Polymerized Zinc Acetylacetonate Thin Films
Authors: Malzahn Kerstin , Duque Luis , Ciernak Peter , Wiesenmüller Steffi , Bender Katja , Förch Renate
Published: December 2012

Plasma polymerized thin films deposited from zinc acetylacetonate in a low pressure RF capacitively coupled plasma reactor have been studied to correlate the zinc content to the metal ion release properties, antimicrobial activity and cytocompatibility. Zinc content and zinc release properties were studied using inductively coupled plasma optical emission spectroscopy (ICP‐OES) and results were correlated to those from different standard methods of surface analysis. The coatings were shown to act as a zinc reservoir, allowing for a fast release of zinc within a few hours of being in contact with aqueous solution. For all films studied a log 106 reduction in the growth of Staphylococcus aureus was observed. The results show the films to be cyto‐compatible towards NIH 3T3 mammalian cells up to a zinc content of about 5 µg/cm2.

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Optical properties of Eu‐doped NaYP2O7 under UV and X‐ray excitation
Authors: Novais Suellen Maria Valeriano , Macedo Zélia Soares
Published: December 2012

Eu‐doped NaYP2O7 polycrystalline samples were produced via sol‐gel method based on PVA. Structural investigation of calcined powders was made by X‐ray diffraction analysis. High crystalline purity was achieved when using molar ratio Na:Y:P of 1.15:1:2 and the presence of dopant caused no noticeable change on the structure. The influence of secondary phases on the optical properties of NaY0.99Eu0.01P2O7 was investigated by photoluminescence (PL) and X‐ray excited optical luminescence (XEOL). In general, each XEOL emission spectrum was similar to that obtained from PL. The spectroscopic properties measured indicate that the dopant occupies two sites of high symmetry on the host matrix and that the spurious phases significantly affect the luminescence yield. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural evolution of AlN buffer and crystal quality of GaN films on a‐ and c‐sapphire grown by metalorganic vapor phase epitaxy
Authors: Okuno Koji , Oshio Takahide , Shibata Naoki , Honda Yoshio , Yamaguchi Masahito , Tanaka Shigeyasu , Amano Hiroshi
Published: December 2012

Low‐temperature‐deposited (LT‐) AlN layers and the initial growth of GaN on a‐ and c‐sapphire have been investigated and compared. The as‐deposited LT‐AlN layers on both a‐ and c‐sapphire are composed of high‐density islands. By annealing, the islands become large. The density of islands on a‐ and c‐sapphire are 5.6 × 1010 and 7.9 × 1010 cm‐2, respectively, indicating that the evolution of the solid phase epitaxy of AlN islands induced by annealing is different on a‐ and c‐sapphire. The moiré spacings obtained by plan‐view electron microscopy reveal that the strain of the AlN islands on a‐sapphire is larger than that of islands on c‐sapphire. These results imply that development of the solid phase epitaxy is influenced by the strain. The coalescence of GaN islands grown on a‐sapphire, which has larger AlN islands, is advanced compared with that of islands on c‐sapphire. The relationship between the annealed AlN island density and the threading dislocation (TD) density in the GaN films is investigated on a‐ and c‐sapphire. The TD density of the GaN films is small when the density of annealed AlN islands is low. These results indicate that decreasing the island density of the annealed AlN layers is essential for improving the crystalline quality of GaN films. It is therefore important to control the solid phase epitaxy of LT‐AlN layers by annealing. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Role of extended defects in the transformation of InGaN/GaN multiple quantum well structure optical properties under low energy electron beam irradiation
Authors: Vergeles P. S. , Shmidt N. M. , Yakimov E. B.
Published: December 2012

It is shown that threading extended defects can enhance the excess carrier transport through the InGaN/GaN multiple quantum well (MQW) region. The enhanced excess carrier transport through a GaN film is also revealed that was explained by a carrier transport along extended defects. A possible role of threading extended defects in the low energy electron beam irradiation induced modification of electrical and optical properties in InGaN/GaN MQW structures are discussed. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
AlGaN photodetectors for the UV‐C spectral region on planar and epitaxial laterally overgrown AlN/sapphire templates
Authors: Knigge A. , Brendel M. , Brunner F. , Einfeldt S. , Knauer A. , Kueller V. , Weyers M.
Published: December 2012

We present Schottky type metal semiconductor metal (MSM) AlGaN photodetectors (PDs) suited for the ultraviolet C (UV‐C) spectral region grown on conventional planar AlN templates in comparison with epitaxial laterally overgrown (ELO) AlN templates. On planar templates solar blind MSM PDs with state‐of‐the‐art dark current in the pA range and a power independent responsivity are obtained. Using ELO templates with sapphire substrates tilted to the m direction the defect density in the absorber material is reduced compared to that for planar templates. The MSM PDs on this ELO templates exhibit photoconductive gain leading to external quantum efficiencies of up to 77 at 30 V applied bias surpassing that of the planar grown PDs by a factor of 100. In spite of the high gain these PDs also show low dark currents in the pA range up to 100 V applied bias, short switching times and two operating regimes with power independent responsivity. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electrical and optical properties of bulk GaN substrates studied by Kelvin probe and photoluminescence
Authors: McNamara J. D. , Foussekis M. A. , Baski A. A. , Li X. , Avrutin V. , Morkoç H. , Leach J. H. , Paskova T. , Udwary K. , Preble E. , Reshchikov M. A.
Published: December 2012

We have investigated the N‐ and Ga‐polar faces of bulk GaN substrates with photoluminescence (PL) and the surface photovoltage (SPV) technique using a Kelvin probe attached to an optical cryostat. Experiments were conducted in vacuum. Some of the surfaces were mechanically polished (MP), while others were epi‐ready after a chemical‐mechanical polish (CMP). From the SPV measurements, the band bending in a sample having both surfaces treated with the CMP method was calculated to be about 0.83 and 0.70 eV for the Ga‐ and N‐polar surfaces, respectively. The restoration of the SPV after ceasing the UV illumination showed that the SPV from CMP‐treated surfaces behaved as predicted by a thermionic model, whereas the SPV from MP‐treated surfaces restored with a much faster‐than‐predicted rate. This result can be interpreted by the hopping of charge carriers in the highly‐defective near‐surface layer of the MP‐treated samples. Remarkably, removing the top 700 nm defective layer by dry etching restored the quality of the electrical and optical properties of GaN. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microstructure of Mg doped GaNAs alloys
Authors: Liliental‐Weber Z. , Reis R. dos , Novikov S. V. , Yu K. M. , Levander A. X. , Dubon O. D. , Wu J. , Walukiewicz W. , Foxon C. T.
Published: December 2012

Transmission Electron Microscopy of Mg doped GaN1‐xAsx samples, grown by MBE at low temperatures, show substantial structural changes for samples that are semi‐insulating and those with high or low conductivity. The conductive samples show p‐type conductivity as evidence from the positive thermopower values. All the Mg doped samples show phase segregation: cubic GaAs and GaN grains (a mixture of cubic and some hexagonal) phases within an amorphous matrix. The best conductive samples show cubic GaAs grains with high density of stacking faults embedded into an amorphous matrix. The samples that are less conductive have lower ratio of the amorphous to the crystalline phase of the samples and much lower density of stacking faults. Higher Mg concentration is expected in the amorphous parts of the samples The semi‐insulating samples that have either low Mg concentration or low As show grains of GaAs and GaN attached to each other with no evidence of the amorphous phase between them. There are no SFs in these grains. It is possible that the presence of the GaN between the GaAs grains lead to semi‐insulating material properties since p‐type doping of GaN is more difficult. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Suppression of twin formation for the growth of InN(10‐1‐3) on GaAs(110) by metalorganic vapor phase epitaxy
Authors: Murakami Hisashi , Takenaka Sae , Hotta Tetsuro , Kumagai Yoshinao , Koukitu Akinori
Published: December 2012

The influence of hydrogen (H2) in the carrier gas on the crystalline quality as well as twin‐crystal formation were investigated in the metalorganic vapor phase epitaxy (MOVPE) of InN on GaAs(110). The inclusion of twin crystals of InN(10‐13) was suppressed by the introduction of a small amount of H2 during crystal growth. The surface morphology of the InN layer was also significantly influenced by the input partial pressure of H2 in the carrier gas. The suppression of twin‐crystal formation and improvements in the surface morphology can be explained by the differences in the stability of the In‐ and N‐polar InN{0001} asymmetric planes in the presence of H2. Both electronic and optical properties were improved by the introduction of H2, which was probably due to the reduction of impurities such as oxygen and carbon in the InN grown layer. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stratification of randomization is not required for a pre‐specified subgroup analysis
Authors: Kaiser Lee D.
Published: December 2012

Published literature and regulatory agency guidance documents provide conflicting recommendations as to whether a pre‐specified subgroup analysis also requires for its validity that the study employ randomization that is stratified on subgroup membership. This is an important issue, as subgroup analyses are often required to demonstrate efficacy in the development of drugs with a companion diagnostic. Here, it is shown, for typical randomization methods, that the fraction of patients in the subgroup given experimental treatment matches, on average, the target fraction in the entire study. Also, mean covariate values are balanced, on average, between treatment arms in the subgroup, and it is argued that the variance in covariate imbalance between treatment arms in the subgroup is at worst only slightly increased versus a subgroup‐stratified randomization method. Finally, in an analysis of variance setting, a least‐squares treatment effect estimator within the subgroup is shown to be unbiased whether or not the randomization is stratified on subgroup membership. Thus, a requirement that a study be stratified on subgroup membership would place an artificial roadblock to innovation and the goals of personalized healthcare. Copyright © 2012 John Wiley & Sons, Ltd.
Analysis error covarianceversusposterior covariance in variational data assimilation
Authors: Gejadze I. Yu. , Shutyaevb V. , Dimetc F.‐X. Le
Published: December 2012

The problem of variational data assimilation for a nonlinear evolution model is formulated as an optimal control problem to find the initial condition function (analysis). The data contain errors (observation and background errors); hence there is an error in the analysis. For mildly nonlinear dynamics the analysis error covariance can be approximated by the inverse Hessian of the cost functional in the auxiliary data assimilation problem, and for stronger nonlinearity by the ‘effective’ inverse Hessian. However, it has been noticed that the analysis error covariance is not the posterior covariance from the Bayesian perspective. While these two are equivalent in the linear case, the difference may become significant in practical terms with the nonlinearity level rising. For the proper Bayesian posterior covariance a new approximation via the Hessian is derived and its ‘effective’ counterpart is introduced. An approach for computing the mentioned estimates in the matrix‐free environment using the Lanczos method with preconditioning is suggested. Numerical examples which validate the developed theory are presented for the model governed by Burgers equation with a nonlinear viscous term.
Exploration of the reactivity of N2O5 with two Si(OH)4 monomers using electronic structure methods
Authors: Messaoudi Sabri , Bejaoui Bechir , Akrout Fourat , Bel Hassen Malika , Sammari Cherif
Published: December 2012

The heterogeneous uptake of N2O5 on mineral dust particles may play an important role in the removal of nitrogen oxides from the atmosphere. However, the reaction of N2O5 with the mineral particles is not well understood. The reaction of N2O5 with two Si(OH)4 monomers is explored using theoretical methods. This study represents a first step towards understanding the interaction of N2O5 with the hydroxyl groups of silica particles. Energies are calculated using MP2 single point calculations on the B3LYP optimized geometries and including B3LYP thermodynamic corrections. Four mechanisms are considered for the formation of two HNO3 and one H6Si2O7. The rate limiting activation barrier of the most favorable path is found to be 12.5 kcal mol−1. This reaction appears to be more favorable than the hydrolysis of N2O5 with one water molecule. These results are in agreement with experimental observations, which show that N2O5 reacts with OH groups of Saharan dust to form nitrate. © 2012 Wiley Periodicals, Inc.
Contribution of dendritic cells to measles virus induced immunosuppression
Authors: Coughlin Melissa M. , Bellini William J. , Rota Paul A.
Published: December 2012

Measles virus (MV) remains an important pathogen in children worldwide. The morbidity and mortality of MV is associated with severe immune suppression. Dendritic cells (DCs) were identified as initial target cells in vivo, and DCs were efficiently infected by MV in vitro. MV infection of DCs likely contributes to functional deficiency in these cells; therefore playing a role in MV‐induced immunosuppression. DCs appeared to mature phenotypically; however, the ability of infected cells to stimulate T cells was compromised. Phenotypic maturation of infected immature DCs was partially controlled by IFN production; however, infected DCs also maintained markers of an immature phenotype such as the continued uptake of antigen and lack of expression of chemokine receptor CCR7. Furthermore, mature DCs did not appear to maintain phenotypic maturation following infection demonstrated by decreased MHC and co‐stimulatory molecule expression. Several mechanisms of MV‐induced DC dysfunction have been suggested, each likely contributing to the immunosuppressive effect of MV‐infected DCs. Infected DCs responded aberrantly to secondary maturation stimuli such as CD40L or TLR4 stimulation. MV infection resulted in apoptosis in DC/T‐cell cocultures, which may contribute to a reduced T‐cell response. Additionally, the immunological synapse between infected DCs and T cells was compromised resulting in reduced T‐cell interaction times and activation signaling. The mechanisms of MV contribution to DC dysfunction appear multifaceted and central to MV‐induced immunosuppression. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.
Group polarization on corporate boards: Theory and evidence on board decisions about acquisition premiums
Authors: Zhu David H.
Published: December 2012

This study investigates how a fundamental group decision‐making bias referred to as group polarization can influence boards' acquisition premium decisions. The theory suggests that when prior premium experience would lead directors on average to support a relatively high premium prior to board discussions, they will support a focal premium that is even higher after discussions; but when directors' prior premium experience would lead them on average to support a relatively low premium prior to board discussions, they will support a focal premium that is even lower after discussions. Results provided strong support for the theory. Moreover, group polarization was reduced by demographic homogeneity among directors and by minority expertise but increased by board influence. This study introduces a fundamental group decision‐making bias into governance research and explains how group processes can influence network diffusions. Copyright © 2012 John Wiley & Sons, Ltd.
Plasmonic Amplifiers: Engineering Giant Light Enhancements by Tuning Resonances in Multiscale Plasmonic Nanostructures
Authors: Chen Aiqing , Miller Ryan L. , DePrince A. Eugene , Joshi‐Imre Alexandra , Shevchenko Elena , Ocola Leonidas E. , Gray Stephen K. , Welp Ulrich , Vlasko‐Vlasov Vitalii K.
Published: December 2012

The unique ability of plasmonic nanostructures to guide, enhance, and manipulate subwavelength light offers multiple novel applications in chemical and biological sensing, imaging, and photonic microcircuitry. Here the reproducible, giant light amplification in multiscale plasmonic structures is demonstrated. These structures combine strongly coupled components of different dimensions and topologies that resonate at the same optical frequency. A light amplifier is constructed using a silver mirror carrying light‐enhancing surface plasmons, dielectric gratings forming distributed Bragg cavities on top of the mirror, and gold nanoparticle arrays self‐assembled into the grating grooves. By tuning the resonances of the individual components to the same frequency, multiple enhancement of the light intensity in the nanometer gaps between the particles is achieved. Using a monolayer of benzenethiol molecules on this structure, an average SERS enhancement factor  ∼108 is obtained, and the maximum enhancement in the interparticle hot‐spots is ∼3 × 1010, in good agreement with FDTD calculations. The high enhancement factor, large density of well‐ordered hot‐spots, and good fidelity of the SERS signal make this design a promising platform for quantitative SERS sensing, optical detection, efficient solid state lighting, advanced photovoltaics, and other emerging photonic applications.
An alternative procedure for seismic evaluation and strengthening of tall buildings
Authors: Hart Gary C. , Brandow Gregg E. , Brugger Larry , Carpenter Lauren D. , Quadri Nick Delli , Huang Sampson C. , Kashefi Ifa , Kumabe Colin , Lew Marshall
Published: December 2012

The goal of existing building codes and standards for the evaluation and strengthening of existing buildings is to provide for safe buildings by prescribing loads and material properties and structural analysis methods for a broad spectrum of building heights, types and construction. Experience clearly shows that building codes and standards do not provide for the most economical, efficient and safe tall buildings because the codes are general and prescriptive in nature and do not allow the structural engineer the flexibility without significant difficulty to incorporate building‐specific applicable experience, education and new technologies. Tall buildings are really a special class of buildings that have unique qualities and characteristics. The design of tall buildings has been recognized by the structural engineering profession to require more care and effort in both design and construction because of the need to meet safety and performance requirements. This recognition is based in part on the large number of people at risk in tall buildings and also the negative financial impact on the community and the building owner. To meet this need, an alternative procedure for Seismic Evaluation and Strengthening of Existing Tall Buildings in the Los Angeles region is under development by the Los Angeles Tall Buildings Structural Design Council. This paper presents a progress report on this development. Copyright © 2012 John Wiley & Sons, Ltd.
Assembly of Bacteriophage into Functional Materials
Authors: Yang Sung Ho , Chung Woo‐Jae , McFarland Sean , Lee Seung‐Wuk
Published: December 2012

For the last decade, the fabrication of ordered structures of phage has been of great interest as a means of utilizing the outstanding biochemical properties of phage in developing useful materials. Combined with other organic/inorganic substances, it has been demonstrated that phage is a superior building block for fabricating various functional devices, such as the electrode in lithium‐ion batteries, photovoltaic cells, sensors, and cell‐culture supports. Although previous research has expanded the utility of phage when combined with genetic engineering, most improvements in device functionality have relied upon increases in efficiency owing to the compact, more densely packable unit size of phage rather than on the unique properties of the ordered nanostructures themselves. Recently, self‐templating methods, which control both thermodynamic and kinetic factors during the deposition process, have opened up new routes to exploiting the ordered structural properties of hierarchically organized phage architectures. In addition, ordered phage films have exhibited unexpected functional properties, such as structural color and optical filtering. Structural colors or optical filtering from phage films can be used for optical phage‐based sensors, which combine the structural properties of phage with target‐specific binding motifs on the phage‐coat proteins. This self‐templating method may contribute not only to practical applications, but also provide insight into the fundamental study of biomacromolecule assembly in in vivo systems under complicated and dynamic conditions.
Design, Synthesis, and Evaluation of Bioactive Small Molecules
Authors: Hua Duy H.
Published: December 2012

Collaborative research projects between chemists, biologists, and medical scientists have inevitably produced many useful drugs, biosensors, and medical instrumentation. Organic chemistry lies at the heart of drug discovery and development. The current range of organic synthetic methodologies allows for the construction of unlimited libraries of small organic molecules for drug screening. In translational research projects, we have focused on the discovery of lead compounds for three major diseases: Alzheimer's disease (AD), breast cancer, and viral infections. In the AD project, we have taken a rational‐design approach and synthesized a new class of tricyclic pyrone (TP) compounds that preserve memory and motor functions in amyloid precursor protein (APP)/presenilin‐1 (PS1) mice. TPs could protect neuronal death through several possible mechanisms, including their ability to inhibit the formation of both intraneuronal and extracellular amyloid β (Aβ) aggregates, to increase cholesterol efflux, to restore axonal trafficking, and to enhance long‐term potentiation (LTP) and restored LTP following treatment with Aβ oligomers. We have also synthesized a new class of gap‐junction enhancers, based on substituted quinolines, that possess potent inhibitory activities against breast‐cancer cells in vitro and in vivo. Although various antiviral drugs are available, the emergence of viral resistance to existing antiviral drugs and various understudied viral infections, such as norovirus and rotavirus, emphasizes the demand for the development of new antiviral agents against such infections and others. Our laboratories have undertaken these projects for the discovery of new antiviral inhibitors. The discussion of these aforementioned projects may shed light on the future development of drug candidates in the fields of AD, cancer, and viral infections.