bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optimisation of a Capillary Zone Electrophoresis Methodology for Simultaneous Analysis of Organic Aliphatic Acids in Extracts of Brachiaria brizantha
Authors: Vaz Fernando Antonio Simas , da Silva Patrícia Aparecida , Passos Leônidas Paixão , Heller Melina , Micke Gustavo Amadeu , Costa Ana Carolina Oliveira , de Oliveira Marcone Augusto Leal 
Published: March 2012

ABSTRACTIntroductionAluminum toxicity is commonly verified in acidic soils, and poses a severe limitation to plant growth and development. Therefore, Al complexation by the root system mucilage, Al complexation by organic compounds that are exuded by the roots and internal metabolic processes must be monitored by organic acids (OA), since they play a central role in these aluminum tolerance mechanisms.ObjectiveTo optimise a capillary zone electrophoresis method able to perform simultaneous separation of acetic, citric, formic, lactic, malic, oxalic, pyruvic, succinic, tartaric and aspartic acid in plant extract solutions.MethodologyMethod optimisation was achieved by a chemometric approach through experimental designs. The optimal condition found was: 20 mmol/L phthalic acid buffer; 0.8 mmol/L cetyltrimethyl‐ammonium bromide; pH 3.4 adjusted with tris(hydroxymethyl)aminomethane (around 16 mmol/L); −15 kV of voltage; 25 °C of cartridge temperature; indirect ultraviolet detection at 240 nm; and 25 mbar injection for 2 s, within an analysis time of 4 min.ResultsAs a repeatability test of the optimal condition, 30 replicates were carried out with the same working electrolyte, where the relative standard deviation of each peak ranged from 0.081 to 0.36% (for migration time) and from 2.4 to 4.6% (for peak area).ConclusionThe methodology was successfully applied to simultaneously determine citric, malic and aspartic acid in roots and leaves extract solutions of Brachiaria brizantha, demonstrating its usefulness to study aluminum tolerance. Copyright © 2012 John Wiley & Sons, Ltd.
N‐type solar‐grade silicon purified via the metallurgical route: characterisation and fabrication of solar cells
Authors: Schutz‐Kuchly Thomas , Sanzone Vincent , Veschetti Yannick 
Published: March 2012

ABSTRACTThis study focuses on the characterisation and the fabrication of solar cells using n‐type multicrystalline silicon purified via the metallurgical route. Electrical and chemical analyses were performed on wafers taken from several positions along the crystallised ingot. The impact of the fabrication processing steps was investigated via effective carrier lifetime measurements. Solar cells were processed, and their efficiencies were found to be dependent on the position of the wafer along the ingot height, that is, the wafer's resistivity. A maximum conversion efficiency of 15.0% was obtained on cells from the bottom part of the ingot. In this study, the minimum resistivity value of 0.4 Ω cm resistivity is given in order to reach adequate cell efficiency. Light‐soaking experiments were then performed on the fabricated cells. No significant variations of the cell performances were observed even after 110 h at 60 °C, meaning that the fabricated cells are stable under illumination. Copyright © 2012 John Wiley & Sons, Ltd.
Synthesis of twin‐tail tadpole‐shaped (cyclic polystyrene)‐ block‐[linear poly (tert‐butyl acrylate)]2 by combination of glaser coupling reaction with living anionic polymerization and atom transfer radical polymerization
Authors: Huang Bing , Fan Xiaoshan , Wang Guowei , Zhang Yannan , Huang Junlian 
Published: March 2012

AbstractThe twin‐tail tadpole‐shaped (cyclic polystyrene)‐block‐[linear poly (tert‐butyl acrylate)]2 [(c‐PS)‐b‐(l‐PtBA)2] was synthesized by combination of Glaser coupling reaction with atom transfer radical polymerization (ATRP) and living anionic polymerization (LAP). First, the telechelic PS with an active and an ethoxyethyl‐protected hydroxyl groups at both ends was prepared by LAP of St monomers using lithium naphthalenide as initiator and terminated by 1‐ethoxyethyl glycidyl ether. And the alkyne groups were introduced onto each PS end by selectively reaction of active hydroxy group with propargyl bromide in NaH/tetrahydrofuran (THF) system. Then, the intramolecular cyclization was carried out by Glaser coupling reaction in pyridine/Cu(I)Br system in air atmosphere. Finally, the macroinitiator of c‐PS with two bromine groups at the junction point was synthesized via the cleavage of ethoxyethyl group and the subsequent esterification of the deprotected hydroxyl groups with 2‐bromoisobutyryl bromide. The copolymer of (c‐PS)‐b‐(l‐PtBA)2 was obtained by ATRP of tBA monomers, and the PtBA segment was also hydrolyzed for (cyclic polystyrene)‐block‐(linear polyacrylic acid)2 [(c‐PS)‐b‐(l‐PAA)2]. The target copolymers and all intermediates were well characterized by GPC, MALDI‐TOF MS, and 1H NMR in detail. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012
Strain‐induced crystallization and mechanical properties of functionalized graphene sheet‐filled natural rubber
Authors: Ozbas Bulent , Toki Shigeyuki , Hsiao Benjamin S. , Chu Benjamin , Register Richard A. , Aksay Ilhan A. , Prud'homme Robert K. , Adamson Douglas H. 
Published: March 2012

AbstractThe effects of functionalized graphene sheets (FGSs) on the mechanical properties and strain‐induced crystallization of natural rubber (NR) are investigated. FGSs are predominantly single sheets of graphene with a lateral size of several hundreds of nanometers and a thickness of 1.5 nm. The effect of FGS and that of carbon black (CB) on the strain‐induced crystallization of NR is compared by coupled tensile tests and X‐ray diffraction experiments. Synchrotron X‐ray scattering enables simultaneous measurements of stress and crystallization of NR in real time during sample stretching. The onset of crystallization occurs at significantly lower strains for FGS‐filled NR samples compared with CB‐filled NR, even at low loadings. Neat‐NR exhibits strain‐induced crystallization around a strain of 2.25, while incorporation of 1 and 4 wt % FGS shifts the crystallization to strains of 1.25 and 0.75, respectively. In contrast, loadings of 16 wt % CB do not significantly shift the critical strain for crystallization. Two‐dimensional (2D) wide angle X‐ray scattering patterns show minor polymer chain alignment during stretching, in accord with previous results for NR. Small angle X‐ray scattering shows that FGS is aligned in the stretching direction, whereas CB does not show alignment or anisotropy. The mechanical properties of filled NR samples are investigated using cyclic tensile and dynamic mechanical measurements above and below the glass transition of NR. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012
A Permafrost Probability Model for the Southern Yukon and Northern British Columbia, Canada
Authors: Bonnaventure Philip P. , Lewkowicz Antoni G. , Kremer Marian , Sawada Michael C. 
Published: March 2012

ABSTRACTPermafrost maps are needed for infrastructure planning, climatic change adaptation strategies and northern development but often lack sufficient detail for these purposes. The high‐resolution (30 x 30 m grid cells) probability model for the southern Yukon and northern British Columbia presented in this paper (regional model) is a combination of seven local empirical‐statistical models, each developed from basal temperature of snow measurements in winter and ground‐truthing of frozen‐ground presence in summer. The models were blended using a distance‐decay power approach to generate a map of permafrost probability over an area of almost 500 000 km2 between 59°N and 65°N. The result is broadly similar to previous permafrost maps with an average permafrost probability of 58 per cent for the region as a whole. There are notable differences in detail, however, because the main predictive variable used in the local models is equivalent elevation, which incorporates the effects of gentle or inverted surface lapse rates in the forest zone. Most of the region shows permafrost distribution patterns that are non‐linear, resembling those from continental areas such as Mongolia. Only the southwestern area shows a similar mountain permafrost distribution to that in the European Alps with a well‐defined lower limit and a linear increase in probability with elevation. The results of the modelling can be presented on paper using traditional classifications into permafrost zones but given the level of detail, they will be more useful as an interactive online map. Copyright © 2012 John Wiley & Sons, Ltd.
Robust design and optimization of retroaldol enzymes
Authors: Althoff Eric A. , Wang Ling , Jiang Lin , Giger Lars , Lassila Jonathan K. , Wang Zhizhi , Smith Matthew , Hari Sanjay , Kast Peter , Herschlag Daniel , Hilvert Donald , Baker David 
Published: March 2012

AbstractEnzyme catalysts of a retroaldol reaction have been generated by computational design using a motif that combines a lysine in a nonpolar environment with water‐mediated stabilization of the carbinolamine hydroxyl and β‐hydroxyl groups. Here, we show that the design process is robust and repeatable, with 33 new active designs constructed on 13 different protein scaffold backbones. The initial activities are not high but are increased through site‐directed mutagenesis and laboratory evolution. Mutational data highlight areas for improvement in design. Different designed catalysts give different borohydride‐reduced reaction intermediates, suggesting a distribution of properties of the designed enzymes that may be further explored and exploited.
Ab initio protein structure assembly using continuous structure fragments and optimized knowledge‐based force field
Authors: Xu Dong , Zhang Yang 
Published: March 2012

AbstractAb initio protein folding is one of the major unsolved problems in computational biology owing to the difficulties in force field design and conformational search. We developed a novel program, QUARK, for template‐free protein structure prediction. Query sequences are first broken into fragments of 1–20 residues where multiple fragment structures are retrieved at each position from unrelated experimental structures. Full‐length structure models are then assembled from fragments using replica‐exchange Monte Carlo simulations, which are guided by a composite knowledge‐based force field. A number of novel energy terms and Monte Carlo movements are introduced and the particular contributions to enhancing the efficiency of both force field and search engine are analyzed in detail. QUARK prediction procedure is depicted and tested on the structure modeling of 145 nonhomologous proteins. Although no global templates are used and all fragments from experimental structures with template modeling score >0.5 are excluded, QUARK can successfully construct 3D models of correct folds in one‐third cases of short proteins up to 100 residues. In the ninth community‐wide Critical Assessment of protein Structure Prediction experiment, QUARK server outperformed the second and third best servers by 18 and 47% based on the cumulative Z‐score of global distance test‐total scores in the FM category. Although ab initio protein folding remains a significant challenge, these data demonstrate new progress toward the solution of the most important problem in the field. Proteins 2012; © 2012 Wiley Periodicals, Inc.
Anisotropic strain in α‐plane GaN and polarization dependence of the Raman peaks
Authors: Katsikini M. , Arvanitidis J. , Christofilos D. , Ves S. , Dimitrakopulos G. P. , Tsiakatouras G. , Tsagaraki K. , Georgakilas A. 
Published: March 2012

AbstractThe strain anisotropy of a‐plane GaN epilayers is studied by polarization‐dependent Raman spectroscopy. The intensity dependence of the A1(TO), E1(TO) and $E_{2}^{2} $ Raman peaks for an almost strain‐free epilayer is well explained by using Raman tensors of C6v symmetry. However, the corresponding angular dependence for anisotropically strained GaN with |εxx − εyy|∼6 × 10−3 (where x||a and y||m axes) dictates the use of a perturbation term of C2v symmetry that accounts for the orthorhombic distortion of the hexagonal unit cell. The consideration of this term elucidates the appearance of the $E_{2}^{2} $ mode for such epilayer orientations where it is forbidden by the hexagonal symmetry.
Epitaxial La0.7Sr0.3MnO3 thin films grown on SrTiO3 buffered silicon substrates by reactive molecular‐beam epitaxy
Authors: Méchin L. , Adamo C. , Wu S. , Guillet B. , Lebargy S. , Fur C. , Routoure J.‐M. , Mercone S. , Belmeguenai M. , Schlom D. G. 
Published: March 2012

AbstractLa0.7Sr0.3MnO3 (LSMO) thin films (with a thickness of 10, 20, 60, 75, and 100 nm) were grown on SrTiO3 (STO)‐buffered silicon (001) substrates by reactive molecular‐beam epitaxy. X‐ray diffraction (XRD) revealed the heterostructures to be fully epitaxial with orientation relationship (001) LSMO || (001) STO || (001) Si and [100] LSMO || [100] STO || [110] Si. Root mean square roughness was about 0.5 nm as measured by atomic force microscopy (AFM) for films of 10–75 nm thicknesses, and about 1 nm for the 100 nm thick LSMO film. Normalized Hooge parameters in the (0.95 ± 0.25) × 10−30–(3.41 ± 0.71) × 10−30 m3 range were measured at 300 K, which are comparable to the noise level typically measured in the best LSMO films on (001) STO substrates. Overall these very low noise LSMO films with thicknesses in the 10–100 nm range grown on STO/Si showed properties rivaling those of LSMO films deposited on (001) STO single crystal substrates, thus demonstrating their potential use for LSMO‐based devices on silicon substrates.
Different electronic transport regimes in the quasi‐two‐dimensional organic conductors κ‐(BEDT‐TTF)2X
Authors: Müller Jens , Brandenburg Jens , Schweitzer Dieter , Schlueter John A. 
Published: March 2012

AbstractWe study the low‐frequency dynamical properties of correlated charge carriers in various of the quasi‐two‐dimensional organic charge‐transfer salts κ‐(BEDT‐TTF)2X by means of fluctuation (noise) spectroscopy. Close to the critical endpoint of the Mott metal‐insulator transition, a pronounced increase of the 1/f‐noise level accompanied by a substantial shift of spectral weight to low frequencies indicates a sudden increase of the time scale of the charge fluctuations. For the less correlated, more metallic materials, we find a crossover/transition from hopping transport of more‐or‐less localized carriers at elevated temperatures to a low‐temperature regime, where a metallic coupling of the layers allows for coherent interlayer transport of delocalized electrons.
Crystal structure and band parameters of mixed crystals derived from quantum spin liquid β′‐EtMe3Sb[Pd(dmit)2]2 (dmit = 1,3‐dithiol‐2‐thione‐4,5‐dithiolate)
Authors: Kato Reizo , Fukunaga Takeo , Yamamoto Hiroshi M. , Ueda Kohei , Hengbo Cui 
Published: March 2012

AbstractA molecular Mott insulator β′‐EtMe3Sb[Pd(dmit)2]2 with a quasi‐triangular lattice of a dimer unit [Pd(dmit)2] exhibits quantum spin liquid (QSL) behavior. We introduced Me4Sb+ or Et2Me2Sb+ to the cation site of this anion radical salt without altering its crystal symmetry. The mixing ratio and lattice parameters of these mixed crystals can be continuously tuned. We calculated intermolecular transfer integrals between highest occupied molecular orbitals (HOMOs) based on structural data. Increasing the number of ethyl groups at the cation site reduces the anisotropy of the triangular lattice, and the dimer units form an almost regular triangular lattice in pure Et2Me2Sb salt. In this process, the Pd(dmit)2 molecule is slightly curved to exhibit a crescent shape. This distortion plays an important role in tuning the interdimer transfer integrals.
Spectroscopic characterization of charge order fluctuations in BEDT‐TTF metals and superconductors
Authors: Girlando A. , Masino M. , Kaiser S. , Sun Y. , Drichko N. , Dressel M. , Mori H. 
Published: March 2012

AbstractThe charge‐fluctuating and charge‐ordered states in metallic, insulating and superconducting bis(ethylenedithio)tetrathiafulvalene (BEDT‐TTF) salts are characterized through the analysis of the infrared (IR) spectral region relevant to the CC antisymmetric stretch, b1ν22. This spectral region shows dramatic changes in band intensity and band‐shape by varying the temperature. The observed spectral features can be understood on the basis of an extension of the well‐known Kubo model for the spectral signatures of an equilibrium between two states. The two‐orders of magnitude increase in the IR oscillator strength of the b1ν22 mode upon ionization has also to be taken into account.magnified image
BEDT‐TTF CC antisymmetric stretch, b1ν22.
A note on atomic density
Authors: Ramírez Guillermo , López Rafael , Ema Ignacio , Fernández Rico Jaime 
Published: March 2012

AbstractIn atomic systems, electron density has a simple finite expansion in spherical harmonics times radial factors. The difficulties in the calculation of some radial factors are illustrated in the low‐lying states of the carbon atom.Single‐particle methods such as Hartree–Fock and approximate density functional theory cannot ensure the correct expansion of the density in spherical harmonics. Wave‐function methods are appropriate but, as some expansion terms are entirely due to correlation, these methods only will give correct results for high‐quality variational functions. Using full‐configuration integration (CI), all the terms predicted by the theory appear and are not negligible but the convergence of the term due to correlation toward its correct value is uncertain even for very large CI spaces. © 2012 Wiley Periodicals, Inc.
External source method for Kubo‐transformed quantum correlation functions
Authors: Horikoshi Atsushi 
Published: March 2012

AbstractWe revisit the external source method for Kubo‐transformed quantum correlation functions recently proposed by Krishna and Voth. We derive an exact formula and show that the Krishna–Voth formula can be derived as an approximation of our formula. Some properties of this approximation are clarified through a model calculation of the position autocorrelation function for a one‐dimensional harmonic oscillator. A key observation is that the Krishna–Voth correlation function has a term that behaves as the secular term in perturbation theory. © 2012 Wiley Periodicals, Inc.
Hartree–Fock calculation for excited states
Authors: Tassi M. , Theophilou Iris , Thanos S. 
Published: March 2012

AbstractThe Hartree–Fock (HF) method, widely used for the calculation of ground state properties, in recent years has been extended for calculating excited states. In this article, we develop an approach, which does not require time consuming calculations and can give a good approximation for the excitation energies. The method is based on the fact that the subspaces of the occupied and virtual orbitals are mutually orthogonal. We test the accuracy of our method by evaluating the excited state wavefunctions and the corresponding energies for the Li, N, F, Ne, and Na atoms and for the BeH and CH molecules, and we found good agreement with configuration interaction and experimental results. © 2012 Wiley Periodicals, Inc.
Successful full‐scale enhanced anaerobic dechlorination at a NAPL strength 1,1,1‐TCA source area
Authors: Fam Sami A. , Falatko David M. , McGillicuddy Glenn , Pon George , Burkhardt Louis J. , Hone Jonathan 
Published: March 2012

AbstractBioremediation of 1,1,1‐trichloroethane (TCA) is more challenging than bioremediation of other chlorinated solvents, such as tetrachloroethene (PCE) and trichloroethene (TCE). TCA transformation often occurs under methanogenic and sulfate‐reducing conditions and is mediated by Dehalobacter. The source area at the project site contains moderately permeable medium sand with a low hydraulic gradient and is approximately 0.5 acre. TCA contamination generally extended to 35 feet, with the highest concentrations at approximately 20 feet. The concentrations then decreased with depth; several wells contained 300 to 600 mg/L of TCA prior to bioremediation. The area of treatment also contained 2 to 30 mg/L of TCE from an upgradient source. Initial site groundwater conditions indicated minimal biotic dechlorination and the presence of up to 20 mg/L of nitrate and 90 mg/L of sulfate. Microcosm testing indicated that TCA dechlorination was inhibited by the site's relatively low pH (5 to 5.5) and high TCA concentration. After the pH was adjusted and TCA concentrations were reduced to less than 35 mg/L (by dilution with site water), dechlorination proceeded rapidly using whey (or slower with sodium lactate) as an electron donor. Throughout the remediation program, increased resistance to TCA inhibition (from 35 to 200 mg/L) was observed as the microbes adapted to the elevated TCA concentrations. The article presents the results of a full‐scale enhanced anaerobic dechlorination recirculation system and the successful efforts to eliminate TCA‐ and pH‐related inhibition. © 2012 Wiley Periodicals, Inc.
A distribution‐matching method for parameter estimation and model selection in computational biology
Authors: Lillacci Gabriele , Khammash Mustafa 
Published: March 2012

SUMMARYThe determination of the model parameters is a central challenge in computational modeling of biological systems. Typically, only a fraction of the parameters (such as kinetic rate constants) is experimentally measured, whereas the rest is fitted. The fitting process is usually based on experimental time course measurements of observables, which are used to assign parameter values that minimize some measure of the error between these measurements and the corresponding model prediction. The data, which can come from real‐time polymerase chain reaction (PCR), enzymatic reactions, flow cytometry, etc., tend to be very noisy, but the statistics of the noise can often be inferred by performing calibration procedures. In this paper, we show how the knowledge of the properties of the noise, expressed in terms of its cumulative distribution function, can be used to validate or invalidate the estimates provided by an upstream state observer (a particle filter) and to refine them in case they turn out not to be satisfactory. Furthermore, we show how the same tools can be used to discriminate among alternative models of the same biological process. We demonstrate these ideas on a simple gene expression model, and we show how the proposed method is able to handle estimation problems that cannot be effectively solved by classical techniques such as least‐squares estimation. Copyright © 2012 John Wiley & Sons, Ltd.
Model predictive tracking control for a linear system under time‐varying input constraints
Authors: Wada N. , Tomosugi H. , Saeki M. 
Published: March 2012

SUMMARYIn this paper, we propose a tracking control law for a linear dynamical system under time‐varying input constraints. The proposed control law consists of a dual‐mode model predictive control (MPC) law and a target recalculation mechanism. As the terminal controller of the dual‐mode MPC, we propose a saturation‐level‐dependent gain‐scheduled feedback control law that ensures closed‐loop stability against arbitrary change of the position limit of the actuators. We also present conditions that guarantee feasibility and stability of the control algorithm under time‐varying input constraints. The control algorithm is reduced to an online optimization problem under linear matrix inequality constraints. Copyright © 2012 John Wiley & Sons, Ltd.