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Two-step Method (two-step + method)
Selected AbstractsTwo-step method for precise calculation of core properties in moleculesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2005A. V. Titov Abstract Precise calculations of core properties in heavy-atom systems that are described by the operators heavily concentrated in atomic cores, such as hyperfine structure and P,T-parity nonconservation effects, require accounting for relativistic effects. Unfortunately, four-component calculation of molecules containing heavy elements is very consuming already at the stages of calculation and transformation of two-electron integrals with a basis set of four-component spinors. In turn, the relativistic effective core potential (RECP) calculations of valence (spectroscopic, chemical, etc.) properties of molecules are very popular, because the RECP method allows one to treat quite satisfactorily the correlation and relativistic effects for the valence electrons of a molecule and to reduce significantly the computational efforts. The valence molecular spinors are usually smoothed in atomic cores, and, as a result, direct calculation of electronic densities near heavy nuclei is impossible. In this paper, the methods of nonvariational and variational one-center restoration of correct shapes of four-component spinors in atomic cores after a two-component RECP calculation of a molecule are discussed. Their efficiency is illustrated in correlation calculations of hyperfine structure and parity nonconservation effects in heavy-atom molecules YbF, BaF, TlF, and PbO. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source] Chemical Vapor Deposition Repair of Graphene Oxide: A Route to Highly-Conductive Graphene MonolayersADVANCED MATERIALS, Issue 46 2009Vicente López Highly conductive chemically-derived graphene can be synthesized using an efficient two-step method starting from graphene oxide. The key strategy involves the use of a CVD process to heal defects contained within the monolayers, which imparts a two order of magnitude enhancement of electrical conductivity over the merely reduced samples. [source] Simplified intersubject averaging on the cortical surface using SUMAHUMAN BRAIN MAPPING, Issue 1 2006Brenna D. Argall Abstract Task and group comparisons in functional magnetic resonance imaging (fMRI) studies are often accomplished through the creation of intersubject average activation maps. Compared with traditional volume-based intersubject averages, averages made using computational models of the cortical surface have the potential to increase statistical power because they reduce intersubject variability in cortical folding patterns. We describe a two-step method for creating intersubject surface averages. In the first step cortical surface models are created for each subject and the locations of the anterior and posterior commissures (AC and PC) are aligned. In the second step each surface is standardized to contain the same number of nodes with identical indexing. An anatomical average from 28 subjects created using the AC,PC technique showed greater sulcal and gyral definition than the corresponding volume-based average. When applied to an fMRI dataset, the AC,PC method produced greater maximum, median, and mean t -statistics in the average activation map than did the volume average and gave a better approximation to the theoretical-ideal average calculated from individual subjects. The AC,PC method produced average activation maps equivalent to those produced with surface-averaging methods that use high-dimensional morphing. In comparison with morphing methods, the AC,PC technique does not require selection of a template brain and does not introduce deformations of sulcal and gyral patterns, allowing for group analysis within the original folded topology of each individual subject. The tools for performing AC,PC surface averaging are implemented and freely available in the SUMA software package. Hum Brain Mapp, 2005. © 2005 Wiley-Liss, Inc. [source] High-resolution, monotone solution of the adjoint shallow-water equationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 2 2002Brett F. Sanders Abstract A monotone, second-order accurate numerical scheme is presented for solving the differential form of the adjoint shallow-water equations in generalized two-dimensional coordinates. Fluctuation-splitting is utilized to achieve a high-resolution solution of the equations in primitive form. One-step and two-step schemes are presented and shown to achieve solutions of similarly high accuracy in one dimension. However, the two-step method is shown to yield more accurate solutions to problems in which unsteady wave speeds are present. In two dimensions, the two-step scheme is tested in the context of two parameter identification problems, and it is shown to accurately transmit the information needed to identify unknown forcing parameters based on measurements of the system response. The first problem involves the identification of an upstream flood hydrograph based on downstream depth measurements. The second problem involves the identification of a long wave state in the far-field based on near-field depth measurements. Copyright © 2002 John Wiley & Sons, Ltd. [source] A Novel Hydrogel with High Mechanical Strength: A Macromolecular Microsphere Composite Hydrogel,ADVANCED MATERIALS, Issue 12 2007T. Huang A novel hydrogel with a new, well- defined network structure is prepared through a two-step method in which the radiation-peroxidized macromolecular microspheres act as both initiators and crosslinkers. The macromolecular microsphere composite hydrogel (see figure) can effectively dissipate applied mechanical stress and has extremely high mechanical strength. Some of the hydrogels can nearly completely recover their original shapes, even after an extremely high strain (99.7%) in compression tests. [source] Synthesis and characterization of new polyurethane based on polycaprolactoneJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010El Miloud Maafi Abstract Different polyurethane (PU) were synthesized from ,-polycaprolactone diol, 4,4,-diphenyl methane diisocyanate (MDI) and bis(2-hydroxyethyl)terephthalate (BHET), using a two-step method and a one-step method providing regular and random distributions of starting monomers in the PU chains. Even with an identical molar monomer composition, the properties of obtained PU are different depending on the method of synthesis. The structure of PU was characterized by 1H and 13C-NMR and Fourier transform infrared spectroscopy (FTIR). The thermomechanical properties of synthesized PU were also studied demonstrating the influence of aromatic ring in the macromolecular chain. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Bioactive and mechanically strong Bioglass®-poly(D,L -lactic acid) composite coatings on surgical suturesJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2006Q. Z. Chen Abstract New coating processes have been investigated for degradable (Vicryl®) and nondegradable (Mersilk®) sutures with the aim to develop Bioglass® coated polymer fibers for wound healing and tissue engineering scaffold applications. First, the aqueous phase of a Bioglass® particle slurry was replaced with a poly(D,L -lactic acid) (PDLLA) polymer dissolved in solvent dimethyle carbonate (DMC) to act as third phase. SEM observations indicated that this alteration significantly improved the homogeneity of the coatings. Second, a new coating strategy involving two steps was developed: the sutures were first coated with a Bioglass®,PDLLA composite film followed by a second PDLLA coating. This two-step process of coating has addressed the problem of poor adherence of Bioglass® particles on suture surfaces. The coated sutures were knotted to determine qualitatively the mechanical integrity of the coatings. The results indicated that adhesion strength of coatings obtained by the two-step method was remarkably enhanced. A comparative assessment of the bioactivity of one-step and two-step produced coatings was carried out in vitro using acellular simulated body fluid (SBF) for up to 28 days. Coatings produced by the two-step process were found to have similar bioactivity as the one-step produced coatings. The novel Bioglass®/PDLLA/Vicryl® and Bioglass®/PDLLA/Mersilk® composite sutures are promising bioactive materials for wound healing and tissue engineering applications. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006 [source] The Heckman Correction for Sample Selection and Its CritiqueJOURNAL OF ECONOMIC SURVEYS, Issue 1 2000Patrick Puhani This paper gives a short overview of Monte Carlo studies on the usefulness of Heckman's (1976, 1979) two-step estimator for estimating selection models. Such models occur frequently in empirical work, especially in microeconometrics when estimating wage equations or consumer expenditures. It is shown that exploratory work to check for collinearity problems is strongly recommended before deciding on which estimator to apply. In the absence of collinearity problems, the full-information maximum likelihood estimator is preferable to the limited-information two-step method of Heckman, although the latter also gives reasonable results. If, however, collinearity problems prevail, subsample OLS (or the Two-Part Model) is the most robust amongst the simple-to-calculate estimators. [source] Synthesis and second-order nonlinear optical properties of multifunctional polysiloxanes with sulfonyl-based chromophoresJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 7 2005Jianli Hua Abstract Two new polysiloxanes (P1 and P2) with a high density of sulfonyl-based chromophores were prepared by a new two-step method. Poly[methyl-3-(9-carbazolyl)propyl siloxane] was partially formulated by the standard Vilsmeier reaction, and formyl groups of high reactivity were condensed with cyanoacetylated chromophores; this yielded polysiloxanes P1 and P2 in almost complete conversions. Their structures were verified with 1H NMR, IR, and ultraviolet,visible spectra. P1 and P2 exhibited good solubility in common organic solvents and were thermally stable. The maximum absorptions appeared at about 452 and 390 nm for P1 and P2, respectively, in tetrahydrofuran; they were blueshifted about 42 and 8 nm, respectively, in comparison with those of the corresponding chromophores with a nitro acceptor and resulted in a wider transparency window. The P1 values of the nonlinear optical coefficient (d33), measured by in situ second harmonic generation, was 16.2 pm/V. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1317,1324, 2005 [source] Synthesis and properties of new ultraviolet,blue-emissive fluorene-based aromatic polyoxadiazoles with confinement moietiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 5 2003Nam Choul Yang Abstract Three families of fluorene,oxadiazole-based polymers with confinement moieties have successfully been prepared by the two-step method for polyoxadiazole synthesis. These polymers show good solubility in common organic solvents, high thermal stability, and strong violet and blue photoluminescence in solution and as films, respectively. Their low-lying highest occupied molecular orbital/lowest unoccupied molecular orbital energy levels originate from the electron deficiency of an oxadiazole moiety, and this suggests that they may be useful for blue-emitting and electron-transport/hole-blocking layers in electroluminescent devices. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 674,683, 2003 [source] Isolation and purification of macrocyclic components from Penicillium fermentation broth by high-speed counter-current chromatographyJOURNAL OF SEPARATION SCIENCE, JSS, Issue 2 2010Xiang Gao Abstract In this paper, high-speed counter-current chromatography (HSCCC), assisted with ESI-MS, was first successfully applied to the preparative separation of three macrolide antibiotics, brefeldin A (12.6,mg, 99.0%), 7,- O -formylbrefeldin A (6.5,mg, 95.0%) and 7,- O -acetylbrefeldin A (5.0,mg, 92.3%) from the crude extract of the microbe Penicillium SHZK-15. Considering the chemical nature and partition coefficient (K) values of the three target compounds, a two-step HSCCC isolation protocol was developed in order to obtain products with high purity. In the two-step method, the crude ethyl acetate extract was first fractionated and resulted in two peak fractions by HSCCC using solvent system n -hexane/ethyl acetate/methanol/water (HEMWat) (3:7:5:5,v/v/v/v), then purified using solvent systems HEMWat (3:5:3:5,v/v/v/v) and HEMWat (7:3:5:5,v/v/v/v) for each fraction. The purities and structures of the isolated compounds were determined by HPLC, X-ray crystallography, ESI-MS and NMR. The results demonstrated that HSCCC is a fast and efficient technique for systematic isolation of bioactive compounds from the microbes. [source] Hydrothermal Synthesis of Thin Films of Barium Titanate Ceramic Nano-Tubes at 200°CJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2003Nitin P. Padture§ A novel, low-temperature synthesis method for producing BaTiO3 thin films patterned in the form of nano-tubes ("honeycomb") on Ti substrates is reported. In this two-step method, the Ti substrate is first anodized to produce a surface layer (,200,300-nm thickness) of amorphous titanium oxide nano-tube (,100-nm diameter) arrays. In the second step, the anodized substrate is subjected to hydrothermal treatment in aqueous Ba(OH)2, where the nano-tube arrays serve as templates for their hydrothermal conversion to polycrystalline BaTiO3 nano-tubes. This opens the possibility of tailoring the nano-tube arrays and of using various precursor solutions and their combinations in the hydrothermal bath, to produce ordered, patterned thin-film structures of various Ti-containing ceramics. These could find use not only in a variety of electronic device applications but also in biomedical applications, where patterned thin films are also desirable. [source] Facile Synthesis of Spherical Polyelectrolyte Brushes as Carriers for Conducting Polymers to be Used in Plastic ElectronicsMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 18 2009Jianjun Wang Abstract A two-step method for the preparation of spherical polyelectrolyte brushes (SPBs) has been developed. Copolymerization of styrene and divinyl benzene at the particle surface resulted in a large number of accessible vinyl groups. These vinyl groups reacted with sodium styrene sulfonate to give SPBs. The SPBs were used as carriers for conducting polymers resulting in redispersible conducting inks with good film forming properties. Direct current (DC) conductivity of the polypyrrole (PPy) loaded samples showed a percolating behavior as probed by impedance spectroscopy. Finally, device performance of organic light-emitting diodes based on the conducting thin films assembled from the PPy loaded particles was tested. [source] Enhancement of Thermal Conductivity with CuO for NanofluidsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 1 2006M.-S. Liu Abstract The enhancement of the thermal conductivity of ethylene glycol in the presence of copper oxide (CuO) is investigated. CuO nanofluids are prepared in a two-step method. No surfactant is employed as a dispersant. The volume fraction of CuO nanoparticles suspended in ethylene glycol liquid is below 5,vol.-%. The crystalline phases of the CuO powders are measured with x-ray diffraction patterns (XRD). CuO nanoparticles are examined using scanning electron microscopy (SEM) to determine their microstructure. The thermal conductivities of the CuO suspensions are measured by a modified transient hot wire method. The viscosity was measured with a viscosity instrument. The results show that CuO nanofluids with low concentrations of nanoparticles have considerably higher thermal conductivities than the identical ethylene glycol base liquids without solid nanoparticles. The thermal conductivity ratio improvement for CuO nanofluids is approximately linear with the volume fraction of nanoparticles. For CuO nanoparticles at a volume fraction of 0.05 (5,vol-.%) thermal conductivity was enhanced by up to 22.4,%. CuO nanofluids thus have good potential for effective heat transfer applications. [source] High affinity, high efficiency fibre-reactive dyesCOLORATION TECHNOLOGY, Issue 4 2006Brent Smith A straightforward two-step method for modifying commercial dichlorotriazine-based fibre-reactive dyes prior to their use in the dyeing process can greatly improve affinity and fixation efficiency on cotton, and reduce the salt requirements. The modification used in this study involved prereacting the commercial dyes with either cysteine or cysteamine followed by reaction of the resulting intermediate with cyanuric chloride. Cotton fabric dyed with the modified dyes had technical properties that were essentially equal to those obtained from the unmodified commercial dyes. [source] | |||||||||||||