Orthogonal grid generation for Navier–Stokes computations

Body conforming orthogonal grids were generated using a fast hyperbolic method for aerofoils, and were used to solve the Navier–Stokes equation in the generalized orthogonal system for the first time for time accurate simulation of incompressible flow. For grid generation, the Beltrami equation and the definition equation for the orthogonality are solved using a finite difference method. The grids generated around aerofoils by this method have better orthogonality than the results published by earlier investigators. The Navier–Stokes equation at Reynolds numbers of 3000 and 35 000 for NACA 0012 and NACA 0015 respectively, have been solved as an application. The obtained results match quite well with the corresponding experimental results. © 1998 John Wiley & Sons, Ltd.     

Determination of the 15N chemical shift anisotropy in natural abundance samples by proton-detected 3D solid-state NMR under ultrafast MAS of 70 kHz

Chemical shift anisotropy (CSA) is a sensitive probe of electronic environment at a nucleus, and thus, it offers deeper insights into detailed structural and dynamic properties of different systems, for example, chemical, biological, and materials. Over the years, massive efforts have been made to develop recoupling methods that reintroduce CSA interaction under magic angle spinning (MAS) conditions. Most of them require slow or moderate MAS (≤20 kHz) and isotopically enriched samples. On the other hand, to the best of the authors' knowledge, no ¹³C or ¹⁵N CSA recoupling schemes at ultrafast MAS (≥60 kHz) suitable for cost-effective natural abundant samples have been developed. We present here a proton-detected 3D ¹⁵N CS/¹⁵N CSA/¹H CS correlation experiment which employs ¹H indirect detection for sensitivity enhancement and a γ-encoded -symmetry-based CSA recoupling scheme. In particular, two different symmetries, that is, R8³₇ and R10⁴₉, are first tested, in a 2D ¹⁵N CSA/¹H CS version, on [U-¹⁵N]-L-histidine·HCl·H₂O as a model sample under 70 kHz MAS. Then the 3D experiment is applied on glycyl-L-alanine at natural abundance, resulting in site-resolved ¹⁵N CSA lineshapes from which CSA parameters are retrieved by SIMPSON numerical fittings. We demonstrate that this 3D R-symmetry-based pulse sequence is highly robust with respect to wide-range offset mismatches and weakly dependent to rf inhomogeneity within mis-sets of ±10% from the theoretical value.     

Manganese(II) complexes of 5-(4-pyridyl), 5-phenyl and 5-(4-methoxy-phenyl)-1,3,4-oxadiazole-2-thione containing 2, 2′-bipyridyl/ethylenediamine: synthesis,spectral, and X-ray characterization

Three new mixed ligand complexes [Mn(4-pytone)₂(bipy)₂]bipy (1), [Mn(pot)₂(en)₂] (2) and [Mn(4-mot)₂(en)₂] (3) (4-pytone = 5-(4-pyridyl)-1,3,4-oxadiazole-2-thione, pot = 5-phenyl-1,3,4-oxadiazole-2-thione, 4-mot = 5-(4-methoxy-phenyl)-1,3,4-oxadiazole-2-thione) have been prepared containing bipy/en as coligands. The starting material potassium N-(aryl-carbonyl)-hydrazinecarbodithioates (RCONHNHCSSK) underwent cyclization during complexation in the presence of bipy or en to give the corresponding 5-aryl-1,3,4-oxadiazole-2-thiones. The complexes have been characterized by physicochemical techniques and single crystal X-ray structure determination. In all cases, the manganese has a six coordinate octahedral arrangement coordinated by 4N atoms of two bipy/en and two covalently bonded N atoms of the oxadiazole-2-thione anions.     

Tautomeric forms of adenine: Vertical ionization energies and Dyson orbitals

For the MP2/6‐311++g(2df,p) optimized geometry of all the 14 adenine tautomers, the first three vertical ionization energies have been calculated using several electron propagator decouplings. The corresponding Dyson orbitals provide detailed insight into the role of structural variations in different adenine tautomers. Changes in the electron binding energies and the corresponding Dyson orbital amplitudes have been correlated with tautomeric proton shifts and changes in conjugation patterns. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Identifying the Bond Responsible for the Fluorescence Modulation in an Amyloid Fibril Sensor

An ultrafast intramolecular bond twisting process is known to be the responsible mechanism for the sensing activity of the extensively used amyloid fibril sensor thioflavin T (ThT). However, it is not yet known which one of the two possible single bonds in ThT is actually involved in the twisting process. To resolve this fundamental issue, two derivatives of ThT have been designed and synthesized and subsequently their photophysical properties have been studied in different solvents. It is understood from the present study that the rotation around the central C? C single bond, and not that around the C? N single bond, is primarily responsible for the sensor activity of ThT. Detailed viscosity‐dependent fluorescence studies revealed that the ThT derivative with restricted C? N bond rotation acts as a better sensor than the derivative with free C? N bond rotation. The better sensory activity is directly correlated with a shorter excited‐state lifetime. Results obtained from the photophysical studies of the ThT derivatives have also been supported by the results obtained from quantum chemical calculations.     

Tuning magnetism of MnO by doping with 2p elements

We show that the antiferromagnetic coupling between Mn atoms in MnO can be tuned to a ferromagnetic one by doping it with a small concentration of 2p elements like boron, carbon and nitrogen. Our ab initio density functional calculations in the Hubbard U framework show that the coupling between Mn atoms turns ferromagnetic for 3 at% B doping. B is found to be the most effective one in stabilizing ferromagnetism. We discuss the role of 2p states of the dopant atoms to explain the trend of ferromagnetism in MnO.     

In situ production of CuS particles in polymer electrolyte matrix for mixed ion+electron conduction

Composites of polymer electrolyte polyethylene oxide (PEO) complexed with NH₄ClO_4, (PEO:NH₄ClO₄), having different weight ratios of dispersed semiconductor CuS (0–5 wt.%) have been prepared and characterized. The dispersal of CuS was achieved by its in situ formation in the viscous solution of polymer electrolyte (PEO:NH₄ClO₄) by sulfuration of CuSO₄ using H₂S. The band gap of CuS dispersed in the composites was found to be ~2.4 eV, which is higher than that of the bulk CuS for which it is 2.2 eV. Scanning electron microscopy studies show that the particle size varies from ~200 nm to several hundreds of nanometers. Polarization studies show that the semiconductor dispersed polymer composite so obtained has mixed ionic and electronic conduction. Detailed I–V studies show that the dispersoid is a p-type semiconductor.     

Dipolar S=O...C=O and C—H...O interactions in the molecular organization of 4,6‐di‐O‐acetyl‐2‐O‐tosyl‐myo‐inositol 1,3,5‐orthoesters

In the absence of conventional hydrogen bonding, the molecules of 4,6‐di‐O‐acetyl‐2‐O‐tosyl‐myo‐inositol 1,3,5‐orthoformate, C₁₈H₂₀O₁₀S, (I), and 4,6‐di‐O‐acetyl‐2‐O‐tosyl‐myo‐inositol 1,3,5‐orthobenzoate, C₂₄H₂₄O₁₀S, (II), are associated via C—H...O interactions. Molecules of (II) are additionally linked via dipolar S=O...C=O contacts. It is interesting to note that the sulfonyl O atom involved in the dipolar S=O...C=O contacts does not take part in any other interaction, indicating the competitive nature of this contact relative to the weak hydrogen‐bonding interactions.     

Tertiary phosphine-appended transition metal ferrocenyl dithiocarbamates: Syntheses,Hirshfeld surface,and electrochemical analyses

Five new heteroleptic complexes of Cu(I), Ag(I), and Ni(II) having formulae [Cu₃(dtc)₂(dppf)₂]PF₆ ( Cu-I ), [Cu₃(dtc)₂(dppe)₂]PF₆ ( Cu-II ), [Cu(PPh₃)₂(dtc)] ( Cu-III ), [Ag₃(dtc)₂(PPh₃)₂]NO₃ ( Ag-I ), and [Ni(dtc)(dppf)]PF₆ ( Ni-I ) (dtc = N-ethanol-N-methylferrocenyl-dithiocarbamate; dppf = 1,1′-bis(diphenylphosphino)ferrocene; dppe = 1,1′-bis(diphenylphosphino)ethane; PPh₃ = tripheylphosphine) have been synthesized and characterized using elemental analysis, Fourier-transform infrared, multinuclear nuclear magnetic resonance, UV–Vis spectroscopy, and single-crystal X-ray diffraction. The single-crystal X-ray diffraction studies indicate that Ag-I forms a rare trinuclear cluster in which the geometry around the two silver centers Ag1 and Ag3 is distorted tetrahedral, whereas the third silver center Ag2 shows a distorted trigonal planar geometry. The Ni-I complex has a distorted square-planar geometry around the Ni center. In addition, a side product [Ag₂{S₂(dppf)₂}] ( Ag-II ) was obtained during an attempt to synthesize [Ag(dppf)(dtc)], where the two Ag centers are bridged by two sulfido centers and coordinated with two phosphorus centers of the dppf ligand to give rise to a distorted tetrahedral geometry. The solid-state structures of Ag-I , Ni-I , and Ag-II are stabilized by a variety of weak interactions. The nature of these interactions has been addressed with the help of Hirshfeld surface analyses. In addition, the weak argentophilic interaction in Ag-I and Ag-II have been studied using quantum theory of atoms in molecules and natural bond orbital calculations. The electrochemical properties of the complexes have been investigated using cyclic voltammetry, where Cu-I and Cu-II exhibited two quasi-reversible waves, whereas Cu-III , Ag-I , Ag-II , and Ni-I exhibited only one quasi-reversible peak.     

Some numerical techniques for solving elliptic interface problems

Many physical phenomena can be modeled by partial differential equations with singularities and interfaces. The standard finite difference and finite element methods may not be successful in giving satisfactory numerical results for such problems. Hence, many new methods have been developed. Some of them are developed with the modifications in the standard methods, so that they can deal with the discontinuities and the singularities. In this article, a survey has been done on some recent efficient techniques to solve elliptic interface problems. © 2010 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 28: 94‐114, 2012