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Shiv Nadar University

(SoNS) School of Natural Sciences

The simplest purely imaginary and piecewise constant PT-symmetric potential located inside a larger box is studied. Unless its strength exceeds a certain critical value, all the spectrum of its bound states remains real and discrete. We interpret such a model as an initial element of the generalized non-Hermitian Witten's hierarchy of solvable Hamiltonians and construct its first supersymmetric partner in closed form. © World Scientific Publishing Company.

Physics

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International Journal of Modern Physics A

PT-symmetric supersymmetry in a solvable short-range model

Thin films of Nb-doped SrTiO 3 (NSTO) are grown via pulsed laser deposition (PLD) on LaAlO 3 (LAO,001), Mg Al 2O 4 (MAO,001), SrTiO 3 (STO,001), and Y-stabilized ZrO 2 (YSZ,001) substrates. The effects of the film-substrate lattice mismatch, film thickness, and substrate temperature during growth on the film properties are investigated. The electrical transport in NSTO films is shown to exhibit a strong sensitivity to strain, which is suggested to arise from the dependence of carrier mobility on bond distortions/stretching and related changes in phonon modes. © 2006 American Institute of Physics.

Applied Physics Letters

Substrate-induced strain effects on the transport properties of pulsed laser-deposited Nb-doped SrTiO 3 films

Thin films of (0.5%, 1%) Nb:SrTiO 3 dilutely doped with (2 at. %) magnetic transition elements (Cr, Co, Fe, Mn) are examined for ferromagnetism. X-ray diffraction, Rutherford backscattering ion channeling, scanning transmission electron microscopy Z-contrast imaging, and electron energy loss spectroscopy techniques establish high crystalline quality of the films with no impurity phase(s) and highly uniform dopant distribution. Although the film conductivity improves dramatically by Nb doping, no ferromagnetism is found in any of our samples over the temperature range of 365 down to 5 K. This is contrasted to the case of ferromagnetism reported in cobalt doped (La, Sr)TiO 3. © 2006 American Institute of Physics.

Search for ferromagnetism in conductive Nb:SrTiO 3 with magnetic transition element (Cr, Co, Fe, Mn) dopants

In an attempt to investigate the putative S-H⋯N hydrogen bond, we have studied the title compound, 1-formyl-3-thiosemicarbazide, which was revealed in a CSD search as a crystal structure which might show such an interaction. However, a redetermination of the structure at room temperature and careful analysis showed that the earlier study [Saxena et al (1991). Acta Cryst. C47, 2374-2376] on which the CSD search was based was in error and that the possibility of an S-H⋯N hydrogen bond is negated. The presence of five other varieties of hydrogen bond (N-H⋯O, N-H⋯S, N-H⋯N, C-H⋯O, C-H⋯S) in the crystal packing prompted us to redirect our efforts and to undertake a study of the charge-density distribution at 90 K. The topological analysis of these five varieties of hydrogen bond was carried out with Bader's quantum theory of 'atoms in molecules' and by applying Koch-Popelier's criteria. The analysis reveals that the hydrogen-bond strength is highest for N-H⋯O and lowest for C-H⋯S with N-H⋯S, N-H⋯N and C-H⋯O forming the middle order. © 2006 International Union of Crystallography Printed in Great Britain - all rights reserved.

Chemistry

Acta Crystallographica Section B: Structural Science

Five varieties of hydrogen bond in 1-formyl-3-thiosemicarbazide: An electron density study

The topological features of the charge densities, ρ(r), of three bioactive molecules, 2-thiouracil [2,3-dihydro-2-thioxopyrimidin-4(1H)-one], cytosine [4-aminopyrimidin-2(1H)-one] monohydrate and salicylic acid (2-hydroxybenzoic acid), have been determined from high-resolution X-ray diffraction data at 90 K. The corresponding results are compared with the periodic theoretical calculations, based on theoretical structure factors, performed using DFT (density-functional theory) at the B3LYP/6-31G** level. The molecules pack in the crystal lattices via weak intermolecular interactions as well as strong hydrogen bonds. All the chemical bonds, including the intra- and intermolecular interactions in all three compounds, have been quantitatively described by topological analysis based on Bader's quantum theory of 'Atoms In Molecules'. The roles of interactions such as C-H⋯O, C-H⋯S, C-H⋯π and π⋯π have been investigated quantitatively in the presence of strong hydrogen bonds such as O-H⋯O, N-H⋯O and N-H⋯S, based on the criteria proposed by Koch and Popelier to characterize hydrogen bonds and van der Waals interactions. The features of weak intermolecular interactions, such as S⋯S in 2-thiouracil, the hydrogen bonds generated from the water molecule in cytosine monohydrate and the formation of the dimer via strong hydrogen bonds in salicylic acid, are highlighted on a quantum basis. Three-dimensional electrostatic potentials over the molecular surfaces emphasize the preferable binding sites in the structure and the interaction features of the atoms in the molecules, which are crucial for drug-receptor recognition. © 2006 International Union of Crystallography Printed in Great Britain - all rights reserved.

Intra- and intermolecular interactions in small bioactive molecules: Cooperative features from experimental and theoretical charge-density analysis

We have developed a novel structure-based chemoinformatics approach to search for Complimentary Ligands Based on Receptor Information (CoLiBRI). CoLiBRI is based on the representation of both receptor binding sites and their respective ligands in a space of universal chemical descriptors. The binding site atoms involved in the interaction with ligands are identified by the means of a computational geometry technique known as Delaunay tessellation as applied to X-ray characterized ligand-receptor complexes. TAE/RECON multiple chemical descriptors are calculated independently for each ligand as well as for its active site atoms. The representation of both ligands and active sites using chemical descriptors allows the application of well-known chemometric techniques in order to correlate chemical similarities between active sites and their respective ligands. We have established a protocol to map patterns of nearest neighbor active site vectors in a multidimensional TAE/RECON space onto those of their complementary ligands and vice versa. This protocol affords the prediction of a virtual complementary ligand vector in the ligand chemical space from the position of a known active site vector. This prediction is followed by chemical similarity calculations between this virtual ligand vector and those calculated for molecules in a chemical database to identify real compounds most similar to the virtual ligand. Consequently, the knowledge of the receptor active site structure affords straightforward and efficient identification of its complementary ligands in large databases of chemical compounds using rapid chemical similarity searches. Conversely, starting from the ligand chemical structure, one may identify possible complementary receptor cavities as well. We have applied the CoLiBRI approach to a data set of 800 X-ray characterized ligand-receptor complexes in the PDBbind database. Using a k nearest neighbor (kNN) pattern recognition approach and variable selection, we have shown that knowledge of the active site structure affords identification of its complimentary ligand among the top 1% of a large chemical database in over 90% of all test active sites when a binding site of the same protein family was present in the training set. In the case where test receptors are highly dissimilar and not present among the receptor families in the training set, the prediction accuracy is decreased; however, CoLiBRI was still able to quickly eliminate 75% of the chemical database as improbable ligands. CoLiBRI affords rapid prefiltering of a large chemical database to eliminate compounds that have little chance of binding to a receptor active site. © 2006 American Chemical Society.

Journal of Chemical Information and Modeling

Chemometric analysis of ligand receptor Complementarity: Identifying Complementary Ligands Based on Receptor Information (CoLiBRI)

Aim: To evaluate the in vitro anti-HBV activity of recombinant human IFN-γ, alone and in combination with lamivudine. Methods: A recombinant baculovirus-HBV/HepG2 culture system was developed which could support productive HBV infection in vitro. Expression of HBsAg and HBeAg in infected HepG2 culture medium was detected by commercial enzyme immunoassays. HBV DNA replication intermediates were detected in infected cells by Southern hybridization and viral DNA load was determined by dot hybridization. Results: IFN-γ at 0.1 to 5 μg/L efficiently down regulated HBsAg expression in transduced HepG2 cells. At 5 μg/L, IFN-γ also suppressed HBV DNA replication in these cells. While treatment with a combination of lamivudine and IFN-γ showed no additive effect, sequential treatment first with lamivudine and then IFN-γ was found to be promising. In this culture system the best HBV suppression was observed with a pulse of 2 μmol/L lamivudine for two days, followed by 1 μg/L IFN-γ for another four days. Compared to treatment with lamivudine alone, the sequential use of 0.2 μmol/L lamivudine for two days, followed by 5 μg/L IFN-γ for six days showed a 72% reduction in HBV cccDNA pool. Conclusion: This in vitro study warrants further evaluation of a combination of IFN-γ and lamivudine, especially in IFN-α non-responder chronic hepatitis B patients. A reduced duration of lamivudine treatment would also restrict the emergence of drug-resistant HBV mutants. © 2006 The WIG Press. All rights reserved.

Life Sciences

World Journal of Gastroenterology

Inhibition of hepatitis B virus DNA replicative intermediate forms by recombinant interferon-γ

We formulate a systematic algorithm for constructing a whole class of Hermitian position-dependent-mass Hamiltonians which, to lowest order of perturbation theory, allow a description in terms of -symmetric Hamiltonians. The method is applied to the Hermitian analogue of the -symmetric cubic anharmonic oscillator. A new example is provided by a Hamiltonian (approximately) equivalent to a -symmetric extension of the one-parameter trigonometric Pöschl-Teller potential. © 2006 IOP Publishing Ltd.

Journal of Physics A: Mathematical and General

Pseudo-Hermitian versus Hermitian position-dependent-mass Hamiltonians in a perturbative framework

Physical Review-Section B-Condensed Matter

Electronic structure: Wide-band, narrow-band, and strongly correlated systems-Ab initio real-space Hartree-Fock and correlated approach to optical dielectric constants of crystalline insulators (4