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Shiv Nadar University

(SoNS) School of Natural Sciences

We report on the search for ferromagnetism in undoped and cobalt-doped high- k dielectric Hf O2 films. Over a broad range of growth conditions, we do not observe ferromagnetism in undoped Hf O2 films. On the other hand, we do observe room temperature ferromagnetism in dilutely Co-doped Hf O2 films, but the origin of the same appears extrinsic (a Co rich surface layer) at least for the regime of growth conditions explored. © 2006 American Institute of Physics.

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Physics

Fulltext

Applied Physics Letters

Search for ferromagnetism in undoped and cobalt-doped Hf O 2-δ

We report on the fabrication and electrical characterization of epitaxial metal-semiconductor junctions between Y1 Ba2 Cu3 O7-δ (YBCO) (optimally doped and Zn doped) and (001) Nb:SrTi O3 with different Nb concentrations (0.05%, 0.1%, and 0.5%). The current-voltage characteristics of such epitaxial junctions are nonlinear and rectifying, and these are dramatically enhanced with decreasing Nb concentration and Zn doping. Indeed, for the case of 0.05% Nb:STO, reverse breakdown voltage as high as -18 V (-28 V) is realized for optimally doped (Zn doped) YBCO. These data are analyzed within the framework of thermionic emissiondiffusion models for Schottky and metal-insulator- semiconductor-type junctions. © 2006 American Institute of Physics.

Journal of Applied Physics

Room temperature rectifying characteristics of epitaxial Y 1Ba 2Cu 3-xZn xO 7-δ (x=0.0,0.2) and Nb:SrTiO 3 (Nb: 0.05%, 0.1%, 0.5%) heterojunctions

Background: The ORF1 of hepatitis E virus (HEV) encodes a nonstructural polyprotein of ∼186 kDa that has putative domains for four enzymes: a methyltransferase, a papain-like cysteine protease, a RNA helicase and a RNA dependent RNA polymerase. In the absence of a culture system for HEV, the ORF1 expressed using bacterial and mammalian expression systems has shown an ∼186 kDa protein, but no processing of the polyprotein has been observed. Based on these observations, it was proposed that the ORF1 polyprotein does not undergo processing into functional units. We have studied ORF1 polyprotein expression and processing through a baculovirus expression vector system because of the high level expression and post-translational modification abilities of this system. Results: The baculovirus expressed ORF1 polyprotein was processed into smaller fragments that could be detected using antibodies directed against tags engineered at both ends. Processing of this ∼192 kDa tagged ORF1 polyprotein and accumulation of lower molecular weight species took place in a time-dependent manner. This processing was inhibited by E-64d, a cell-permeable cysteine protease inhibitor. MALDI-TOF analysis of a 35 kDa processed fragment revealed 9 peptide sequences that matched the HEV methyltransferase (MeT), the first putative domain of the ORF1 polyprotein. Antibodies to the MeT region also revealed an ORF1 processing pattern identical to that observed for the N-terminal tag. Conclusion: When expressed through baculovirus, the ORF1 polyprotein of HEV was processed into smaller proteins that correlated with their proposed functional domains. Though the involvement of non-cysteine protease(s) could not be be ruled out, this processing mainly depended upon a cysteine protease. © 2006 Sehgal et al; licensee BioMed Central Ltd.

Life Sciences

Virology Journal

Expression and processing of the hepatitis E virus ORF1 nonstructural polyprotein

The western margin of Australia is unique in being the only eastern boundary region undergoing no upwelling as the poleward flowing Leeuwin Current (LC) nullifies the equatorward-driven wind-induced circulation. The principal forcing mechanism of the Leeuwin Current is the alongshore pressure gradients and associated zonal geostrophic flows along the West Australian margin. Based on planktic foraminiferal census counts and stable isotopic analysis of a surface-dwelling planktic foraminifera, Globigerinoides sacculifer, we show that during the Quaternary there have been five intervals when this eastern boundary region behaved in an opposite manner and the margin experienced extensive upwelling due to weakening of the LC and dominance of equatorward wind-driven circulation, causing offshore Ekman transport. These events occurred at 2.22, 1.83, 0.68, 0.45 and 0.04 Ma and have been named here as PL-1 to PL-5 in ascending stratigraphic order. We demonstrate here that the previous two events, PL-1 and PL-2, occurred due to ENSO-induced changes in the Western Pacific Warm Pool, while the last three events, PL-3, PL-4, and PL-5, occurred due to reduced Indonesian throughflow as a result of lowered sea level caused by ice volume expansion. We envisage here that these periods must be those of reduced net heat input to the Indian Ocean from the Pacific via Indonesian Seaway and thus should have an effect on sea surface temperature of the Indian Ocean and Indian monsoon.

Current Science

Palaeoceanographic and palaeoclimatic history of ODP site 763A (Exmouth Plateau), southeast Indian Ocean: 2.2 Ma record of planktic foraminifera

Auxin exerts pleiotropic effects on plant growth and development by regulating the expression of early auxin-responsive genes of auxin/ indoleacetic acid (Aux/IAA), small auxin-up RNA, and GH3 classes. These genes have been studied extensively in dicots like soybean and Arabidopsis. We had earlier characterized a cDNA of the first monocot member of Aux/IAA family from rice. The achievement of the large scale rice genome sequencing combined with the availability of full-length cDNA sequences from Knowledge-based Oryza Molecular Biological Encyclopedia provided us the opportunity to draw up the first comprehensive list of Aux/IAA genes in a monocot. By screening the available databases, we have identified 31 Aux/IAA genes having high sequence identity within the conserved domains I, II, III, and IV. The genomic organization as well as chromosomal location of all the Oryza sativa indoleacetic acid (OsIAA) genes is reported. The rice Aux/IAA proteins can be classified in two groups (A and B) on the basis of their phylogenetic relationship with Arabidopsis Aux/IAA proteins. An evolutionary pattern of the rice Aux/IAA genes has been discussed by analyzing their structure (exon/intron organization) and duplications. Interestingly, the duplication of rice Aux/IAA genes was found to be associated with chromosomal block duplication events in rice. The in-silico analysis has been complemented with real-time polymerase chain reaction analysis to quantify transcript levels of all Aux/IAA family members. OsIAA genes showed differential and overlapping organ-specific expression patterns in light- and dark-grown seedlings/plants. Although auxin enhanced the transcript abundance of most of the OsIAA genes, the effect was more pronounced on OsIAA9, 14, 19, 20, 24, and 31. These results provide a foundation for future studies on elucidating the precise role of rice Aux/IAA genes in early steps of auxin signal transduction. © Springer-Verlag 2005.

Functional and Integrative Genomics

Structure and expression analysis of early auxin-responsive Aux/IAA gene family in rice (Oryza sativa)

The electron transfer reactions involving ascorbic acid as electron donor are in general very fast. The present work is an example of electron transfer between ascorbic acid and a (μ-oxo) diiron(III,III) complex, where the otherwise very fast process has been slowed down by the presence of large excess of chloride ion. The complex ion [Fe2III(μ-O)(phen)4(H2O)2]4+(1) (phen = 1,10-phenanthroline) and its H2O acid dissociated derivatives [Fe2III(μ-O)(phen)4(H2O)(OH)]3+(1a)and[Fe2III(μ-O)(phen)4(OH)2]2+(2a) coexist in rapid equilibria in the range pH 3.95-5.09 in presence of excess phen (pKa1 = 3.71 ± 0.11, pKa2 = 5.28 ± 0.10). The complex solution reacts with ascorbic acid in presence of excess phenanthroline to produce tris(phenanthroline)iron(II) and dehydroascorbic acid. All the three forms of the complex ion are kinetically active, whereas the ascorbate ion and not the free ascorbic acid has been found to be the reactive species. The observed rate constants exhibit a first-order dependence on the total concentration of ascorbic acid and an inverse square dependence on chloride ion concentration, while the dependence on [H+] is complex in nature. Kinetic and stoichiometric results indicate that one ascorbate ion reacts with one complex molecule in an inner sphere pathway. The kinetic experiments were carried out at 25°C in aqueous media. The ionic strengths of the reaction media were kept 1.0 M using NaNO3. © 2005 Elsevier Ltd. All rights reserved.

Chemistry

Polyhedron

Electron transfer between ascorbic acid and a (μ-oxo) diiron(III,III) complex: An example of chloride inhibition

This paper deals with the mathematical modeling of pest management under viral infection (i.e. using viral pesticide) and analysis of its essential mathematical features. As the viral infection induces host lysis which releases more virus into the environment, on the average 'κ' viruses per host, κ∈(1,∞), the 'virus replication parameter' is chosen as the main parameter on which the dynamics of the infection depends. We prove that there exists a threshold value κ0 beyond which the endemic equilibrium bifurcates from the free disease one. Still for increasing κ values, the endemic equilibrium bifurcates towards a periodic solution. We further analyse the orbital stability of the periodic orbits arising from bifurcation by applying Poor's condition. A concluding discussion with numerical simulation of the model is then presented. © 2005 Elsevier Ltd. All rights reserved.

Mathematics

Journal of Theoretical Biology

Pest control through viral disease: Mathematical modeling and analysis

Implanting photoactive ions into quartz or silica is a simple and efficient way to tune the luminescence light used for various optoelectronic applications. However, such ion implantation damages or even destroys the crystalline order in quartz. We report here on cathodoluminescence of α-quartz after 175 keV Rb-ion implantation and epitaxial growth when annealing the samples in air or 18 O 2. In the cathodoluminescence spectra taken at room temperature, five bands were identified. In addition to three intrinsic bands at 2.40, 2.79, and 4.30 eV, which are related to the quartz and/or silica matrix, two strong violet sub-bands at 3.25 and 3.65 eV were observed, which appear to be strongly correlated with the presence of alkali ions and/or the degree of epitaxy of the matrix. Their properties and origin are discussed in relation to similar bands observed after Ba, Ge, and Na ion implantation.

Applied Physics B: Lasers and Optics

Cathodoluminescence during epitaxy in Rb-ion irradiated α-quartz

Even at low fluences doping of quartz by ion implantation results in amorphization. Here we report on the measurement of cathodoluminescence and surface structures during solid phase epitaxy in Na-implanted α-quartz annealed in 18O2 atmosphere. Complete epitaxy was achieved under appropriate conditions of ion fluence, annealing temperature and time. The crystalline structure of the samples was studied by Rutherford backscattering channelling spectroscopy and the 18O-16O exchange between the matrix and 18O2 annealing gas by elastic recoil detection analysis. In the cathodoluminescence spectra taken at room temperature, five bands were identified and assigned to various defect centres. Two of the bands in the violet region at 3.25 and 3.65 eV strongly vary in intensity at 843-1173 K annealing temperature and appear to be intimately correlated with the presence of Na-ions in the implanted region of the matrix. Finally, atomic force microscopy enabled, for the first time, the observation of the correlation of surface structures and epitaxy. © 2006 Elsevier B.V. All rights reserved.

Journal of Non-Crystalline Solids

Solid phase epitaxy of Na-ion irradiated α-quartz: Cathodoluminescence, kinetics and surface morphology

It is shown that dilute niobium doping has a significant effect on the ferromagnetism and microstructure of dilutely cobalt-doped anatase TiO 2 films. Epitaxial films of anatase TiO 2 with 3% Co, without and with 1% niobium doping were grown by pulsed-laser deposition at 875°C at different oxygen pressures. For growth at 10 -5 Torr niobium doping suppresses the ferromagnetism, while it enhances the same in films grown at 10 -4 Torr. High-resolution Z-contrast scanning transmission electron microscopy and electron energy loss spectroscopy show uniform surface segregation of cobalt-rich Ti 1-x-yCo xNb yO 2-δ phase, but without cobalt metal clusters. © 2006 American Institute of Physics.