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Shiv Nadar University

(SoNS) School of Natural Sciences

The solid-phase epitaxial regrowth of Rb-irradiated α-quartz during annealing was investigated. The depth distribution of Rb atoms and the thickness of the amorphous layers calculated using Rutherford backscattering and Channeling (RBCS) spectrometry. It was observed that the chemically guided epitaxy in α-quartz demonstrated the correlations which governed the epitaxial regrowth, the Rb out-diffusion, and the oxygen exchange between the silica matrix and annealing gas. The results show that the swelling of the SiO2 matrix during implantation and recompaction during epitaxy was proven by the surface topography measurements.

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Physics

Fulltext

Journal of Applied Physics

Chemically guided epitaxy of Rb-irradiated α-quartz

Bacterial Blight (BB) caused by Xanthomonas oryzae pv. oryzae is a major disease of rice in tropical Asia. Since all the Basmati varieties are highly susceptible and the disease is prevalent in the entire Basmati growing region of India, BB is a severe constraint in Basmati rice production. The present study was undertaken with the objective of combining the important Basmati quality traits with resistance to BB by a combination of phenotypic and molecular marker-assisted selection (MAS). Screening of 13 near-isogenic lines of rice against four isolates of the pathogen from Basmati growing regions identified the Xa4, xa8, xa13 and Xa21 effective against all the isolates tested. Two or more of these genes in combination imparted enhanced resistance as expressed by reduced average lesion length in comparison to individual genes. The two-gene pyramid line IRBB55 carrying xa13 and Xa21 was found equally effective as three/four gene pyramid lines. The two BB resistance genes present in IRBB55 were combined with the Basmati quality traits of Pusa Basmati-1 (PB-1), the most popular high yielding Basmati rice variety used as recurrent parent. Phenotypic selection for disease resistance, agronomic and Basmati quality characteristics and marker-assisted selection for the two resistance genes were carried out in BC 1F 1, BC 1F 2 and BC 1F 3 generations. Background analysis using 252 polymorphic amplified fragment length polymorphism (AFLP) markers detected 80.4 to 86.7% recurrent parent alleles in BC 1F 3 selections. Recombinants having enhanced resistance to BB, Basmati quality and desirable agronomic traits were identified, which can either be directly developed into commercial varieties or used as immediate donors of BB resistance in Basmati breeding programs.

Life Sciences

Molecular Breeding

Combining bacterial blight resistance and Basmati quality characteristics by phenotypic and molecular marker-assisted selection in rice

The effect of swift-heavy-ion irradiation on a very stable and well-studied Al62Cu25.5Fe12.5 icosahedral quasicrystalline system is discussed here. The experiments are performed in the pure electronic excitation regime, where various ranges of energy (1.2 to ∼2.5 keV/Å) are systematically deposited in to the system, causing electronic excitations in them. The choice of ions was generally dependent on calculations based on Monte-Carlo simulations and some existing literature studies on metals/metallic alloys. Samples were irradiated at fluences of 1011 to a few 1013 ions/cm2, and a homogeneous irradiation was ensured. The effect of these electronic excitations on the electronic structure of the quasicrystals is analyzed by doing in situ resistivity vs. fluence and ex situ resistivity vs. temperature measurements, made on the irradiated pieces. © 2004 Published by Elsevier B.V.

Journal of Non-Crystalline Solids

Swift-heavy-ion irradiation on Al62Cu25.5Fe 12.5 quasicrystals

This article reports on the formation of iron nitrides during nitrogen ion irradiation of Fe/Si bilayers at room temperature. The 30 nm 57 Fe/Si bilayers were prepared by pulsed laser ablation and irradiated with 22 keV N 2+ ions at fluences of (0.6-2)×10 17 ions/cm 2 . The structural changes and phases formed by irradiation were analyzed by Rutherford backscattering spectroscopy (RBS), X-ray diffraction analysis (XRD) and conversion electron Mössbauer spectroscopy (CEMS). The results clearly show the formation of several iron nitrides. At the lower fluences, the samples contain a mixture of ε-Fe 2+x N and α-Fe with nitrogen interstitials. For the highest fluence, the paramagnetic ε-Fe 2 N (61%) phase predominated. It can be concluded that the elemental iron almost fully transforms to an iron-nitride layer, but that no iron silicides are formed. © 2003 Elsevier B.V. All rights reserved.

Thin Solid Films

Formation of iron-nitrides by irradiation of 57 Fe/Si bilayers with N 2+ ions

The magnetic behavior of (Al,Ge)65CuMn quasicrystalline samples with ∼22 and 24 at.% Mn was investigated. High disordered magnetism was observed for these quaternary alloys. Short-range ferromagnetism in samples with high Ge and high Mn content along with the oscillatory magnetization were also observed. A double transition at T&lt;75 K was observed in the sample with 0 at. % Ge. The results indicate that with the increase in the concentration of icosahedral phase in the alloys, magnetic disorder increases.

Magnetic behavior of (Al,Ge)65CuMn quaternary alloy quasicrystals

The doping single-crystalline α-quartz with 120 keV Ge +-ion implantation under the condition of dynamic solid phase epitaxial regrowth was discussed. The light emitting properties possibly suitable for optoelectronic devices were analyzed by measuring cathodoluminescence spectra. It was found that the Ge implantation produced amorphous layers varying in depth with temperature. Analysis shows that at a fluence of 7×10 14 Ge-ions/cm 2 and an implantation temperature of 1073 K, Ge implantation was accompanied by a strong increase in the luminescence.

Stable violet cathodoluminescence of α-quartz after Ge + implantation at elevated temperature

The CCR5 chemokine receptor has recently been found to play a crucial role in the viral entry stage of HIV infection and has therefore become an attractive potential target for anti-HIV therapeutics. On the other hand, the lack of CCR5 crystal structure data has impeded the development of structure-based CCR5 antagonist design. In this paper, we compare two three-dimensional Quantitative Structure-Activity Relationship (3D-QSAR) methods: Comparative Molecular Field Analysis (CoMFA) and Comparative Molecular Similarity Indices Analysis (CoMSIA) on a series of piperidine-based CCR5 antagonists as an alternative approach to investigate the interaction between CCR5 antagonists and their receptor. Superimposition of antagonist structures was performed using two alignment rules: atomic/centroid rms fit and rigid body field fit techniques. The 3D QSAR models were derived from a training set of 72 compounds, and were found to have predictive capability for a set of 19 holdout test compounds. The resulting contour maps produced by the best CoMFA and CoMSIA models were used to identify the structural features relevant to biological activity in this series of compounds. Further analyses of these interaction-field contour maps also showed a high level of internal consistency. © 2003 Elsevier Ltd. All rights reserved.

Chemistry

Bioorganic and Medicinal Chemistry

Three-dimensional quantitative structure-activity relationship analyses of piperidine-based CCR5 receptor antagonists

Several 6-aryloxymethyl-2,4-dimethyl-1,2,4-triazolo [3,4-b]-1,3,4- thiadiazepines II and 2-arylamino-4-aryloxymethyl-1,2,4-triazolo [3,4-b][1,3,4] thiadiazoles III have been synthesized from the synthon 3-aryloxymethyl-4-amino- 5-mercapto-1,2,4-triazoles I. The molluscicidal activity of few titled compounds have been evaluated against the snail Lymnaea acuminata. The LC50 slope, t-ratio, heterogeneity and g values have been determined and discussed.

Indian Journal of Heterocyclic Chemistry

Synthesis and molluscicidal activity of 6-aryloxymethyl-2,4-dimethyl-1,2,4- triazolo [3,4-b]-[1,3,4]-thiadiazepines and 2-arylamino-4-aryloxymethyl-1,2,4- triazolo [3,4-b] [1,3,4] thiadiazoles

Microsatellite markers were used for fingerprinting of hybrids, assessing variation within parental lines and testing the genetic purity of hybrid seed lot in rice. Ten sequence tagged microsatellite sites (STMS) markers were employed for fingerprinting 11 rice hybrids and their parental lines. Nine STMS markers were found polymorphic across the hybrids and produced unique fingerprint for the 11 hybrids. A set of four markers (RM 206, RM 216, RM 258 and RM 263) differentiated all the hybrids from each other, which can be used as referral markers for unambiguous identification and protection of these hybrids. Cluster analysis based on Jaccard's similarity coefficient using UP-GMA grouped the hybrids into three clusters. Within the cluster all the hybrids shared a common cytoplasmic male sterile line as female parent. The genetic similarity between the hybrids ranged from 0.33 to 0.92 with an average similarity index of 0.63. The analysis of plant-to-plant variation within the parental lines of the hybrid Pusa RH 10, using informative markers indicated residual heterozygosity at two marker loci. This highlights the importance of STMS markers in maintaining the genetic purity of the parental lines. The unique value of the restorer gene linked marker for testing the genetic purity of hybrid seeds is demonstrated for the first time.

Euphytica

Molecular fingerprinting of hybrids and assessment of genetic purity of hybrid seeds in rice using microsatellite markers

The low-molecular-weight (LMW) penicillin-binding protein, PBP 5, plays a dominant role in determining the uniform cell shape of Escherichia coli. However, the physiological functions of six other LMW PBPs are unknown, even though the existence and enzymatic activities of four of these were established three decades ago. By applying fluorescence-activated cell sorting (FACS) to quantify the cellular dimensions of multiple PBP mutants, we found that the endopeptidases PBP 4 and PBP 7 also influence cell shape in concert with PBP 5. This is the first reported biological function for these two proteins. In addition, the combined loss of three DD-carboxypeptidases, PBPs 5 and 6 and DacD, also impaired cell shape. In contrast to previous reports based on visual inspection alone, FACS analysis revealed aberrant morphology in a mutant lacking only PBP 5, a phenotype not shared by any other strain lacking a single LMW PBP. PBP 5 removes the terminal D-alanine from pentapeptide side chains of muropeptide subunits, and pentapeptides act as donors for cross-linking adjacent side chains. As endopeptidases, PBPs 4 and 7 cleave cross-links in the cell wall. Therefore, overall cell shape may be determined by the existence or location of a specific type of peptide cross-link, with PBP 5 activity influencing how many cross-links are made and PBPs 4 and 7 acting as editing enzymes to remove inappropriate cross-links.