Color tuning of Y3Al5O12:Ce phosphor and their blend for white LEDs

Gadolinium or lanthanum co-doped (0.5 mole) yttrium aluminum garnet doped with cerium phosphors were synthesized by a citric acid gel method and the effect of co-dopants on the structural and luminescent properties were studied. A significant peak shift in the photoluminescence spectra of yttrium aluminum garnet doped cerium was observed from 535 to 556 and 576 nm for gadolinium or lanthanum co-doped phosphors, respectively. The color tuned phosphor were blended with yttrium aluminum garnet doped cerium which showed a considerable improvement in the Commission International De Eclairage chromaticity co-ordinate values of gallium nitride based blue light emitting diode pumped white light. White light emitted from yttrium aluminum garnet doped cerium shows a Commission International De Eclairage value of (0.229, 0.182) whereas the yttrium aluminum garnet doped cerium phosphor blended with gadolinium or lanthanum co-doped phosphor shows (0.262, 0.243) and (0.295, 0.282), respectively. These results demonstrate the possibility to use these phosphor blends to enhance the white light generation in the field of white-light emitting diode solid-state lighting.     

Enhanced mobility of confined polymers

Non-classical behaviour, brought about by a confinement that imposes spatial constraints on molecules, is opening avenues to novel applications. For example, carbon nanotubes, which show rapid and selective transport of small molecules across the nanotubes, have significant potential as biological or chemical separation materials for organic solvents or gaseous molecules. With polymers, when the dimensions of a confining volume are much less than the radius of gyration, a quantitative understanding of perturbations to chain dynamics due to geometric constraints remains a challenge and, with the development of nanofabrication processes, the dynamics of confined polymers have significant technological implications. Here, we describe a weak molecular-weight-dependent mobility of polymers confined within nanoscopic cylindrical pores having diameters smaller than the dimension of the chains in the bulk. On the basis of the chain configuration along the pore axis, the measured mobility of polymers in the confined geometry is much higher than the mobility of the unconfined chain. With the emergence of nanofabrication processes based on polymer flow, the unexpected enhancement in flow and reduction in intermolecular entanglements are of significant importance in the design and execution of processing strategies.     

Sequence-dependent structural effects in left-handed DNA

About 25 years ago the DNA sequence d(CGCGCG)₂ was crystallized, and the structure solved as a left-handed helix, dubbed Z-DNA. Many crystal structures of variants of this first sequence have since been obtained. In our laboratory we have focused on what happens to the helical structure, inter-helical interactions, and the solvent interactions when a single A:T (adenine–thymine) base pair replaces a G:C (guanine–cytosine) base pair in the hexameric sequence. We present here a review of these studies. The review addresses three topics. In the first part, it discusses the effect of A:T base pairs on the structure of Z-DNA. The crystal structures demonstrate that the degree of structural perturbation that an A:T base pair produces depends on its position in the sequence, as this alters the length of the G:C tract. The presence of four continuous G:C base pairs appears to be necessary and sufficient to nucleate a Z-type structure. In the second part, the review deals with interactions between helices and crystal packing modes in Z-DNA. It examines the consequences to these aspects, of the presence of an A:T base pair in the sequence. Hexameric duplexes may be approximated as cylinders. This leads to degeneracy in crystal packing modes in Z-DNA, particularly at low resolution. The presence of a single A:T base pair breaks the two-fold symmetry in the sequence and gives rise to directionality in the cylinders. This has interesting effects on the inter-helical interactions, and therefore on the crystal packing. Metal ion and solvent interactions are discussed in the third section of the review. Different ions have different modes of binding to the helices. Some of these are specific to the sequence and lead not only to subtle, but well-marked, variations in the helical structure, but also to differences in helical contacts and therefore crystal packing. In some cases they induce disorder in crystal packing. In others, the ions interact with the helices in a non-specific manner.

Sequence-dependent structural effects in left-handed DNA

All authors

S. Thiyagarajan & N. Gautham

https://doi.org/10.1080/08893110500381264

Published online:

25 January 2007

Table     

3D preform shape optimization in forging using reduced basis techniques

Three-dimensional preform shape optimization of complex forgings with a weighted summation of multiple basis shapes is presented in this article. Currently, 2D preform shape optimization is well developed; however, in cases in which the parts are neither axisymmetric nor plane strain, 2D assumptions do not hold well. The number of design variables required to define the 3D preform shape is high, making most iterative design methods impractical for shape optimization. The goal here is to make design optimization practical and efficient by developing reduced-order modeling techniques for 3D preform shape optimization. The preform shape is treated as a linear combination of various billet shapes, called basis shapes, with the weights for each basis shape used as design variables, thereby reducing the number of design variables. It is very difficult to obtain the necessary gradient information for 3D forging simulations, so a non-gradient method is used to build the surrogate model on which optimization is performed. The optimization problem is formulated to minimize strain variance while placing constraints on underfill. Representative problems are used to demonstrate the effectiveness of the approach.     

A Conformational Mimetic Approach for the Synthesis of Carbocyclic Nucleosides as Anti‐HCV Leads

Computer‐aided approaches coupled with medicinal chemistry were used to explore novel carbocyclic nucleosides as potential anti‐hepatitis C virus (HCV) agents. Conformational analyses were carried out on 6‐amino‐1H‐pyrazolo[3,4‐d]pyrimidine (6‐APP)‐based carbocyclic nucleoside analogues, which were considered as nucleoside mimetics to act as HCV RNA‐dependent RNA polymerase (RdRp) inhibitors. Structural insight gained from the modeling studies revealed the molecular basis behind these nucleoside mimetics. The rationally chosen 6‐APP analogues were prepared and evaluated for anti‐HCV activity. RdRp SiteMap analysis revealed the presence of a hydrophobic cavity near C7 of the nucleosides; introduction of bulkier substituents at this position enhanced their activity. Herein we report the identification of an iodinated compound with an EC₅₀ value of 6.6 μM as a preliminary anti‐HCV lead.     

AGGREGATION OF COMPLEXES FORMED IN THE EXTRACTION OF SELECTED METAL CATIONS BY P,P'-DI(2-ETHYLHEXYL) METHANEDIPHOSPHONIC ACID*

ABSTRACT

The aggregation of several metal complexes formed during solvent extraction with P,P'-di(2-ethylhexyl) methanediphosphonic acid, H₂DEH[MDP], in deuterated toluene, has been investigated by small angle neutron scattering (SANS). The SANS results show that the Ca(II)-, Al(ni)-, La(III)- and Nd(III)-H₂DEH[MDP] compounds exhibit little or no tendency to aggregate. Uranyl complexes of H₂DEH[MDP] at high metal loading form small aggregates with an aggregation number of approximately 14. This behavior is in sharp contrast with the Th(IV)-H₂DEH[MDP] system which forms large aggregates in the organic phase under high metal loading conditions. The aggregation behavior of the various metal-H₂DEH[MDP] compounds is discussed in light of the information obtained from earlier solvent extraction, vapor pressure osmometry, and infrared spectroscopy studies.     

SMALL ANGLE NEUTRON SCATTERING INVESTIGATION OF THE SPECIES FORMED IN THE EXTRACTION OF Sr(II) BY MIXTURES OF DI-n-OCTYLPHOSPHORIC ACID AND DICYCLOHEXANO-18-CROWN-6

ABSTRACT

Deuterated toluene solutions of di-n-octylphosphoric acid, HDOP, containing Sr⁺ extracted from 0.1 M LiNO₃ aqueous solutions, were investigated by small angle neutron scattering (SANS). The extractions were also performed in the presence of either the cis-syn-cis or the cis-anti-cis stereoisomer of dicyclohexano-18-crown-6 (DCH18C6) in combination with HDOP in the toluene phase. The addition of the crown ether increased metal extraction into the organic phase over that observed with HDOP alone (synergistic extraction), The cis-syn-cis isomer was more effective than the cis-anti-cis isomer in enhancing Sr(II) extraction in the synergistic system. The SANS results confirmed that when the metal cation is extracted by HDOP present in large stoichiometric excess, the predominant species formed in the organic phase can be described as Sr(H(DOP)₂)₂ with 2 extra HDOP molecules solvating the complex. In the synergistic crown ether-HDOP system, the SANS data are consistent with solvent extraction data suggesting the formation of complexes containing one crown ether and two HDOP dimers. In the extraction of Sr(II) by HDOP alone, the SANS data reveal the presence of small amounts of large aggregates. Both the cis-syn-cis and cis-anti-cis isomers of DCH18C6 inhibit the formation of these aggregates. The cis-anti-cis isomer, however, despite its weaker complexation of strontium, is more effective in preventing aggregate formation.     

Simultaneous reduction of NO–smoke–CO<Subscript>2</Subscript> emission in a biodiesel engine using low-carbon biofuel and exhaust after-treatment system

The present work focuses on the simultaneous reduction of NO–smoke–CO₂ emission in a Karanja oil methyl ester (KOME)-fueled single-cylinder compression ignition engine by using low-carbon biofuel with exhaust after-treatment system. Replacement of KOME for diesel reduced smoke emission by 3% but resulted in increase of NO emission and CO₂ emission by 13 and 35% at 100% load condition. In order to reduce CO₂ emission, tests were conducted with a blend of KOME and orange seed oil (OSO), a low-carbon fuel on equal volume basis (50–50). At the same operating conditions, compared to KOME, 27% reduction in CO₂ emission and 5% reduction in smoke emission were observed. However, a slight increase in NO emission was observed. To achieve simultaneous reduction of NO–smoke–CO₂ emissions, three catalysts, namely monoethanolamine, zeolite and activated carbon, were selected for exhaust after-treatment system and tested with optimum KOME–OSO blend. KOME–OSO + zeolite showed a great potential in simultaneous reduction of NO–smoke–CO₂ emissions. NO, smoke and CO₂ emissions were simultaneously reduced by about 15% for each emission compared to diesel at 100% load condition. The effect of exhaust after-treatment system with KOME–OSO blend on combustion, performance and other emission parameters is discussed in detail in this study. Fourier transform infrared spectrometry analysis and testing were done to identify the absorbance characteristics of zeolite material.     

Design and performance of EUV resist containing photoacid generator for sub-100 nm lithography

To fulfill the SIA roadmap requirements for EUV resists, the development of entirely new polymer platforms is necessary. In order to address issues like Line Edge Roughness (LER) and photospeed, we have developed a novel chemically amplified photoresist containing a photoacid generator (PAG) in the main chain of the polymer. The incorporation of a cationic PAG unit, phenyl methacrylate dimethylsulfonium nonaflate (PAG), in the resist backbone showed increased sensitivity, when compared with analogous blend PAG resist samples. In addition, the overall lithographic performance improved by using the counter anion (nonaflate) in the PAG units. The newly synthesized polymer bound PAG resist, poly (4-hydroxystyrene-co-2-ethyl-2-adamantyl methacrylate-co-PAG) showed sub-50 nm features using EUV Lithography.     

Defects Induced Magnetism in WO<Subscript>3</Subscript> and Reduced Graphene Oxide-WO<Subscript>3</Subscript> Nanocomposites

A series of reduced graphene oxide (rGO)-WO₃ nanocomposites were prepared by hydrothermal method using GO and tungsten complex. The nanocomposites were characterized by powder XRD, Raman spectroscopy, FT-IR spectroscopy, HRTEM, XPS, photoluminescence (PL), and magnetic studies. The structural analysis confirms the hexagonal crystal structure and formation of rGO-WO₃ nanocomposites. HRTEM images show rod-like shape WO₃ distributed on the wrinkle structure of rGO sheets. XPS results confirm the oxidation state and oxygen vacancies present in the samples. PL spectra of the samples show blue emission and indicate the existence of surface defects and oxygen vacancies. The M–H loop of rGO-WO₃ nanocomposites reveal that the co-existence of both ferro and antiferromagnetism at room temperature. The incorporation of rGO sheets notably increase magnetic behavior of composites due to extended C–C bond conducts much stronger coupling between the 5d and 6s orbitals of tungsten and carbon atoms.