Science.gov

Sample records for polymeric tetrahedral anions

  1. Polymerization of anionic wormlike micelles.

    PubMed

    Zhu, Zhiyuan; González, Yamaira I; Xu, Hangxun; Kaler, Eric W; Liu, Shiyong

    2006-01-31

    Polymerizable anionic wormlike micelles are obtained upon mixing the hydrotropic salt p-toluidine hydrochloride (PTHC) with the reactive anionic surfactant sodium 4-(8-methacryloyloxyoctyl)oxybenzene sulfonate (MOBS). Polymerization captures the cross-sectional radius of the micelles (approximately 2 nm), induces micellar growth, and leads to the formation of a stable single-phase dispersion of wormlike micellar polymers. The unpolymerized and polymerized micelles were characterized using static and dynamic laser light scattering, small-angle neutron scattering, 1H NMR, and stopped-flow light scattering. Stopped-flow light scattering was also used to measure the average lifetime of the unpolymerized wormlike micelles. A comparison of the average lifetime of unpolymerized wormlike micelles with the surfactant monomer propagation rate was used to elucidate the mechanism of polymerization. There is a significant correlation between the ratio of the average lifetime to the monomer propagation rate and the average aggregation number of the polymerized wormlike micelles.

  2. Living anionic polymerization using a microfluidic reactor

    SciTech Connect

    Iida, Kazunori; Chastek, Thomas Q.; Beers, Kathryn L.; Cavicchi, Kevin A.; Chun, Jaehun; Fasolka, Michael J.

    2009-02-01

    Living anionic polymerizations were conducted within aluminum-polyimide microfluidic devices. Polymerizations of styrene in cyclohexane were carried out at various conditions, including elevated temperature (60 °C) and high monomer concentration (42%, by volume). The reactions were safely maintained at a controlled temperature at all points in the reactor. Conducting these reactions in a batch reactor results in uncontrolled heat generation with potentially dangerous rises in pressure. Moreover, the microfluidic nature of these devices allows for flexible 2D designing of the flow channel. Four flow designs were examined (straight, periodically pinched, obtuse zigzag, and acute zigzag channels). The ability to use the channel pattern to increase the level of mixing throughout the reactor was evaluated. When moderately high molecular mass polymers with increased viscosity were made, the patterned channels produced polymers with narrower PDI, indicating that passive mixing arising from the channel design is improving the reaction conditions.

  3. Living anionic polymerization using a microfluidic reactor.

    PubMed

    Iida, Kazunori; Chastek, Thomas Q; Beers, Kathryn L; Cavicchi, Kevin A; Chun, Jaehun; Fasolka, Michael J

    2009-01-21

    Living anionic polymerizations were conducted within aluminum-polyimide microfluidic devices. Polymerizations of styrene in cyclohexane were carried out at various conditions, including elevated temperature (60 degrees C) and high monomer concentration (42%, by volume). The reactions were safely maintained at a controlled temperature at all points in the reactor. Conducting these reactions in a batch reactor results in uncontrolled heat generation with potentially dangerous rises in pressure. Moreover, the microfluidic nature of these devices allows for flexible 2D designing of the flow channel. Four flow designs were examined (straight, periodically pinched, obtuse zigzag, and acute zigzag channels). The ability to use the channel pattern to increase the level of mixing throughout the reactor was evaluated. When moderately high molecular mass polymers with increased viscosity were made, the patterned channels produced polymers with narrower PDI, indicating that passive mixing arising from the channel design is improving the reaction conditions.

  4. Efficient Removal of Anionic Radioactive Pollutant from Water Using Ordered Urea-Functionalized Mesoporous Polymeric Nanoparticle.

    PubMed

    Shen, Jian; Chai, Wei; Wang, Kaixuan; Zhang, Fang

    2017-07-12

    A urea-functionalized ordered mesoporous polymeric nanoparticle for removing the perrhenate anion ReO4(-) as the surrogate of the particularly intractable anion radioactive pollutant TcO4(-) was demonstrated in the present study. This nanomaterial (denoted as urea-MPN) was produced for the first time by a surfactant-directed urea-phenol-formaldehyde resol oligomers self-assembly protocol under hydrothermal condition. The obtained urea-MPN possessed the uniform nanosized spherical morphology with a 3D interconnected ordered cubic mesoporous structure. Also, the urea functional groups were succefully embedded in the polymer framework without the alteration of the molecular configuration. Meanwhile, it exhibited excellent β radiation resistance up to 200 kGy dose. We employed the perrhenate anion ReO4(-) to test its potential for the removal of anionic radioactive pollutant TcO4(-) from water. Interestingly, the optimized urea-MPN nanocomposite achieved the high removal efficiency at a low concentration of 0.25 mM within a short contact time of 30 min. The control experimental results revealed that the short nanoscale pore channels and the hydrophobic mesopore surface facilitated the hydrogen-bonding interaction between the charge-diffuse ReO4(-) tetrahedral oxoanion and the urea moieties in the framework of urea-MPN, accounting for the rapid and effective removal performance in pure water. Importantly, it can selectively capture ReO4(-) in the presence of different competitive anions including NO3(-), CO3(2-), SO4(2-), and PO4(3-). This attractive capability of this unique nanosized mesoporous polymeric sorbent will pave the way for the diverse applications in the decontamination of nuclear wastes in a more economical and sustainable manner.

  5. Superweak complexes of tetrahedral P4 molecules with the silver cation of weakly coordinating anions.

    PubMed

    Krossing, Ingo; van, Wüllen Leo

    2002-02-02

    The silver aluminates AgAl[OC(CF3)2(R)]4 (R = H, CH3, CF3) react with solutions of white phosphorus P4 to give complexes that bind one or two almost undistorted tetrahedral P4 molecules in an fashion: [Ag(P4)2]+[Al(OC(CF3)3)4]+ (1) containing the first homoleptic metal-phosphorus cation, the molecular species (P4)AgAl[OC(CH3)(CF3)2]4 (2), and the dimeric Ag(mu,eta2-P4)Ag bridged [(P4)AgAl[OC(H)(CF3)2]4]2 (3). Compounds 1-3 were characterized by variable-temperature (VT) 31P NMR spectroscopy (1 also by VT 32P MAS-NMR spectroscopy), Raman spectroscopy, and single-crystal X-ray crystallography. Other Ag:P4 ratios did not lead to new species, and this observation was rationalized on thermodynamic grounds. The Ag(P4)2+ ion has an almost planar coordination environment around the Ag+ ion due to d(x2 - y2)(Ag) --> sigma*(P-P) backbonding. Calculations (HF-DFT) on six Ag(P4)2+ isomers 4a-f showed that the planar eta2 form 4a is only slightly favored by 5.2 kJ mol(-1) over the tetrahedral eta2 species 4b; eta1-P4 and eta3-P4 complexes are less favorable (27-76 kJ mol(-1)). The bonding of the P4 moiety in [RhCl(eta2-P4)(PPh3)2], the only compound in which an eta2 bonding mode of a tetrahedral P4 molecule has been claimed, must be regarded as a tetraphosphabicyclobutane, and not as a tetrahedro-P4 complex, on the basis of the published NMR and vibrational spectra, the calculated geometry of [RhCl(P4)(PH3)2] (10), the highly endothermic (385 kJ mol(-1)) calculated dissociation enthalpy of 10 into P4 and RhCl(PH3)2 (11), as well as atoms in molecules (AIM) and natural bond orbital (NBO) population analyses of 10 and the Ag(P4)2+ ion. Therefore, 1-3 are the first examples of species containing eta2-coordinated tetrahedral P4 molecules.

  6. Discrete and infinite 1D, 2D/3D cage frameworks with inclusion of anionic species and anion-exchange reactions of Ag3L2 type receptor with tetrahedral and octahedral anions.

    PubMed

    Liu, Hong-Ke; Huang, Xiaohua; Lu, Tianhong; Wang, Xiujian; Sun, Wei-Yin; Kang, Bei-Sheng

    2008-06-28

    Complexes [PF6 subset(Ag3(titmb)2](PF6)2 (8) and {SbF6 subset[Ag3(titmb)2](SbF6)2}.H2O.1.5 CH3OH (9) are obtained by reaction of titmb and Ag+ salts with different anions (PF6(-) and SbF6(-)), and crystal structures reveal that they are both M3L2 cage complexes with short Ag...F interactions between the silver atoms and the fluorine atoms of the anions. In complex 8, a novel cage dimer is formed by weak Ag...F contacts; an unique cage tetramer formed via Ag...pi interactions (Ag...eta5-imidazole) between dimers and an infinite 1D cage chain is presented. However, each of the external non-disordered SbF6(-) anions connect with six cage 9s via Ag...F contacts, and each cage 9 in turn connects with three SbF6(-) anions to form a 2D network cage layer; and the layers are connected by pi-pi interactions to form a 3D network. The anion-exchange reactions of four Ag3L2 type complexes ([BF4 subset(Ag3(titmb)2](BF4)2 (6), [ClO4 subset(Ag3(titmb)2](ClO4)2 (7b), [PF6 subset(Ag3(titmb)2](PF6)2 (8) and [SbF6 subset(Ag3(titmb)2](SbF6)2.1.5CH3OH (9)) with tetrahedral and octahedral anions (ClO4(-), BF4(-), PF6(-) and SbF6(-)) are also reported. The anion-exchange experiments demonstrate that the anion selective order is SbF6(-) > PF6(-) > BF4(-), ClO4(-), and this anion receptor is preferred to trap octahedral and tetrahedral anions rather than linear or triangle anions; SbF6(-) is the biggest and most preferable one, so far. The dimensions of cage complexes with or without internal anions, anion-exchange reactions, cage assembly and anion inclusions, silver(I) coordination environments, Ag-F and Ag-pi interactions of Ag3L2 complexes 1-9 are discussed.

  7. Anion Conducting Polymeric Materials For Use in Electrolytic Salt Splitters

    NASA Astrophysics Data System (ADS)

    Newman, David; Renock, Devon

    1998-10-01

    Anion Conducting Polymeric Materials for use in Electrolytic Salt Splitters Devon Renock and David S. Newman Department of Chemistry Bowling Green State University Bowling Green, OH 43403 An anion conducting form of Flemion was produced by attaching a benzo-crown ether to the Flemion backbone and then complexing the crown ether containing material with an alkali metal ion. The alkali metal ion became trapped in the crown forming a positively charged pendent group hanging from the Teflon-like fluorocarbon chain. This positively charged moiety allows negatively charged ions to pass through readily, but prevents positively charged ions prom passing through the material. Materials with Dibenzo-18-cr-6 complexed with Potassium ion, Benzo-18-cr-6 complexed with potassium ion, and benzo-15-cr-5 complexed with sodium ion were all used successfully.

  8. Rubidium uranyl phosphates and arsenates with polymeric tetrahedral anions: Syntheses and structures of Rb{sub 4}[(UO{sub 2}){sub 6}(P{sub 2}O{sub 7}){sub 4}(H{sub 2}O)], Rb{sub 2}[(UO{sub 2}){sub 3}(P{sub 2}O{sub 7})(P{sub 4}O{sub 12})] and Rb[(UO{sub 2}){sub 2}(As{sub 3}O{sub 10})

    SciTech Connect

    Alekseev, Evgeny V.; Krivovichev, Sergey V.; Depmeier, Wulf

    2009-08-15

    The three new framework Rb uranyl phosphates and arsenates with anionic parts based on different type of polymeric anions have been prepared by high-temperature solid-state reactions: Rb{sub 4}[(UO{sub 2}){sub 6}(P{sub 2}O{sub 7}){sub 4}(H{sub 2}O)] (1), Rb{sub 2}[(UO{sub 2}){sub 3}(P{sub 2}O{sub 7})(P{sub 4}O{sub 12})] (2), Rb[(UO{sub 2}){sub 2}(As{sub 3}O{sub 10})] (3). The crystal structures of the synthesized compounds have been solved by direct methods: 1-monoclinic P2{sub 1}/c, a=9.672(1) A, b=12.951(1) A, c=32.231(3) A, beta=90.116(4){sup o}, V=4037.3(6) A{sup 3}, Z=4, R{sub 1}=0.0926 for 6351 unique reflections with |F{sub 0}|>=4sigma{sub F}; 2-monoclinic, P2{sub 1}/c, a=6.791(1) A, b=16.155(3) A, c=19.856(4) A, beta=97.48(5){sup o}, V=2159.8(7) A{sup 3}, Z=4, R{sub 1}=0.0286 for 3617 unique reflections with |F{sub 0}|>=4sigma{sub F}; 3-orthorhombic, Pbcn, a=10.558(1) A, b=11.037(1) A, c=11.464(1) A, V=1335.9(2) A{sup 3}, Z=4, R{sub 1}=0.0489 for 1384 unique reflections with |F{sub 0}|>=4sigma{sub F}. The structures of title are compounds based on 3D negatively charged frameworks with chemical compositions [(UO{sub 2}){sub 6}(P{sub 2}O{sub 7}){sub 4}(H{sub 2}O)]{sup 4-} in 1, [(UO{sub 2}){sub 3}(P{sub 2}O{sub 7})(P{sub 4}O{sub 12})]{sup 2-} in 2 and [(UO{sub 2}){sub 2}(As{sub 3}O{sub 10})]{sup -} in 3. These negative charges are compensated by rubidium cations which are in the channels of 1 and closed cages in structures of 2 and 3. The channels in 1 are directed along the a direction and have minimum dimensions approx5 Ax6 A. This is the first example of porosity generation through solid state synthesis in uranyl compounds. For the first time in uranium chemistry polymeric anionic groups P{sub 4}O{sub 12} and As{sub 3}O{sub 10} were observed in structure of 2 and 3. - Graphical abstract: The polyhedral (a) and topological (b) representation of the Rb{sub 4}[(UO{sub 2}){sub 6}(P{sub 2}O{sub 7}){sub 4}(H{sub 2}O)] crystal structure.

  9. Individually addressable thermo- and redox-responsive block copolymers by combining anionic polymerization and RAFT protocols.

    PubMed

    Schmidt, Bernhard V K J; Elbert, Johannes; Barner-Kowollik, Christopher; Gallei, Markus

    2014-04-01

    A novel diblock copolymer consisting of poly(vinylferrocene) (PVFc) and poly(N,N-diethylacrylamide) (PDEA) is synthesized via a combination of anionic and RAFT polymerization. The use of a novel route to hydroxyl-end-functionalized metallopolymers in anionic polymerization and subsequent esterification with a RAFT agent leads to a PVFc macro-CTA (M¯n = 3800 g mol(-1) ; Đ = 1.17). RAFT polymerization with DEA affords block copolymers as evidenced by (1) H NMR spectroscopy as well as size exclusion chromatography (6400 ≤ M¯n≤ 33700 g mol(-1) ; 1.31 ≤ Đ 1.28). Self-assembly of the amphiphilic block copolymers in aqueous solution leads to micelles as shown via TEM. Importantly, the distinct thermo-responsive and redox-responsive character of the blocks is probed via dynamic light scattering and found to be individually and repeatedly addressable.

  10. Enhanced Polymer Grafting from Multiwalled Carbon Nanotubes through Living Anionic Surface-Initiated Polymerization.

    SciTech Connect

    Sakellariou, Georgios; Ji, Haining; Mays, Jimmy; Baskaran, Durairaj

    2008-01-01

    Anionic surface-initiated polymerization of ethylene oxide and styrene has been performed using multiwalled carbon nanotubes (MWNTs) functionalized with anionic initiators. The surface of MWNTs was modified via covalent attachment of precursor anions such as 4-hydroxyethyl benzocyclobutene (BCBEO) and 1-benzocyclobutene-1 -phenylethylene (BCB-PE) through Diels-Alder cycloaddition at 235 C. Surface-functionalized MWNTs-g-(BCB-EO)n and MWNTs-g-(BCB-PE)n with 23 and 54 wt % precursor initiators, respectively, were used for the polymerizations. Alkoxide anion on the surface of MWNTs-g-(BCB-EO)n was generated through reaction with potassium triphenylmethane for the polymerization of ethylene oxide in tetrahydrofuran and phenyl substituted alkyllithium was generated from the surface of MWNTs-g-(BCB-PE)n using sec-butyllithium for the polymerization of styrene in benzene. In both cases, the initiation was found to be very slow because of the heterogeneous reaction medium. However, the MWNTs gradually dispersed in the reaction medium during the polymerization. A pale green color was noticed in the case of ethylene oxide polymerization and the color of initiator as well as the propagating anions was not discernible visually in styrene polymerization. Polymer grafted nanocomposites, MWNTs-g-(BCB-PEO)n and MWNTs-g-(BCB-PS)n containing a very high percentage of hairy polymer with a small fraction of MWNTs (<1 wt %) were obtained. The conversion of ethylene oxide and the weight percent of PEO on the surface of the MWNTs increased with increasing reaction time indicating a controlled polymerization. The polymer-grafted MWNTs were characterized using FTIR, 1H NMR, Raman spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and transmission electron microscopy (TEM). Size exclusion chromatography of the polymer grafted MWNTs revealed broad molecular weight distributions (1.3 < Mw/Mn < 1.8) indicating the presence of different sizes of polymer nanocomposites

  11. Poly(1-adamantyl acrylate): Living Anionic Polymerization, Block Copolymerization, and Thermal Properties

    SciTech Connect

    Lu, Wei; Huang, Caili; Hong, Kunlun; Kang, Nam-Goo; Mays, Jimmy W.

    2016-12-06

    Living anionic polymerization of acrylates is challenging due to intrinsic side reactions including backbiting reactions of propagating enolate anions and aggregation of active chain ends. In this study, the controlled synthesis of poly(1-adamatyl acrylate) (PAdA) was performed successfully for the first time via living anionic polymerization through investigation of the initiation systems of sec-butyllithium/diphenylethylene/lithium chloride (sec-BuLi/DPE/LiCl), diphenylmethylpotassium/diethylzinc (DPMK/Et2Zn), and sodium naphthalenide/dipenylethylene/diethylzinc (Na-Naph/DPE/Et2Zn) in tetrahydrofuran at -78 °C using custom glass-blowing and high-vacuum techniques. PAdA synthesized via anionic polymerization using DPMK with a large excess (more than 40-fold to DPMK) of Et2Zn as the ligand exhibited predicted molecular weights from 4.3 to 71.8 kg/mol and polydispersity indices of around 1.10. In addition, the produced PAdAs exhibit a low level of isotactic content (mm triads of 2.1%). The block copolymers of AdA and methyl methacrylate (MMA) were obtained by sequential anionic polymerization, and the distinct living property of PAdA over other acrylates was demonstrated based on the observation that the resulting PAdA-b-PMMA block copolymers were formed with no residual PAdA homopolymer. The PAdA homopolymers exhibit a very high glass transition temperature (133 °C) and outstanding thermal stability (Td: 376 °C) as compared to other acrylic polymers such as poly(tert-butyl acrylate) and poly(methyl acrylate). These merits make PAdA a promising candidate for acrylic-based thermoplastic elastomers with high upper service temperature and enhanced mechanical strength.

  12. Poly(1-adamantyl acrylate): Living Anionic Polymerization, Block Copolymerization, and Thermal Properties

    DOE PAGES

    Lu, Wei; Huang, Caili; Hong, Kunlun; ...

    2016-12-06

    Living anionic polymerization of acrylates is challenging due to intrinsic side reactions including backbiting reactions of propagating enolate anions and aggregation of active chain ends. In this study, the controlled synthesis of poly(1-adamatyl acrylate) (PAdA) was performed successfully for the first time via living anionic polymerization through investigation of the initiation systems of sec-butyllithium/diphenylethylene/lithium chloride (sec-BuLi/DPE/LiCl), diphenylmethylpotassium/diethylzinc (DPMK/Et2Zn), and sodium naphthalenide/dipenylethylene/diethylzinc (Na-Naph/DPE/Et2Zn) in tetrahydrofuran at -78 °C using custom glass-blowing and high-vacuum techniques. PAdA synthesized via anionic polymerization using DPMK with a large excess (more than 40-fold to DPMK) of Et2Zn as the ligand exhibited predicted molecular weights from 4.3more » to 71.8 kg/mol and polydispersity indices of around 1.10. In addition, the produced PAdAs exhibit a low level of isotactic content (mm triads of 2.1%). The block copolymers of AdA and methyl methacrylate (MMA) were obtained by sequential anionic polymerization, and the distinct living property of PAdA over other acrylates was demonstrated based on the observation that the resulting PAdA-b-PMMA block copolymers were formed with no residual PAdA homopolymer. The PAdA homopolymers exhibit a very high glass transition temperature (133 °C) and outstanding thermal stability (Td: 376 °C) as compared to other acrylic polymers such as poly(tert-butyl acrylate) and poly(methyl acrylate). These merits make PAdA a promising candidate for acrylic-based thermoplastic elastomers with high upper service temperature and enhanced mechanical strength.« less

  13. Combining living anionic polymerization with branching reactions in an iterative fashion to design branched polymers.

    PubMed

    Higashihara, Tomoya; Sugiyama, Kenji; Yoo, Hee-Soo; Hayashi, Mayumi; Hirao, Akira

    2010-06-16

    This paper reviews the precise synthesis of many-armed and multi-compositional star-branched polymers, exact graft (co)polymers, and structurally well-defined dendrimer-like star-branched polymers, which are synthetically difficult, by a commonly-featured iterative methodology combining living anionic polymerization with branched reactions to design branched polymers. The methodology basically involves only two synthetic steps; (a) preparation of a polymeric building block corresponding to each branched polymer and (b) connection of the resulting building unit to another unit. The synthetic steps were repeated in a stepwise fashion several times to successively synthesize a series of well-defined target branched polymers.

  14. Preparation and use of polymeric materials containing hydrophobic anions and plasticizers for separation of cesium and strontium

    DOEpatents

    Abney, K.D.; Kinkead, S.A.; Mason, C.F.V.; Rais, J.

    1997-09-09

    Preparation and use is described for polymeric materials containing hydrophobic anions and plasticizers for extraction of cesium and strontium. The use of polymeric materials containing plasticizers which are solvents for hydrophobic anions such as derivatives of cobalt dicarbollide or tetraphenylborate which are capable of extracting cesium and strontium ions from aqueous solutions in contact with the polymeric materials, is described. The polymeric material may also include a synergistic agent for a given ion like polyethylene glycol or a crown ether, for removal of radioactive isotopes of cesium and strontium from solutions of diverse composition and, in particular, for solutions containing large excess of sodium nitrate.

  15. Preparation and use of polymeric materials containing hydrophobic anions and plasticizers for separation of cesium and strontium

    DOEpatents

    Abney, Kent D.; Kinkead, Scott A.; Mason, Caroline F. V.; Rais, Jiri

    1997-01-01

    Preparation and use of polymeric materials containing hydrophobic anions and plasticizers for extraction of cesium and strontium. The use of polymeric materials containing plasticizers which are solvents for hydrophobic anions such as derivatives of cobalt dicarbollide or tetraphenylborate which are capable of extracting cesium and strontium ions from aqueous solutions in contact with the polymeric materials, is described. The polymeric material may also include a synergistic agent for a given ion like polyethylene glycol or a crown ether, for removal of radioactive isotopes of cesium and strontium from solutions of diverse composition and, in particular, for solutions containing large excess of sodium nitrate.

  16. How is the anionic tetrahedral intermediate involved in the isomerization of aspartyl peptides to iso-aspartyl ones? A DFT study on the tetra-peptide.

    PubMed

    Yamabe, Shinichi; Guan, Wei; Sakaki, Shigeyoshi

    2012-10-21

    An isomerization reaction of a tetra-peptide, Ac-Gly-Asp-Gly-Gly-NHMe → Ac-Gly-isoAsp-Gly-Gly-NHMe, was investigated by DFT calculations. Thirteen water molecules were added to the peptide for simulating proton transfers during the isomerization. As a starting analysis, the number (m) of water molecules participating in ready proton transfers was examined by the use of a small model system, H(3)C-NH-C(=O)-CH(2)-CH(2)-COOH and (H(2)O)(m). The m = 2 stepwise path was found to be of the smallest activation free energy. On the basis of this result, the first isomerization path of the tetra-peptide was obtained with four elementary processes. The m = 2 proton-transfer pattern is involved in them. A different proton transfer gives the second isomerization path with six elementary processes. The second path (with ionization) is more likely than the first one (without ionization). Formation of the five membered rings of the aminosuccinimidyl-residue and anionic tetrahedral intermediates enhances the encapsulation of H(3)O(+) through the wound tetra-peptide ring. The role of the hydrogen bonds on the encapsulation was discussed in terms of the optimized geometries of proton-transfer transition states and intermediates.

  17. Synthesis of functionalized asymmetric star polymers containing conductive polyacetylene segments by living anionic polymerization.

    PubMed

    Zhao, Youliang; Higashihara, Tomoya; Sugiyama, Kenji; Hirao, Akira

    2005-10-19

    Novel 3-arm ABC, 4-arm ABCD, and 5-arm ABCDE asymmetric star polymers comprising the conductive polyacetylene precursor, poly(4-methylphenyl vinyl sulfoxide) (PMePVSO), and other segments, such as polystyrene, poly(alpha-methylstyrene), poly(4-methoxystyrene), poly(4-trimethylsilylstyrene), and poly(4-methylstyrene), were synthesized by the methodology based on living anionic polymerization using DPE-functionalized polymers. This methodology involves the addition reaction of a DPE-functionalized polymer to a living anionic polymer followed by the living anionic polymerization of MePVSO initiated from the in situ formed polymer anion with two, three, or four polymer segments. The resultant asymmetric star polymers possessed predetermined molecular weights, narrow molecular weight distributions (Mw/Mn < 1.03), and desired compositions as confirmed by SEC, 1H NMR, SLS, and elemental analysis. After thermal treatment, the PMePVSO segment in the star polymer could be completely converted into a conductive polyacetylene segment, evident from TGA and elemental analysis. These asymmetric star polymers are expected to exhibit interesting solution properties and unique microphase-separated morphological suprastructures with potential applications in nanoscopic conductive materials. Moreover, this methodology can afford the target asymmetric star polymers with arm segments varying in a wide range and enables the synthesis of more complex macromolecular architectures.

  18. Epoxide Activated Anionic Polymerization: Application to the Synthesis of (Co)Polyethers with Controlled Structure and Tuned Properties

    NASA Astrophysics Data System (ADS)

    Labbe, Amelie; Rejsek, Virginie; Carlotti, Stephane; Deffieux, Alain

    A ring opening polymerization process allowing the fast and controlled anionic polymerization of epoxide monomers is described and applied to the synthesis of (co)polyethers with novel structure and composition. The approach is based on the simultaneous formation of complexes between an organometallic Lewis acid additive with both the anionic initiator and the monomer. In conjunction with the use of tetraalkylammonium or phosphonium salts as initiators, the addition of such additive allows the synthesis of polyethers and block copolyethers with controlled molar masses and narrow polydispersities, in hydrocarbon media, at low temperature, and in short reaction times. The low nucleophilic character of the propagating species involved in the polymerization avoids transfer to monomer, a side reaction which is often predominant in conventional anionic polymerizations. This also allows the controlled polymerization of functional epoxides such as glycidyl methacrylate and epichlorohydrin. Properties and potential applications of these new polyethers and copolyethers are also reported.

  19. Mixed tetrahedral anionic framework in the K{sub 3}Ga{sub 2}(PO{sub 4}){sub 3} crystal structure

    SciTech Connect

    Yakubovich, O. V.; Steele, I.; Kireev, V. V.

    2008-11-15

    The crystal structure of a new synthetic potassium gallophosphate K{sub 3}Ga{sub 2}(PO{sub 4}){sub 3} grown from a solution in the melt of a mixture of GaPO{sub 4} and K{sub 2}MoO{sub 4} is determined using X-ray diffraction (Bruker Smart diffractometer, 2{theta}{sub max}= 56.6{sup o}, R = 0.044 for 2931 reflections, T = 100 K). The main crystal data are as follows: a = 8.661(2) A, b = 17.002(4) A, c = 8.386(2) A, space group Pna2{sub 1}, Z= 4, and {rho}{sub calcd} = 2.91 g/cm{sup 3}. The synthesized crystals represent the third phase in the structure type previously established for the K{sub 3}Al{sub 2}[(As,P)O{sub 4}]{sub 3} compound. It is shown that the structure consists of a three-dimensional anionic microporous tetrahedral framework of the mixed type, which is formed by PO{sub 4} and GaO{sub 4} tetrahedra shared by vertices. Large-sized cations K{sup +} occupy channels of the zeolite-like framework. The crystal chemical features of the formation of structure types of compounds with mixed frameworks described by the general formula A{sub 3}{sup +}M{sub 2}{sup 3+}(TO{sub 4}){sub 3} (where A = K, Rb, (NH{sub 4}), Tl; M = Al, Ga, Fe, Sc, Yb; T = P, As) are analyzed.

  20. Poly-amido-saccharides: synthesis via anionic polymerization of a β-lactam sugar monomer.

    PubMed

    Dane, Eric L; Grinstaff, Mark W

    2012-10-03

    Enantiopure poly-amido-saccharides (PASs) with a defined molecular weight and narrow dispersity are synthesized using an anionic ring-opening polymerization of a β-lactam sugar monomer. The PASs have a previously unreported main chain structure that is composed of pyranose rings linked through the 1- and 2-positions by an amide with α-stereochemistry. The monomer is synthesized in one-step from benzyl-protected D-glucal and polymerized using mild reaction conditions to give degrees of polymerization ranging from 25 to >120 in high yield. Computational modeling reveals how the monomer's structure and steric bulk affect the thermodynamics and kinetics of polymerization. Protected and deprotected polymers and model compounds are characterized using a variety of methods (NMR, GPC, IR, DLS, etc.). On the basis of circular dichroism, the deprotected polymer possesses a regular secondary structure in aqueous solution, which agrees favorably with the prediction of a helical structure using molecular modeling. Furthermore, we provide evidence suggesting that the polymers bind the lectin concanavalin A at the same site as natural carbohydrates, showing the potential of these polymers to mimic natural polysaccharides. PASs offer the advantages associated with synthetic polymers, such as greater control over structure and derivitization. At the same time, they preserve many of the structural features of natural polysaccharides, such as a stereochemically regular, rigid pyranose backbone, that make natural carbohydrate polymers important materials both for their unique properties and useful applications.

  1. Ba{sub 3}GeS{sub 5} and Ba{sub 3}InS{sub 4}Cl: Interesting size effects originated from the tetrahedral anions

    SciTech Connect

    Pan, Ming-Yan; Xia, Sheng-Qing Liu, Xiao-Cun; Tao, Xu-Tang

    2014-11-15

    Two new barium chalcogenides, Ba{sub 3}GeS{sub 5} and Ba{sub 3}InS{sub 4}Cl, were synthesized by using high temperature solid-state reactions and their structures were determined by single-crystal X-ray diffraction technique. Despite the similar chemical formula, the structures of Ba{sub 3}GeS{sub 5} and Ba{sub 3}InS{sub 4}Cl are subtly different due to the size effects originated from the tetrahedral anions. Ba{sub 3}GeS{sub 5} crystallizes in the orthorhombic space group Pnma (no. 62) with cell parameters of a=12.0528(9) Å, b=9.5497(7) Å and c=8.5979(6) Å, while Ba{sub 3}InS{sub 4}Cl adopts a different tetragonal system (space group: I4/mcm, no. 140, a=b=8.3613(6) Å, c=14.3806(18) Å). The measured optical band gap of Ba{sub 3}GeS{sub 5} is 3.0 eV, a little smaller than the value of 3.42 eV in Ba{sub 3}InS{sub 4}Cl. Theoretical calculations by Wien2k are provided as well in order to better understand these results. - Graphical abstract: The polyhedral structure view for Ba{sub 3}GeS{sub 5} and Ba{sub 3}InS{sub 4}Cl in which Ba, S and Cl atoms are plotted in purple, red and green spheres. - Highlights: • Two new barium chalcogenides, Ba{sub 3}GeS{sub 5} and Ba{sub 3}InS{sub 4}Cl, were synthesized from the BaCl{sub 2}-flux reactions. • Their crystal structures feature discrete [MS{sub 4}] tetrahedra which embody interesting size effects. • Both compounds exhibit a band gap around 3.0 eV. • They are thermally stable up to 1073 K.

  2. 2-Isopropenyl-2-oxazoline: Well-Defined Homopolymers and Block Copolymers via Living Anionic Polymerization

    SciTech Connect

    Feng, Hongbo; Changez, Mohammad; Hong, Kunlun; Mays, Jimmy W.; Kang, Nam-Goo

    2016-12-23

    Poly(2-isopropenyl-2-oxazoline) (PIPOx) has drawn significant attention for numerous applications. However, the successful living anionic polymerization of 2-isopropenyl-2-oxazoline has not been reported previously. In this paper, we describe how well-defined PIPOx with quantitative yields, controlled molecular weights from 6800 to over 100 000 g/mol and low polydispersity indices (PDI ≤ 1.17) were synthesized successfully via living anionic polymerization using diphenylmethylpotassium/diethylzinc (DPM-K/Et2Zn) in tetrahydrofuran (THF) at 0 °C. In particular, we report the precise synthesis of well-defined PIPOx with the highest molecular weight ever reported (over 100 000 g/mol) and low PDI of 1.17. The resulting polymers were characterized by 1H and 13C nuclear magnetic resonance spectroscopy (NMR) along with size exclusion chromatography (SEC). Additionally, the reactivity of living PIPOx was investigated by crossover block copolymerization with styrene (St), 2-vinylpyridine (2VP), and methyl methacrylate (MMA). It was found that the nucleophilicity of living PIPOx is of this order: living PS > living P2VP > living PMMA > living PIPOx. The self-assembly behavior in bulk of PIPOx-b-PS-b-PIPOx triblock copolymers having different block ratios of 10:80:10 and 25:50:25 was studied using transmission electron microscopy (TEM). Finally, the formation of spherical and lamellar nanostructures, respectively, was observed.

  3. 2-Isopropenyl-2-oxazoline: Well-Defined Homopolymers and Block Copolymers via Living Anionic Polymerization

    DOE PAGES

    Feng, Hongbo; Changez, Mohammad; Hong, Kunlun; ...

    2016-12-23

    Poly(2-isopropenyl-2-oxazoline) (PIPOx) has drawn significant attention for numerous applications. However, the successful living anionic polymerization of 2-isopropenyl-2-oxazoline has not been reported previously. In this paper, we describe how well-defined PIPOx with quantitative yields, controlled molecular weights from 6800 to over 100 000 g/mol and low polydispersity indices (PDI ≤ 1.17) were synthesized successfully via living anionic polymerization using diphenylmethylpotassium/diethylzinc (DPM-K/Et2Zn) in tetrahydrofuran (THF) at 0 °C. In particular, we report the precise synthesis of well-defined PIPOx with the highest molecular weight ever reported (over 100 000 g/mol) and low PDI of 1.17. The resulting polymers were characterized by 1H andmore » 13C nuclear magnetic resonance spectroscopy (NMR) along with size exclusion chromatography (SEC). Additionally, the reactivity of living PIPOx was investigated by crossover block copolymerization with styrene (St), 2-vinylpyridine (2VP), and methyl methacrylate (MMA). It was found that the nucleophilicity of living PIPOx is of this order: living PS > living P2VP > living PMMA > living PIPOx. The self-assembly behavior in bulk of PIPOx-b-PS-b-PIPOx triblock copolymers having different block ratios of 10:80:10 and 25:50:25 was studied using transmission electron microscopy (TEM). Finally, the formation of spherical and lamellar nanostructures, respectively, was observed.« less

  4. A New Approach to the Living Anionic Polymerization of 4-Cyanostyrene

    SciTech Connect

    Driva, Paraskevi; Pickel, Deanna L; Mays, Jimmy; Baskaran, Durairaj

    2010-01-01

    A new approach to the synthesis of well-defined homopolymers of 4-cyanostyrene (4CNS) via anionic polymerization using high vacuum techniques is described. This synthetic route is based on the use of a solvent mixture of tetrahydrofuran and N,N-dimethylacetamide (THF/DMA, 4/1 v/v) in order to overcome the previously reported polymer insolubility issue and long reaction times. Our system afforded well-defined linear living P4CNSs having molecular weights up to 98,500 g/mol in less than 30 min and can be applied to the synthesis of P4CNS-based homopolymers and copolymers of various molecular architectures.

  5. Hierarchical Self-Assembled Structures from POSS-Containing Block Copolymers Synthesized by Living Anionic Polymerization

    SciTech Connect

    Hirai, Tomoyasu; Leolukman, Melvina; Jin, Sangwoo; Goseki, Raita; Ishida, Yoshihito; Kakimoto, Masa-aki; Hayakawa, Teruaki; Ree, Moonhor; Gopalan, Padma

    2010-03-16

    Two kinds of polyhedral oligomeric silsesquioxane (POSS)-containing block copolymers (BCPs), namely PS-b-PMAPOSS and PMMA-b-PMAPOSS, were synthesized by living anionic polymerization. A wide range of molecular weights were obtained with a very narrow polydispersity index of less than 1.09. The bulk samples prepared by slow evaporation from a polymer solution in chloroform exhibit well-defined microphase-separated structures with long-range order. Thermal annealing induced hierarchical structures consisting of a smaller length scale ordered crystalline POSS domains within the larger microphase-separated structures. We report detailed structural characterization of these hierarchical structures in bulk and thin films by transmission electron microscopy and grazing incidence wide-angle X-ray scattering (GIWAXS). On the basis of this structural analysis, we propose a model for the formation of an orthorhombic lattice structure through the aggregation of POSS segments which formed a helix-like structure.

  6. Imidazolium-Based Polymeric Materials as Alkaline Anion-Exchange Fuel Cell Membranes

    NASA Technical Reports Server (NTRS)

    Narayan, Sri R.; Yen, Shiao-Ping S.; Reddy, Prakash V.; Nair, Nanditha

    2012-01-01

    Polymer electrolyte membranes that conduct hydroxide ions have potential use in fuel cells. A variety of polystyrene-based quaternary ammonium hydroxides have been reported as anion exchange fuel cell membranes. However, the hydrolytic stability and conductivity of the commercially available membranes are not adequate to meet the requirements of fuel cell applications. When compared with commercially available membranes, polystyrene-imidazolium alkaline membrane electrolytes are more stable and more highly conducting. At the time of this reporting, this has been the first such usage for imidazolium-based polymeric materials for fuel cells. Imidazolium salts are known to be electrochemically stable over wide potential ranges. By controlling the relative ratio of imidazolium groups in polystyrene-imidazolium salts, their physiochemical properties could be modulated. Alkaline anion exchange membranes based on polystyrene-imidazolium hydroxide materials have been developed. The first step was to synthesize the poly(styrene-co-(1-((4-vinyl)methyl)-3- methylimidazolium) chloride through a free-radical polymerization. Casting of this material followed by in situ treatment of the membranes with sodium hydroxide solutions provided the corresponding hydroxide salts. Various ratios of the monomers 4-chloromoethylvinylbenzine (CMVB) and vinylbenzine (VB) provided various compositions of the polymer. The preferred material, due to the relative ease of casting the film, and its relatively low hygroscopic nature, was a 2:1 ratio of CMVB to VB. Testing confirmed that at room temperature, the new membranes outperformed commercially available membranes by a large margin. With fuel cells now in use at NASA and in transportation, and with defense potential, any improvement to fuel cell efficiency is a significant development.

  7. Pressure induced polymerization of acetylide anions in CaC2 and 107 fold enhancement of electrical conductivity

    DOE PAGES

    Zheng, Haiyan; Wang, Lijuan; Li, Kuo; ...

    2016-08-17

    Transformation between different types of carbon–carbon bonding in carbides often results in a dramatic change of physical and chemical properties. Under external pressure, unsaturated carbon atoms form new covalent bonds regardless of the electrostatic repulsion. It was predicted that calcium acetylide (also known as calcium carbide, CaC2) polymerizes to form calcium polyacetylide, calcium polyacenide and calcium graphenide under high pressure. In this work, the phase transitions of CaC2 under external pressure were systematically investigated, and the amorphous phase was studied in detail for the first time. Polycarbide anions like C66– are identified with gas chromatography-mass spectrometry and several other techniques,more » which evidences the pressure induced polymerization of the acetylide anions and suggests the existence of the polyacenide fragment. Additionally, the process of polymerization is accompanied with a 107 fold enhancement of the electrical conductivity. As a result, the polymerization of acetylide anions demonstrates that high pressure compression is a viable route to synthesize novel metal polycarbides and materials with extended carbon networks, while shedding light on the synthesis of more complicated metal organics.« less

  8. Synthesis of Block Copolymers of Varying Architecture Through Suppression of Transesterification during Coordinated Anionic Ring Opening Polymerization

    PubMed Central

    Lipik, Vitali T.; Abadie, Marc J. M.

    2012-01-01

    Well-defined di- and triblock copolymers consisting of ε-caprolactone (CL), L-lactide (LA), and trimethylene carbonate (TMC) were synthesized via “PLA first route” in coordinated anionic ring opening polymerization/copolymerization (CAROP) with tin (II) octoate as catalyst. The desired block structure was preserved by use of protective additive α-methylstyrene by preventing the transesterification side-reactions. MALDI-TOF analysis revealed that the protection mechanism is associated with α-methylstyrene and tin (II) octoate complexation. Additionally, it was shown that use of α-methylstyrene in ring opening polymerization allowed the formation of polyesters with high molar mass. PMID:22844286

  9. High temperature thermoplastic elastomers synthesized by living anionic polymerization in hydrocarbon solvent at room temperature

    DOE PAGES

    Schlegel, Ralf; Williams, Katherine; Voyloy, Dimitry; ...

    2016-03-30

    We present the synthesis and characterization of a new class of high temperature thermoplastic elastomers composed of polybenzofulvene–polyisoprene–polybenzofulvene (FIF) triblock copolymers. All copolymers were prepared by living anionic polymerization in benzene at room temperature. Homopolymerization and effects of additives on the glass transition temperature (Tg) of polybenzofulvene (PBF) were also investigated. Among all triblock copolymers studied, FIF with 14 vol % of PBF exhibited a maximum stress of 14.3 ± 1.3 MPa and strain at break of 1390 ± 66% from tensile tests. The stress–strain curves of FIF-10 and 14 were analyzed by a statistical molecular approach using a nonaffinemore » tube model to estimate the thermoplastic elastomer behavior. Dynamic mechanical analysis showed that the softening temperature of PBF in FIF was 145 °C, much higher than that of thermoplastic elastomers with polystyrene hard blocks. Microphase separation of FIF triblock copolymers was observed by small-angle X-ray scattering, even though long-range order was not achieved under the annealing conditions employed. Additionally, the microphase separation of the resulting triblock copolymers was examined by atomic force microscopy.« less

  10. High temperature thermoplastic elastomers synthesized by living anionic polymerization in hydrocarbon solvent at room temperature

    SciTech Connect

    Schlegel, Ralf; Williams, Katherine; Voyloy, Dimitry; Steren, Carlos A.; Goodwin, Andrew; Coughlin, E. Bryan; Gido, Samuel; Beiner, Mario; Hong, Kunlun; Kang, Nam -Goo; Mays, Jimmy; Wang, Weiyu; White, Benjamin T.

    2016-03-30

    We present the synthesis and characterization of a new class of high temperature thermoplastic elastomers composed of polybenzofulvene–polyisoprene–polybenzofulvene (FIF) triblock copolymers. All copolymers were prepared by living anionic polymerization in benzene at room temperature. Homopolymerization and effects of additives on the glass transition temperature (Tg) of polybenzofulvene (PBF) were also investigated. Among all triblock copolymers studied, FIF with 14 vol % of PBF exhibited a maximum stress of 14.3 ± 1.3 MPa and strain at break of 1390 ± 66% from tensile tests. The stress–strain curves of FIF-10 and 14 were analyzed by a statistical molecular approach using a nonaffine tube model to estimate the thermoplastic elastomer behavior. Dynamic mechanical analysis showed that the softening temperature of PBF in FIF was 145 °C, much higher than that of thermoplastic elastomers with polystyrene hard blocks. Microphase separation of FIF triblock copolymers was observed by small-angle X-ray scattering, even though long-range order was not achieved under the annealing conditions employed. Additionally, the microphase separation of the resulting triblock copolymers was examined by atomic force microscopy.

  11. Synthesis of bottlebrush polystyrenes with uniform, alternating, and gradient distributions of brushes via living anionic polymerization and hydrosilylation.

    PubMed

    Ma, Hongwei; Wang, Qiuyun; Sang, Wei; Han, Li; Liu, Pibo; Chen, Jun; Li, Yang; Wang, Yurong

    2015-04-01

    By combining living anionic polymerization and hydrosilylation, densely grafted bottlebrush polymers with controlled spacing of branch points are prepared. Dimethyl(4-vinylphenyl)silane and dimethyl(4-(1-phenylvinyl)phenyl)silane are anionically (co)polymerized to synthesize uniform, alternating, and gradient in-chain silyl-hydride (Si-H) functionalized backbones. The spacing of branch points is controlled effectively by regulating the distribution of Si-H groups along the backbones. Three backbones with a similar number of Si-H groups but variable distributions are used to synthesize corresponding bottlebrush polymers via hydrosilylation between the backbones and chain-end vinyl functionalized polystyrene. The uniformly grafted bottlebrush exhibits the highest hydrodynamic radius (Rh ) of 5.6 nm and the lowest Tg of 79 °C which may be attributed to its compact grafted structure. This methodology exhibits high efficiency and convenience for the construction of bottlebrushes with controlled distribution of brushes.

  12. Preparation a new sorbent based on polymeric ionic liquid for stir cake sorptive extraction of organic compounds and inorganic anions.

    PubMed

    Huang, Xiaojia; Wang, Yulei; Hong, Qiuyun; Liu, Yi; Yuan, Dongxing

    2013-11-01

    A new multi-interaction sorbent (MIS) based on polymeric ionic liquid was prepared and used as extractive medium of stir cake sorptive extraction (SCSE). In the presence of dimethyl sulfoxide, an ionic liquid, 1-vinylbenzyl-3-methylimidazolium chloride was used as monomer to copolymerize in situ with divinylbenzene to form the MIS. The influences of the content of monomer and the porogen solvent in the polymerization mixture on the extraction performance were investigated thoroughly. The MIS was characterized by infrared spectroscopy, elemental analysis, scanning electron microscopy and mercury intrusion porosimetry. Parabens and aromatic amines were used to investigate the extraction performance of MIS-SCSE for apolar and strongly polar analytes, respectively. The extraction parameters for parabens and aromatic amines were optimized. At the same time, simple and sensitive analytical methods for parabens and aromatic amines in real samples were developed by the combination of MIS-SCSE and HPLC/DAD. Some inorganic anions, such as F(-), Br(-), NO3(-), PO4(3-) and SO4(2-), were used to test the extraction performance of MIS-SCSE for anions. Results indicated that mechanism involved in the extraction of MIS is the multi-interaction modes including π-π, hydrophobic, hydrogen-bonding, dipole-dipole and anion-exchange interactions. Copyright © 2013 Elsevier B.V. All rights reserved.

  13. A new polymeric ionic liquid-based magnetic adsorbent for the extraction of inorganic anions in water samples.

    PubMed

    Chen, Lei; Huang, Xiaojia; Zhang, Yong; Yuan, Dongxing

    2015-07-17

    In this work, a novel type of polymeric ionic liquid (PIL)-based magnetic adsorbent was successfully synthesized and applied for the extraction and determination of seven inorganic anions in water samples by coupling with ion chromatography. The new adsorbent was synthesized by simple free radical copolymerization of 1-ally-3-vinylimidazolium chloride, ethylene glycol dimethacrylate and silica-coated magnetite. The adsorbent exhibited well-defined core-shell structure and good magnetic response ability. Furthermore, due to the presence of abundant anion-exchange groups in the PIL, the adsorbent displayed expected extraction performance for anions including F(-), Cl(-), Br(-), NO2(-), NO3(-), PO4(3-) and SO4(2-). Various experimental parameters that could affect the extraction performance, such as the amount of adsorbent, desorption solvent, extraction and desorption time, the pH value of sample solution were investigated in detail. Under the optimized conditions, low limits of detection (S/N=3) and quantification limits (S/N=10) of the proposed method for the target anions were achieved within the range of 0.061-0.73μg/L and 0.19-2.41μg/L, respectively. The repeatability was investigated by evaluating the intra-day, inter-day precisions and batch-to-batch reproducibility with relative standard deviations (RSDs) lower than 11%. At the same time, the method also showed high extraction speed, simplicity, practicality and low cost for the extraction inorganic anions. Finally, the proposed method was used to detect anions in different water samples successfully. The recoveries were in the range of 71.0-111%, and the RSDs were below 12% in the all cases.

  14. Synthesis and Characterization of Graft Copolymers Poly(isoprene-g-styrene) of High Molecular Weight by a Combination of Anionic Polymerization and Emulsion Polymerization

    SciTech Connect

    Wang, Wenwen; Wang, Weiyu; Li, Hui; Lu, Xinyi; Chen, Jihua; Kang, Nam-goo; Zhang, Qiuyu; Mays, Jimmy

    2015-01-14

    In this study, high molecular weight “comb-shaped” graft copolymers, poly(isoprene-g-styrene), with polyisoprene as the backbone and polystyrene as side chains, were synthesized via free radical emulsion polymerization by copolymerization of isoprene with a polystyrene macromonomer synthesized using anionic polymerization. A small amount of toluene was used in order to successfully disperse the macromonomer. Both a redox and thermal initiation system were used in the emulsion polymerization, and the latex particle size and distribution were investigated by dynamic light scattering. The structural characteristics of the macromonomer and comb graft copolymers were investigated through use of size exclusion chromatography, spectroscopy, microscopy, thermal analysis, and rheology. While the macromonomer was successfully copolymerized to obtain the desired multigraft copolymers, small amounts of unreacted macromonomer remained in the products, reflecting its reduced reactivity due to steric effects. Nevertheless, the multigraft copolymers obtained were very high in molecular weight (5–12 × 105 g/mol) and up to 10 branches per chain, on average, could be incorporated. A material incorporating 29 wt% polystyrene exhibits a disordered microphase separated morphology and elastomeric properties. As a result, these materials show promise as new, highly tunable, and potentially low cost thermoplastic elastomers.

  15. Synthesis and Characterization of Graft Copolymers Poly(isoprene-g-styrene) of High Molecular Weight by a Combination of Anionic Polymerization and Emulsion Polymerization

    DOE PAGES

    Wang, Wenwen; Wang, Weiyu; Li, Hui; ...

    2015-01-14

    In this study, high molecular weight “comb-shaped” graft copolymers, poly(isoprene-g-styrene), with polyisoprene as the backbone and polystyrene as side chains, were synthesized via free radical emulsion polymerization by copolymerization of isoprene with a polystyrene macromonomer synthesized using anionic polymerization. A small amount of toluene was used in order to successfully disperse the macromonomer. Both a redox and thermal initiation system were used in the emulsion polymerization, and the latex particle size and distribution were investigated by dynamic light scattering. The structural characteristics of the macromonomer and comb graft copolymers were investigated through use of size exclusion chromatography, spectroscopy, microscopy, thermalmore » analysis, and rheology. While the macromonomer was successfully copolymerized to obtain the desired multigraft copolymers, small amounts of unreacted macromonomer remained in the products, reflecting its reduced reactivity due to steric effects. Nevertheless, the multigraft copolymers obtained were very high in molecular weight (5–12 × 105 g/mol) and up to 10 branches per chain, on average, could be incorporated. A material incorporating 29 wt% polystyrene exhibits a disordered microphase separated morphology and elastomeric properties. As a result, these materials show promise as new, highly tunable, and potentially low cost thermoplastic elastomers.« less

  16. Layered double hydroxide/polyethylene terephthalate nanocomposites. Influence of the intercalated LDH anion and the type of polymerization heating method

    SciTech Connect

    Herrero, M.; Martinez-Gallegos, S.; Labajos, F.M.; Rives, V.

    2011-11-15

    Conventional and microwave heating routes have been used to prepare PET-LDH (polyethylene terephthalate-layered double hydroxide) composites with 1-10 wt% LDH by in situ polymerization. To enhance the compatibility between PET and the LDH, terephthalate or dodecyl sulphate had been previously intercalated in the LDH. PXRD and TEM were used to detect the degree of dispersion of the filler and the type of the polymeric composites obtained, and FTIR spectroscopy confirmed that the polymerization process had taken place. The thermal stability of these composites, as studied by thermogravimetric analysis, was enhanced when the microwave heating method was applied. Dodecyl sulphate was more effective than terephthalate to exfoliate the samples, which only occurred for the terephthalate ones under microwave irradiation. - Graphical abstract: Conventional and microwave heating routes were used to prepare PET-LDH (polyethylene terephthalate-layered double hydroxide) composites with 1-10 wt% LDH by in situ polymerization. To enhance the compatibility between PET and the LDH, terephthalate or dodecyl sulphate was previously intercalated into the LDH. The microwave process improves the dispersion and the thermal stability of nanocomposites due to the interaction of the microwave radiation and the dipolar properties of EG and the homogeneous heating. Highlights: > LDH-PET compatibility is enhanced by preintercalation of organic anions. > Dodecylsulphate performance is much better than that of terephthalate. > Microwave heating improves the thermal stability of the composites. > Microwave heating improves as well the dispersion of the inorganic phase.

  17. Anionic polymerization of oxadiazole-containing 2-vinylpyridine by precisely tuning nucleophilicity and the polyelectrolyte characteristics of the resulting polymers

    DOE PAGES

    Goodwin, Andrew; Goodwin, Kimberly M.; Wang, Weiyu; ...

    2016-09-01

    Anionic polymerization is one of the most powerful techniques for preparation of well-defined polymers. However, this well-known and widely employed polymerization technique encounters major limitations for the polymerization of functional monomers containing heteroatoms. This work presents the anionic polymerization of 2-phenyl-5-(6-vinylpyridin-3-yl)-1,3,4-oxadiazole (VPyOzP), a heteroatom monomer that contains both oxadiazole and pyridine substituents within the same pendant group, using various initiating systems based on diphenylmethyl potassium (DPM-K) and triphenylmethyl potassium (TPM-K). Remarkably, well-defined poly(2-phenyl-5-(6-vinylpyridin-3-yl)-1,3,4-oxadiazole) (PVPyOzP) polymers having predicted molecular weights (MW) ranging from 2200 to 21 100 g/mol and polydispersity indices (PDI) ranging from 1.11 to 1.15 were prepared with TPM-K,more » without any additional additives, at –78 °C. The effect of temperature on the polymerization of PVPyOzP was also studied at –78, –45, 0, and 25 °C, and it was observed that increasing the polymerization temperature produced materials with unpredictable MW’s and broader molecular weight distributions. Furthermore, the nucleophilicity of PVPyOzP was investigated through copolymerization with methyl methacrylate and acrylonitrile, where only living poly(methyl methacrylate) (PMMA) prepared by DPM-K/VPPy and in the absence of additives such as lithium chloride (LiCl) and diethyl zinc (ZnEt2) could be used to produce the well-defined block copolymer of PMMA-b-PVPyOzP. It was also demonstrated by sequential monomer addition that the nucleophilicity of living PVPyOzP is located between that of living PMMA and polyacrylonitrile (PAN). Here, the pyridine moiety of the pendant group also allowed for quaternization and produced PQVPyOzP homopolymer using methyl iodide (CH3I) and bis(trifluoromethylsulfonyl)amide [Tf2N–]. The resulting charged polymer and counterion complexes were manipulated and investigated

  18. Anionic polymerization of oxadiazole-containing 2-vinylpyridine by precisely tuning nucleophilicity and the polyelectrolyte characteristics of the resulting polymers

    SciTech Connect

    Goodwin, Andrew; Goodwin, Kimberly M.; Wang, Weiyu; Yu, Yong -Guen; Lee, Jae -Suk; Mahurin, Shannon M.; Dai, Sheng; Mays, Jimmy W.; Kang, Nam -Goo

    2016-09-01

    Anionic polymerization is one of the most powerful techniques for preparation of well-defined polymers. However, this well-known and widely employed polymerization technique encounters major limitations for the polymerization of functional monomers containing heteroatoms. This work presents the anionic polymerization of 2-phenyl-5-(6-vinylpyridin-3-yl)-1,3,4-oxadiazole (VPyOzP), a heteroatom monomer that contains both oxadiazole and pyridine substituents within the same pendant group, using various initiating systems based on diphenylmethyl potassium (DPM-K) and triphenylmethyl potassium (TPM-K). Remarkably, well-defined poly(2-phenyl-5-(6-vinylpyridin-3-yl)-1,3,4-oxadiazole) (PVPyOzP) polymers having predicted molecular weights (MW) ranging from 2200 to 21 100 g/mol and polydispersity indices (PDI) ranging from 1.11 to 1.15 were prepared with TPM-K, without any additional additives, at –78 °C. The effect of temperature on the polymerization of PVPyOzP was also studied at –78, –45, 0, and 25 °C, and it was observed that increasing the polymerization temperature produced materials with unpredictable MW’s and broader molecular weight distributions. Furthermore, the nucleophilicity of PVPyOzP was investigated through copolymerization with methyl methacrylate and acrylonitrile, where only living poly(methyl methacrylate) (PMMA) prepared by DPM-K/VPPy and in the absence of additives such as lithium chloride (LiCl) and diethyl zinc (ZnEt2) could be used to produce the well-defined block copolymer of PMMA-b-PVPyOzP. It was also demonstrated by sequential monomer addition that the nucleophilicity of living PVPyOzP is located between that of living PMMA and polyacrylonitrile (PAN). Here, the pyridine moiety of the pendant group also allowed for quaternization and produced PQVPyOzP homopolymer using methyl iodide (CH3I) and bis(trifluoromethylsulfonyl)amide [Tf2N]. The resulting charged polymer and counterion complexes

  19. Anionic polymerization of oxadiazole-containing 2-vinylpyridine by precisely tuning nucleophilicity and the polyelectrolyte characteristics of the resulting polymers

    SciTech Connect

    Goodwin, Andrew; Goodwin, Kimberly M.; Wang, Weiyu; Yu, Yong -Guen; Lee, Jae -Suk; Mahurin, Shannon M.; Dai, Sheng; Mays, Jimmy W.; Kang, Nam -Goo

    2016-09-01

    Anionic polymerization is one of the most powerful techniques for preparation of well-defined polymers. However, this well-known and widely employed polymerization technique encounters major limitations for the polymerization of functional monomers containing heteroatoms. This work presents the anionic polymerization of 2-phenyl-5-(6-vinylpyridin-3-yl)-1,3,4-oxadiazole (VPyOzP), a heteroatom monomer that contains both oxadiazole and pyridine substituents within the same pendant group, using various initiating systems based on diphenylmethyl potassium (DPM-K) and triphenylmethyl potassium (TPM-K). Remarkably, well-defined poly(2-phenyl-5-(6-vinylpyridin-3-yl)-1,3,4-oxadiazole) (PVPyOzP) polymers having predicted molecular weights (MW) ranging from 2200 to 21 100 g/mol and polydispersity indices (PDI) ranging from 1.11 to 1.15 were prepared with TPM-K, without any additional additives, at –78 °C. The effect of temperature on the polymerization of PVPyOzP was also studied at –78, –45, 0, and 25 °C, and it was observed that increasing the polymerization temperature produced materials with unpredictable MW’s and broader molecular weight distributions. Furthermore, the nucleophilicity of PVPyOzP was investigated through copolymerization with methyl methacrylate and acrylonitrile, where only living poly(methyl methacrylate) (PMMA) prepared by DPM-K/VPPy and in the absence of additives such as lithium chloride (LiCl) and diethyl zinc (ZnEt2) could be used to produce the well-defined block copolymer of PMMA-b-PVPyOzP. It was also demonstrated by sequential monomer addition that the nucleophilicity of living PVPyOzP is located between that of living PMMA and polyacrylonitrile (PAN). Here, the pyridine moiety of the pendant group also allowed for quaternization and produced PQVPyOzP homopolymer using methyl iodide (CH3I) and bis(trifluoromethylsulfonyl)amide [Tf2N]. The resulting charged polymer and counterion complexes

  20. Anionic oxidative polymerization: the synthesis of poly(phenylenedicyanovinylene) (PPCN2V).

    PubMed

    Moslin, Ryan M; Andrew, Trisha L; Kooi, Steven E; Swager, Timothy M

    2009-01-14

    A new polymerization technique that allows for the first-ever synthesis of poly(phenylenedicyanovinylene)s (PPCN2Vs) is described. PPCN2Vs, with their high electron affinities and structural versatility, seem ideally suited to address the need for new n-type polymers. Remarkably the polymers presented herein become more photoluminescent, in the thin film, under continuous irradiation.

  1. Sustainable Chiral Polyamides with High Melting Temperature via Enhanced Anionic Polymerization of a Menthone-Derived Lactam.

    PubMed

    Winnacker, Malte; Neumeier, Michael; Zhang, Xiaohan; Papadakis, Christine M; Rieger, Bernhard

    2016-05-01

    Polyamides are very important polymers that find applications from commodities up to the automotive and biomedical sectors, and their impact is continuously growing. The synthesis of structurally significant, chiral, and sustainable polyamides is described via a new, convenient, and solvent-free anionic polymerization of a biobased ε-lactam, which is obtained from the renewable terpenoid ketone l-menthone in a one-step synthesis. These polyamides are shown to have outstanding structural and thermal properties, which are thus introduced via the structure and chirality of the natural lactam monomer and which are discussed and compared with those of petroleum-based, established, and commercial polyamide Nylon-6. X-ray data reveal a remarkable degree of crystallinity in these green polymers and emphasize the impact of their structural features on the resulting properties.

  2. Synthesis of composite particles through emulsion polymerization based on silica/fluoroacrylate-siloxane using anionic reactive and nonionic surfactants.

    PubMed

    Qu, Ailan; Wen, Xiufang; Pi, Pihui; Cheng, Jiang; Yang, Zhuoru

    2008-01-01

    The composite particles with core/shell structure resulting from the combination of silica seed and hydrophobic copolymer (dodecafluoroheptyl methacrylate (DFMA), gamma-methacryloxypropyltriisopropoxidesilane (MAPTIPS), methyl methacrylate, butyl acrylate) were synthesized by emulsion polymerization. The amount of the silica seeds, concentration of reactive surfactant, as well as the addition of DFMA and MAPTIPS, have strong influences on the morphology of composite particles. It has been shown that it would be possible to produce stable organic/inorganic composite particles with inhomogeneous core/shell structure encapsulated by hydrophobic fluorinated acrylate even though using unmodified silica particles and admixture of anionic and nonionic surfactants. However, there was an obvious difference on the morphologies of core-shell structure whether the DFMA and MAPTIPS were added or not. It was concluded that two kinds of polymerization approaches might coexist in the presence of DFMA and MAPTIPS for raw silica. One clear advantage of this process is that there is only one silica bead for each composite particle. This kind of stable core-shell structural hybrid latex is useful for preparing high performance hydrophobic coating.

  3. Development of high-speed reactive processing system for carbon fiber-reinforced polyamide-6 composite: In-situ anionic ring-opening polymerization

    SciTech Connect

    Kim, Sang-Woo; Seong, Dong Gi; Yi, Jin-Woo; Um, Moon-Kwang

    2016-05-18

    In order to manufacture carbon fiber-reinforced polyamide-6 (PA-6) composite, we optimized the reactive processing system. The in-situ anionic ring-opening polymerization of ε-caprolactam was utilized with proper catalyst and initiator for PA-6 matrix. The mechanical properties such as tensile strength, inter-laminar shear strength and compressive strength of the produced carbon fiber-reinforced PA-6 composite were measured, which were compared with the corresponding scanning electron microscope (SEM) images to investigate the polymer properties as well as the interfacial interaction between fiber and polymer matrix. Furthermore, kinetics of in-situ anionic ring-opening polymerization of ε-caprolactam will be discussed in the viewpoint of increasing manufacturing speed and interfacial bonding between PA-6 matrix and carbon fiber during polymerization.

  4. Surface-initiated anionic polymerization of [1]silaferrocenophanes for the preparation of colloidal preceramic materials.

    PubMed

    Elbert, Johannes; Didzoleit, Haiko; Fasel, Claudia; Ionescu, Emanuel; Riedel, Ralf; Stühn, Bernd; Gallei, Markus

    2015-04-01

    A novel strategy for the preparation of poly(ferrocenylsilane) (PFS) immobilized on the surface of cross-linked polystyrene (PS) nanoparticles is reported. The ferrocene-containing core/shell architectures are shown to be excellent candidates as preceramic polymers yielding spherical ceramic materials consisting of iron silicide (Fe3 Si) and metallic iron after thermal treatment. For this purpose, dimethyl- and hydromethyl[1]silaferrocenophane monomers are polymerized by surface-initiated ring-opening polymerization upon taking advantage of residual vinylic moieties at the PS particle surface. A strategy for selective chain growth from the particle surface is developed without the formation of free PFS homopolymer in solution. The grafted particles are characterized using transmission electron microscopy (TEM) and dynamic light scattering (DLS). These particles are excellent precursors for ceramics as studied by thermogravimetric analysis (TGA). The composition of the ceramics is studied using X-ray diffraction (XRD) measurements, while the morphology is probed by scanning electron microscopy (SEM) revealing the original spherical shape of the precursor particles. Obtained ceramic materials- predominantly based on iron silicides-show ferromagnetic behavior as investigated by superconducting quantum interference device (SQUID) magnetization measurements at different temperatures. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Porous aromatic frameworks with anion-templated pore apertures serving as polymeric sieves

    NASA Astrophysics Data System (ADS)

    Yuan, Ye; Sun, Fuxing; Li, Lina; Cui, Peng; Zhu, Guangshan

    2014-06-01

    Owing to environmental pollution and energy depletion, efficient separation of energy gases has attracted widespread attention. Low-cost and efficient adsorbents for gas separation are greatly needed. Here we report a family of quaternary pyridinium-type porous aromatic frameworks with tunable channels. After carefully choosing and adjusting the sterically hindered counter ions via a facile ion exchange approach, the pore diameters are tuned at an angstrom scale in the range of 3.4-7 Å. The designed pore sizes may bring benefits to capturing or sieving gas molecules with varied diameters to separate them efficiently by size-exclusive effects. By combining their specific separation properties, a five-component (hydrogen, nitrogen, oxygen, carbon dioxide and methane) gas mixture can be separated completely. The porous aromatic frameworks may hold promise for practical and commercial applications as polymeric sieves.

  6. Pressure induced polymerization of acetylide anions in CaC 2 and 10 7 fold enhancement of electrical conductivity

    SciTech Connect

    Zheng, Haiyan; Wang, Lijuan; Li, Kuo; Yang, Youyou; Wang, Yajie; Wu, Jiajia; Dong, Xiao; Wang, Chun-Hai; Tulk, Christopher A.; Molaison, Jamie J.; Ivanov, Ilia N.; Feygenson, Mikhail; Yang, Wenge; Guthrie, Malcolm; Zhao, Yusheng; Mao, Ho-Kwang; Jin, Changqing

    2016-08-17

    Transformation between different types of carbon–carbon bonding in carbides often results in a dramatic change of physical and chemical properties. Under external pressure, unsaturated carbon atoms form new covalent bonds regardless of the electrostatic repulsion. It was predicted that calcium acetylide (also known as calcium carbide, CaC2) polymerizes to form calcium polyacetylide, calcium polyacenide and calcium graphenide under high pressure. In this work, the phase transitions of CaC2 under external pressure were systematically investigated, and the amorphous phase was studied in detail for the first time. Polycarbide anions like C66- are identified with gas chromatography-mass spectrometry and several other techniques, which evidences the pressure induced polymerization of the acetylide anions and suggests the existence of the polyacenide fragment. Additionally, the process of polymerization is accompanied with a 107 fold enhancement of the electrical conductivity. The polymerization of acetylide anions demonstrates that high pressure compression is a viable route to synthesize novel metal polycarbides and materials with extended carbon networks, while shedding light on the synthesis of more complicated metal organics.

  7. Pressure induced polymerization of acetylide anions in CaC2 and 107 fold enhancement of electrical conductivity

    SciTech Connect

    Zheng, Haiyan; Wang, Lijuan; Li, Kuo; Yang, Youyou; Wang, Yajie; Wu, Jiajia; Dong, Xiao; Wang, Chun -Hai; Tulk, Christopher A.; Molaison, Jamie J.; Ivanov, Ilia N.; Feygenson, Mikhail; Yang, Wenge; Guthrie, Malcolm; Zhao, Yusheng; Mao, Ho -Kwang; Jin, Changqing

    2016-08-17

    Transformation between different types of carbon–carbon bonding in carbides often results in a dramatic change of physical and chemical properties. Under external pressure, unsaturated carbon atoms form new covalent bonds regardless of the electrostatic repulsion. It was predicted that calcium acetylide (also known as calcium carbide, CaC2) polymerizes to form calcium polyacetylide, calcium polyacenide and calcium graphenide under high pressure. In this work, the phase transitions of CaC2 under external pressure were systematically investigated, and the amorphous phase was studied in detail for the first time. Polycarbide anions like C66– are identified with gas chromatography-mass spectrometry and several other techniques, which evidences the pressure induced polymerization of the acetylide anions and suggests the existence of the polyacenide fragment. Additionally, the process of polymerization is accompanied with a 107 fold enhancement of the electrical conductivity. As a result, the polymerization of acetylide anions demonstrates that high pressure compression is a viable route to synthesize novel metal polycarbides and materials with extended carbon networks, while shedding light on the synthesis of more complicated metal organics.

  8. Antimony(V) removal from water by hydrated ferric oxides supported by calcite sand and polymeric anion exchanger.

    PubMed

    Miao, Yangyang; Han, Feichao; Pan, Bingcai; Niu, Yingjie; Nie, Guangze; Lv, Lu

    2014-02-01

    We fabricated and characterized two hybrid adsorbents originated from hydrated ferric oxides (HFOs) using a polymeric anion exchanger D201 and calcite as host. The resultant adsorbents (denoted as HFO-201 and IOCCS) were employed for Sb(V) removal from water. Increasing solution pH from 3 to 9 apparently weakened Sb(V) removal by both composites, while increasing temperature from 293 to 313 K only improved Sb(V) uptake by IOCCS. HFO-201 exhibited much higher capacity for Sb(V) than for IOCCS in the absence of other anions in solution. Increasing ionic strength from 0.01 to 0.1 mol/L NaNO3 would result in a significant drop of the capacity of HFO-201 in the studied pH ranges; however, negligible effect was observed for IOCCS under similar conditions. Similarly, the competing chloride and sulfate pose more negative effect on Sb(V) adsorption by HFO-201 than by IOCCS, and the presence of silicate greatly decreased their adsorption simultaneously, while calcium ions were found to promote the adsorption of both adsorbents. XPS analysis further demonstrated that preferable Sb(V) adsorption by both hybrids was attributed to the inner sphere complexation of Sb(V) and HFO, and Ca(II) induced adsorption enhancement possibly resulted from the formation of HFO-Ca-Sb complexes. Column adsorption runs proved that Sb(V) in the synthetic water could be effectively removed from 30 microg/L to below 5 microg/L (the drinking water standard regulated by China), and the effective treatable volume of IOCCS was around 6 times as that of HFO-201, implying that HFO coatings onto calcite might be a more effective approach than immobilization inside D201.

  9. Metal-chelating polymers by anionic ring-opening polymerization and their use in quantitative mass cytometry.

    PubMed

    Illy, Nicolas; Majonis, Daniel; Herrera, Isaac; Ornatsky, Olga; Winnik, Mitchell A

    2012-08-13

    Metal-chelating polymers (MCPs) are important reagents for multiplexed immunoassays based on mass cytometry. The role of the polymer is to carry multiple copies of individual metal isotopes, typically as lanthanide ions, and to provide a reactive functionality for convenient attachment to a monoclonal antibody (mAb). For this application, the optimum combination of chain length, backbone structure, end group, pendant groups, and synthesis strategy has yet to be determined. Here we describe the synthesis of a new type of MCP based on anionic ring-opening polymerization of an activated cyclopropane (the diallyl ester of 1,1-cyclopropane dicarboxylic acid) using a combination of 2-furanmethanethiol and a phosphazene base as the initiator. This reaction takes place with rigorous control over molecular weight, yielding a polymer with a narrow molecular weight distribution, reactive pendant groups for introducing a metal chelator, and a functional end group with orthogonal reactivity for attaching the polymer to the mAbs. Following the ring-opening polymerization, a two-step transformation introduced diethylenetriaminepentaacetic acid (DTPA) chelating groups on each pendant group. The polymers were characterized by NMR, size exclusion chromatography (SEC), and thermogravimetric analysis (TGA). The binding properties toward Gd(3+) as a prototypical lanthanide (Ln) ion were also studied by isothermal titration calorimetry (ITC). Attachment to a mAb involves a Diels-Alder reaction of the terminal furan with a bismaleimide, followed by a Michael addition of a thiol on the mAb, generated by mild reduction of a disulfide bond in the hinge region. Polymer samples with a number average degree of polymerization of 35, with a binding capacity of 49.5 ± 6 Ln(3+) ions per chain, were loaded with 10 different types of Ln ions and conjugated to 10 different mAbs. A suite of metal-tagged Abs was tested by mass cytometry in a 10-plex single cell analysis of human adult peripheral blood

  10. Synthesis of Well-Defined Miktoarm Star Copolymer composed of Poly(3-hexylthiophene) and Poly(methyl methacrylate) via combining anionic polymerization and click reaction

    NASA Astrophysics Data System (ADS)

    Park, Jicheol; Moon, Hong Chul; Kim, Jin Kon

    2013-03-01

    We synthesized well-defined miktoarm star copolymer composed of regioregular poly(3-hexylthiophene) and poly(methyl methacrylate) ((P3HT)2- b-PMMA) by combining anionic polymerization and click reaction. First, we synthesized PMMA terminated with 1,3,5-tris(bromomethy)lbenzene (PMMA-(br)2) by anionic polymerization. Then, the bromide end groups transformed to azide group (PMMA-(N3)2) . For the synthesis (P3HT)2- b-PMMA, click reaction between ethynyl-capped P3HT and PMMA-(N3)2 was performed. The optical property and thin film morphology of (P3HT)2- b-PMMA were investigated by using UV-Vis spectra and atomic force microscopy, respectively.

  11. Facile modification of multi-walled carbon nanotubes-polymeric ionic liquids-coated solid-phase microextraction fibers by on-fiber anion exchange.

    PubMed

    Feng, Juanjuan; Sun, Min; Bu, Yanan; Luo, Chuannan

    2015-05-08

    In situ anion exchange has been proved to be an efficient method for facile modification of polymeric ionic liquids (PILs)-based stationary phases. In this work, an on-fiber anion exchange process was utilized to tune the extraction performance of a multi-walled carbon nanotubes (MWCNTs)-poly(1-vinyl-3-octylimidazolium bromide) (poly(VOIm(+)Br(-)))-coated solid-phase microextraction (SPME) fiber. MWCNTs were first coated onto the stainless steel wire through a layer-by-layer fabrication method and then the PILs were coated onto the MWCNTs physically. Anion of the MWCNTs-poly(VOIm(+)Br(-)) fiber was changed into bis(triflroromethanesulfonyl)imide (NTf2(-)) and 2-naphthalene-sulfonate (NapSO3(-)) by on-fiber anion exchange. Coupled to gas chromatography, the MWCNTs-poly(VOIm(+)Br(-)) fiber showed acceptable extraction efficiency for hydrophilic and hydrogen-bonding-donating alcohols, with limits of detection (LODs) in the range of 0.005-0.05μgmL(-1); after the anion exchange with NTf2(-), the obtained MWCNTs-poly(VOIm(+)NTf2(-)) fiber brought wide linear ranges for hydrophobic n-alkanes with correlation coefficient (R) ranging from 0.994 to 0.997; aromatic property of the fiber was enhanced by aromatic NapSO3(-) anions to get sufficient extraction capacity for phthalate esters and halogenated aromatic hydrocarbons. The MWCNTs-poly(VOIm(+)NapSO3(-)) fiber was finally applied to determine several halogenated aromatic hydrocarbons in groundwater of industrial park.

  12. Preparation of high-capacity, weak anion-exchange membranes by surface-initiated atom transfer radical polymerization of poly(glycidyl methacrylate) and subsequent derivatization with diethylamine

    NASA Astrophysics Data System (ADS)

    Qian, Xiaolei; Fan, Hua; Wang, Chaozhan; Wei, Yinmao

    2013-04-01

    Ion-exchange membrane is of importance for the development of membrane chromatography. In this work, a high-capacity anion-exchange membrane was prepared by grafting of glycidyl methacrylate (GMA) onto the surface of regenerated cellulose (RC) membranes via surface-initiated atom transfer radical polymerization (SI-ATRP) and subsequent derivatization with diethylamine. Attenuated total reflectance Fourier-transform infrared (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to characterize changes in the chemical functionality, surface topography and pore morphology of the modified membranes. The static capacity of the prepared anion-exchange membrane was evaluated with bovine serum albumin (BSA) as a model protein. The results indicated that the anion-exchange membrane which could reach a maximum capacity of 96 mg/mL for static adsorption possesses a higher adsorption capacity, and the adsorption capacity increases with the polymerization time. The effect of pH and salt concentration confirmed that the adsorption of BSA followed ion-exchange mechanism. The established method would have potential application in the preparation of anion-exchange membrane.

  13. Preparation of a new polymeric ionic liquid-based monolith for stir cake sorptive extraction and its application in the extraction of inorganic anions.

    PubMed

    Huang, Xiaojia; Chen, Linli; Yuan, Dongxing; Bi, Shangshang

    2012-07-27

    In this study, a novel stir cake sorptive extraction (SCSE) sorbent based on polymeric ionic liquid-based monolith (PILM) for the extraction of inorganic anions was prepared. In the presence of a porogen solvent containing 1-propanol and dimethylformamid, an ionic liquid, 1-ally-3-methylimidazolium chloride was used as monomer to copolymerize in situ with ethylene dimethacrylate to form PILM. The effect of preparation conditions such as ratio of functional monomer to cross-linker, content of porogenic solvent on the extraction efficiencies were investigated in detail. The PILM was characterized by elemental analysis, scanning electron microscopy, mercury intrusion porosimetry and infrared spectroscopy. In order to investigate the extraction capacity of PILM-SCSE for inorganic anions, the SCSE was combined with ion chromatography with conductivity detection, F(-), Cl(-), NO(2)(-), Br(-), NO(3)(-), PO(4)(3-) and SO(4)(2-) were selected as detected solutes. Several extractive parameters, including pH values in sample matrix, desorption solvent, extraction and desorption time were optimized. The results showed that under the optimum experimental conditions, low detection limits (S/N=3) and quantification limits (S/N=10) of the proposed method for the target anions were achieved within the range of 0.11-2.08 and 0.37-6.88 μg/L, respectively. The method also showed good linearity, simplicity, practicality and low cost for the extraction inorganic anions. Finally, the proposed method was successfully used to detect different water samples include commercial purified water, tab water and river water. Acceptable recoveries and satisfactory repeatability were obtained. To the best of our knowledge, this is the first to use polymeric ionic liquid to enrich inorganic anions.

  14. Separation of small inorganic anions using methacrylate-based anion-exchange monolithic column prepared by low temperature UV photo-polymerization.

    PubMed

    Takahashi, Mutsumi; Hirano, Tomohiko; Kitagawa, Shinya; Ohtani, Hajime

    2012-04-06

    A methacrylate-based anion-exchange monolithic column was prepared by a single-step UV photo-copolymerization of [2-(methacryloyloxy)ethyl]-trimethyl ammonium chloride, butylmethacrylate, and ethylene dimethacrylate at a low temperature of -15 °C. The anion-exchange column exhibited good separation efficiency for the small inorganic anions of NO(2)(-), Br(-), NO(3)(-), and I(-) in the isocratic mode. Under the conditions optimized using a mobile phase of 50% ACN containing 100mM of NaCl, the theoretical plate heights of the anions were within the range of 12.2-15.6 μm (N, 64,000-82,000 m(-1); k, 0.2-1.6); and a value of 9.4 μm (N, 110,000 m(-1)) was achieved for t(0). The flow resistance of the column was acceptably low with a permeability of 2.7 × 10(-13) m(2). Fast gradient elution at a flow rate of 32 mm/s resulted in rapid and precise separation of the inorganic anions of IO(3)(-), NO(2)(-), Br(-), NO(3)(-), and I(-) within 20s.

  15. Influence of doping anions on structure and properties of electro-polymerized polypyrrole counter electrodes for use in dye-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Zhang, Xuehua; Wang, Shasha; Lu, Shan; Su, Jia; He, Tao

    2014-01-01

    The nature of doping anions in polymerization solution has great influences on structure and properties of electro-polymerized polypyrrole (PPy) films and, thereby, on the electrocatalytic activity for I-/I3- redox reaction and accordingly the performance of dye-sensitized solar cells (DSSCs) based on PPy counter electrodes (CEs). The ions of chloride (Cl-), sulfate (SO42-), p-toluene sulfonate (TsO-), and dodecyl benzene sulfonate (DBS-) have been used as counter anions to prepare PPy films as CEs in the DSSCs. Compared with inorganic anions (Cl- and SO42-), the organic ones (TsO- and DBS-) afford more delocalized polarons. Moreover, PPy-DBS- films have the most fibrous or porous structure. Thus, PPy-DSB- has plenty of electrocatalytic active sites and high electric conductivity and, thereby, high electrocatalytic activity for I-/I3- redox reaction. Due to the synergistic effects of fibrous/porous structure, high conductivity and low interfacial charge transfer impedance, PPy-DBS- CE based DSSCs show the best photovoltaic conversion efficiency up to 5.40%, reaching 88% of the DSSCs based on Pt CE. Our results indicate that PPy thin films are promising candidates to replace Pt as the CEs for DSSCs, especially for the future flexible devices.

  16. Uniformity in Tetrahedral Hohlraums

    NASA Astrophysics Data System (ADS)

    Craxton, R. S.; Schnittman, J. D.; Pollaine, S. M.

    1996-11-01

    Tetrahedral hohlraums, i.e., spherical hohlraums with four laser entrance holes (LEH's), offer an alternative means of obtaining good time-independent capsule irradiation uniformity. Since the laser spots are spread fairly uniformly over the hohlraum wall, time-dependent uniformity swings are minimized. Using the 3-D view-factor code BUTTERCUP we have found, for both OMEGA and the NIF, that the uniformity is typically ~2% rms at all times, mainly in the Y_32 mode, but can be reduced to ~1% by independently varying the power in each beam. We have investigated the sensitivity of tetrahedral hohlraums to errors in beam-energy balance and pointing, and we have examined how large the LEH's must be to allow the beams to go through without refraction or absorption. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC03-92SF19460. *Also Lawrence Livermore National Laboratory.

  17. Chain Reaction Polymerization.

    ERIC Educational Resources Information Center

    McGrath, James E.

    1981-01-01

    The salient features and importance of chain-reaction polymerization are discussed, including such topics as the thermodynamics of polymerization, free-radical polymerization kinetics, radical polymerization processes, copolymers, and free-radical chain, anionic, cationic, coordination, and ring-opening polymerizations. (JN)

  18. Chain Reaction Polymerization.

    ERIC Educational Resources Information Center

    McGrath, James E.

    1981-01-01

    The salient features and importance of chain-reaction polymerization are discussed, including such topics as the thermodynamics of polymerization, free-radical polymerization kinetics, radical polymerization processes, copolymers, and free-radical chain, anionic, cationic, coordination, and ring-opening polymerizations. (JN)

  19. Vinylbenzyl quaternary ammonium-based polymeric monolith with hydrophilic interaction/strong anion exchange mixed-mode for pressurized capillary electrochromatography.

    PubMed

    Lin, Xucong; Feng, Shuhui; Jia, Wenchao; Ding, Kang; Xie, Zenghong

    2013-11-05

    A novel polymeric monolith with hydrophilic interaction and strong anion-exchange mixed-mode has been fabricated for pressurized capillary electrochromatography by an in situ copolymerization of vinylbenzyl trimethylammonium chloride (VBTA) and bisphenol A glycerolate dimethacrylate (BisGMA). The optimization of the polymerization mixture composition has been investigated, and column characteristics in terms of mechanical stability, permeability and reproducibility have been studied in detail. Linear responses between back pressure and flow rate have been achieved in different solvents. The absolute value of swelling propensity (SP) factor for poly(VBTA-co-BisGMA) monolith is 0.41, and the degree of permeability drop from pure ACN to water is about 45%. An acceptable mechanical stability of the column is obtained. The suitable reproducibility is also measured with the RSD for day-to-day (n=3) of retention time and column efficiency less than 3.3%, and the RSD for batch-to-batch (n=3) less than 5.3%, respectively. Under the optimum conditions, the mixed-mode of hydrophilic interaction and strong anion-exchange has been carried out, and efficient electrochromatography profiling of various polar compounds including neutral phenols, negatively charged benzoic acids and positively charged nucleic acid bases and nucleosides are achieved, respectively.

  20. Parallel Anisotropic Tetrahedral Adaptation

    NASA Technical Reports Server (NTRS)

    Park, Michael A.; Darmofal, David L.

    2008-01-01

    An adaptive method that robustly produces high aspect ratio tetrahedra to a general 3D metric specification without introducing hybrid semi-structured regions is presented. The elemental operators and higher-level logic is described with their respective domain-decomposed parallelizations. An anisotropic tetrahedral grid adaptation scheme is demonstrated for 1000-1 stretching for a simple cube geometry. This form of adaptation is applicable to more complex domain boundaries via a cut-cell approach as demonstrated by a parallel 3D supersonic simulation of a complex fighter aircraft. To avoid the assumptions and approximations required to form a metric to specify adaptation, an approach is introduced that directly evaluates interpolation error. The grid is adapted to reduce and equidistribute this interpolation error calculation without the use of an intervening anisotropic metric. Direct interpolation error adaptation is illustrated for 1D and 3D domains.

  1. Low-Energy Polymeric Phases of Alanates

    NASA Astrophysics Data System (ADS)

    Huan, Tran Doan; Amsler, Maximilian; Marques, Miguel A. L.; Botti, Silvana; Willand, Alexander; Goedecker, Stefan

    2013-03-01

    Low-energy structures of alanates are currently known to be described by patterns of isolated, nearly ideal tetrahedral [AlH4] anions and metal cations. We discover that the novel polymeric motif recently proposed for LiAlH4 plays a dominant role in a series of alanates, including LiAlH4, NaAlH4, KAlH4, Mg(AlH4)2, Ca(AlH4)2, and Sr(AlH4)2. In particular, most of the low-energy structures discovered for the whole series are characterized by networks of corner-sharing [AlH6] octahedra, forming wires and/or planes throughout the materials. Finally, for Mg(AlH4)2 and Sr(AlH4)2, we identify two polymeric phases to be lowest in energy at low temperatures.

  2. Incorporation of multi-walled carbon nanotubes in microspheres used as anion exchange resin via suspension polymerization

    NASA Astrophysics Data System (ADS)

    Fathy, Mahmoud; Abdel Moghny, Th.; Awadallah, Ahmed E.; El-Bellihi, Abdel-Hameed A.-A.

    2014-06-01

    Amination of vinylbenzyl chloride-divinylbenzene (VBC-DVB) copolymers is an effective method for preparation of anion-exchange resins. Conventionally, the starting polymer is produced by chloromethylation of a styrene-divinylbenzene copolymer that utilizes chloromethyl methyl ether, a known carcinogen. An alterative approach is to copolymerize vinylbenzyl chloride with divinylbenzene to generate the necessary VBC-DVB. This method provides precise control over the density of the ion-exchange groups. The regiochemistry of the vinylbenzyl chloride methods was realized using solvent-ion exchange groups. These resulting anion-exchange polymers were characterized by a variety of techniques such as analytical titrations, transform infrared spectroscopy and thermal gravimetric analysis. Testing of these copolymers for breakthrough was performed. The results indicate that these anion exchangers have a meaningful increase in thermal stability over commercial anionic exchange beads. Resins containing MWCNTs achieved anion exchange capacity value of 323.6 meq/100 g over than that of copolymer resins and that useful in water desalination or treatment.

  3. Precise synthesis of thermoreversible block copolymers containing reactive furfuryl groups via living anionic polymerization: the countercation effect on block copolymerization behavior

    SciTech Connect

    Kang, Beom-Goo; Pramanik, Nabendu B.; Singha, Nikhil K.; Lee, Jae-Suk; Mays, Jimmy

    2015-08-07

    The anionic block copolymerization of 4,4' -vinylphenyl-N,N-bis(4-tert-butylphenyl)benzenamine (A) with furfuryl isocyanate (B) was carried out using potassium naphthalenide (K-Naph) in tetrahydrofuran at -78 and -98 °C to prepare well-defined block copolymers containing furan groups for the formation of thermoreversible networks via a Diels Alder (DA) reaction. While no block copolymerization was observed in the absence of sodium tetraphenylborate (NaBPh4) due to side reactions, well-defined poly-(B-b-A-b-B) (PBAB) copolymers with controlled molecular weights (Mn = 18 700 19 500 g mol -1) and narrow molecular weight distributions (Mw/Mn = 1.08 -1.17) were successfully synthesized in the presence of excess NaBPh4. We prevented the occurrence of the undesirable side reactions during polymerization of B of NaBPh4, which results in the change in the countercation from K+ to Na+ for further polymerization of B. Moreover, the cross-linking via the DA reaction between the furan groups of PBAB and bismaleimide was proved by FT-IR and differential scanning calorimetry (DSC), and the thermoreversible properties of the cross-linked polymer were subsequently investigated using DSC and solubility testing.

  4. Anion exchange membrane prepared from simultaneous polymerization and quaternization of 4-vinyl pyridine for non-aqueous vanadium redox flow battery applications

    NASA Astrophysics Data System (ADS)

    Maurya, Sandip; Shin, Sung-Hee; Sung, Ki-Won; Moon, Seung-Hyeon

    2014-06-01

    A simple, single step and environmentally friendly process is developed for the synthesis of anion exchange membrane (AEM) by simultaneous polymerization and quaternization, unlike the conventional membrane synthesis which consists of separate polymerization and quaternization step. The membrane synthesis is carried out by dissolving polyvinyl chloride (PVC) in cyclohexanone along with 4-vinyl pyridine (4VP) and 1,4-dibromobutane (DBB) in the presence of thermal initiator benzoyl peroxide, followed by film casting to get thin and flexible AEMs. The membrane properties such as ion exchange capacity, ionic conductivity and swelling behaviour are tuned by varying the degree of crosslinking. These AEMs exhibit low vanadium permeability, while retaining good dimensional and chemical stability in an electrolyte solution, making them appropriate candidates for non-aqueous vanadium acetylacetonate redox flow battery (VRFB) applications. The optimized membrane displays ion exchange capacity and ionic conductivity of 2.0 mequiv g-1 and 0.105 mS cm-1, respectively, whereas the efficiency of 91.7%, 95.7% and 87.7% for coulombic, voltage and energy parameter in non-aqueous VRFB, respectively. This study reveals that the non-aqueous VRFB performance is greatly influenced by membrane properties; therefore the optimal control over the membrane properties is advantageous for the improved performance.

  5. Tetrahedral Order in Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Pleiner, Harald; Brand, Helmut R.

    2016-10-01

    We review the impact of tetrahedral order on the macroscopic dynamics of bent-core liquid crystals. We discuss tetrahedral order comparing with other types of orientational order, like nematic, polar nematic, polar smectic, and active polar order. In particular, we present hydrodynamic equations for phases, where only tetrahedral order exists or tetrahedral order is combined with nematic order. Among the latter, we discriminate between three cases, where the nematic director (a) orients along a fourfold, (b) along a threefold symmetry axis of the tetrahedral structure, or (c) is homogeneously uncorrelated with the tetrahedron. For the optically isotropic T d phase, which only has tetrahedral order, we focus on the coupling of flow with, e.g., temperature gradients and on the specific orientation behavior in external electric fields. For the transition to the nematic phase, electric fields lead to a temperature shift that is linear in the field strength. Electric fields induce nematic order, again linear in the field strength. If strong enough, electric fields can change the tetrahedral structure and symmetry leading to a polar phase. We briefly deal with the T phase that arises when tetrahedral order occurs in a system of chiral molecules. To case (a), defined above, belong (i) the non-polar, achiral, optically uniaxial D2d phase with ambidextrous helicity (due to a linear gradient free energy contribution) and with orientational frustration in external fields, (ii) the non-polar tetragonal S4 phase, (iii) the non-polar, orthorhombic D2 phase that is structurally chiral featuring ambidextrous chirality, (iv) the polar orthorhombic C2v phase, and (v) the polar, structurally chiral, monoclinic C2 phase. Case (b) results in a trigonal C3v phase that behaves like a biaxial polar nematic phase. An example for case (c) is a splay bend phase, where the ground state is inhomogeneous due to a linear gradient free energy contribution. Finally, we discuss some experiments

  6. Kinetics of Corrosion Inhibition of Aluminum in Acidic Media by Water-Soluble Natural Polymeric Pectates as Anionic Polyelectrolyte Inhibitors

    PubMed Central

    Hassan, Refat M.; Zaafarany, Ishaq A.

    2013-01-01

    Corrosion inhibition of aluminum (Al) in hydrochloric acid by anionic polyeletrolyte pectates (PEC) as a water-soluble natural polymer polysaccharide has been studied using both gasometric and weight loss techniques. The results drawn from these two techniques are comparable and exhibit negligible differences. The inhibition efficiency was found to increase with increasing inhibitor concentration and decrease with increasing temperature. The inhibition action of PEC on Al metal surface was found to obey the Freundlich isotherm. Factors such as the concentration and geometrical structure of the inhibitor, concentration of the corrosive medium, and temperature affecting the corrosion rates were examined. The kinetic parameters were evaluated and a suitable corrosion mechanism consistent with the kinetic results is discussed in the paper. PMID:28809282

  7. Streaming simplification of tetrahedral meshes.

    PubMed

    Vo, Huy T; Callahan, Steven P; Lindstrom, Peter; Pascucci, Valerio; Silva, Cláudio T

    2007-01-01

    Unstructured tetrahedral meshes are commonly used in scientific computing to represent scalar, vector, and tensor fields in three dimensions. Visualization of these meshes can be difficult to perform interactively due to their size and complexity. By reducing the size of the data, we can accomplish real-time visualization necessary for scientific analysis. We propose a two-step approach for streaming simplification of large tetrahedral meshes. Our algorithm arranges the data on disk in a streaming, I/O-efficient format that allows coherent access to the tetrahedral cells. A quadric-based simplification is sequentially performed on small portions of the mesh in-core. Our output is a coherent streaming mesh which facilitates future processing. Our technique is fast, produces high quality approximations, and operates out-of-core to process meshes too large for main memory.

  8. Combination of an anionic terminator multifunctional initiator and divergent carbanionic polymerization: application to the synthesis of dendrimer-like polymers and of asymmetric and miktoarm stars.

    PubMed

    Matmour, Rachid; Gnanou, Yves

    2008-01-30

    A new and versatile synthetic strategy that provides access to precisely defined and totally soluble multicarbanionic initiators has been implemented to obtain by divergent growth dendrimer-like samples of polystyrene (PS) (up to the seventh generation) or polybutadiene (PB) (up to the third generation) and also asymmetric and miktoarm stars. This strategy rests on lithium-halide exchange reactions to generate multicarbanionic species and on the design of an original reagent that can concomitantly react with living carbanionic chains/arms to deactivate them and produce multicarbanionic sites after exchange of its bromides against lithium. This reagent, 4,4'-dibromodiphenylethylene (1), functions as a TERminating agent and a Multifunctional INItiator (TERMINI), according to a concept first proposed by Percec in another context. Upon using this anionic TERMINI in living carbanionic polymerization and repeating the two steps of chain end derivatization by 1 and divergent arm growth from the multifunctional sites generated, perfectly defined dendrimer-like polystyrene and polybutadiene could be obtained up to the seventh generation for the former and up to the third generation for the latter. Each step, i.e., chain end modification and arm growth, was carefully monitored, and the dendrimer-like samples of PS and PB were all characterized by size exclusion chromatography equipped with a multiangle laser light scattering detector (SEC/LS) and high-temperature size exclusion chromatography equipped with a viscometric detector (HT-SEC). The viscosity behavior of these dendrimer-like polystyrenes--bell-shaped variation versus the number of generation--was found to be similar to that reported for regular dendrimers. This chemistry, namely this anionic TERMINI, was also exploited to derive three-arm asymmetric and miktoarm stars.

  9. Synthesis and characterization of anionic rare-earth metal amides stabilized by phenoxy-amido ligands and their catalytic behavior for the polymerization of lactide.

    PubMed

    Lu, Min; Yao, Yingming; Zhang, Yong; Shen, Qi

    2010-10-28

    A dianionic phenoxyamido ligand was the first to be used to stabilize organo-rare-earth metal amido complexes. Amine elimination reaction of Nd[N(TMS)(2)](3)(μ-Cl)Li(THF)(3) (TMS = SiMe(3)) with aminophenol [HNOH] {[HNOH] = N-p-methylphenyl(2-hydroxy-3,5-di-tert-butyl)benzylamine} in a 1 : 1 molar-ratio gave the anionic phenoxyamido neodymium amide [NO](2)Nd[N(TMS)(2)][Li(THF)](2) (2) in a low isolated yield. A further study revealed that the stoichiometric reactions of Ln[N(TMS)(2)](3)(μ-Cl)Li(THF)(3) with the lithium aminophenoxy [HNOLi(THF)](2) (1) in tetrahydrofuran (THF) gave the anionic rare-earth metal amido complexes [NO](2)Ln[N(TMS)(2)][Li(THF)](2) [Ln = Nd (2), Sm (3), Yb (4), Y (5)] in high isolated yields. All of these complexes are fully characterized. X-Ray structure determination revealed that complex 1 has a solvated dimeric structure, and complexes 2-5 are isostructural, and have solvated monomeric structures. Each of the rare-earth metal ions is coordinated by two oxygen atoms and two nitrogen atoms from two phenoxyamido ligands and one nitrogen atom from the N(TMS)(2) group to form a distorted trigonal bipyramidal geometry. Each of the lithium atoms in complexes 2-5 is coordinated with one oxygen atom and one nitrogen atom from two different phenoxyamido groups, and one oxygen atom from one THF molecule to form a trigonal planar geometry. Furthermore, the catalytic behavior of complexes 2-5 for the ring-opening polymerization of l-lactide was explored.

  10. Biocompatible Anionic Polymeric Microspheres as Priming Delivery System for Effetive HIV/AIDS Tat-Based Vaccines

    PubMed Central

    Titti, Fausto; Maggiorella, Maria T.; Ferrantelli, Flavia; Sernicola, Leonardo; Bellino, Stefania; Collacchi, Barbara; Belasio, Emanuele Fanales; Moretti, Sonia; Pavone Cossut, Maria Rosaria; Belli, Roberto; Olivieri, Erika; Farcomeni, Stefania; Compagnoni, Daniela; Michelini, Zuleika; Sabbatucci, Michela; Sparnacci, Katia; Tondelli, Luisa; Laus, Michele; Cafaro, Aurelio; Caputo, Antonella; Ensoli, Barbara

    2014-01-01

    Here we describe a prime-boost regimen of vaccination in Macaca fascicularis that combines priming with novel anionic microspheres designed to deliver the biologically active HIV-1 Tat protein and boosting with Tat in Alum. This regimen of immunization modulated the IgG subclass profile and elicited a balanced Th1-Th2 type of humoral and cellular responses. Remarkably, following intravenous challenge with SHIV89.6Pcy243, vaccinees significantly blunted acute viremia, as compared to control monkeys, and this control was associated with significantly lower CD4+ T cell depletion rate during the acute phase of infection and higher ability to resume the CD4+ T cell counts in the post-acute and chronic phases of infection. The long lasting control of viremia was associated with the persistence of high titers anti-Tat antibodies whose profile clearly distinguished vaccinees in controllers and viremics. Controllers, as opposed to vaccinated and viremic cynos, exhibited significantly higher pre-challenge antibody responses to peptides spanning the glutamine-rich and the RGD-integrin-binding regions of Tat. Finally, among vaccinees, titers of anti-Tat IgG1, IgG3 and IgG4 subclasses had a significant association with control of viremia in the acute and post-acute phases of infection. Altogether these findings indicate that the Tat/H1D/Alum regimen of immunization holds promise for next generation vaccines with Tat protein or other proteins for which maintenance of the native conformation and activity are critical for optimal immunogenicity. Our results also provide novel information on the role of anti-Tat responses in the prevention of HIV pathogenesis and for the design of new vaccine candidates. PMID:25356594

  11. Biocompatible anionic polymeric microspheres as priming delivery system for effetive HIV/AIDS Tat-based vaccines.

    PubMed

    Titti, Fausto; Maggiorella, Maria T; Ferrantelli, Flavia; Sernicola, Leonardo; Bellino, Stefania; Collacchi, Barbara; Fanales Belasio, Emanuele; Moretti, Sonia; Pavone Cossut, Maria Rosaria; Belli, Roberto; Olivieri, Erika; Farcomeni, Stefania; Compagnoni, Daniela; Michelini, Zuleika; Sabbatucci, Michela; Sparnacci, Katia; Tondelli, Luisa; Laus, Michele; Cafaro, Aurelio; Caputo, Antonella; Ensoli, Barbara

    2014-01-01

    Here we describe a prime-boost regimen of vaccination in Macaca fascicularis that combines priming with novel anionic microspheres designed to deliver the biologically active HIV-1 Tat protein and boosting with Tat in Alum. This regimen of immunization modulated the IgG subclass profile and elicited a balanced Th1-Th2 type of humoral and cellular responses. Remarkably, following intravenous challenge with SHIV89.6Pcy243, vaccinees significantly blunted acute viremia, as compared to control monkeys, and this control was associated with significantly lower CD4+ T cell depletion rate during the acute phase of infection and higher ability to resume the CD4+ T cell counts in the post-acute and chronic phases of infection. The long lasting control of viremia was associated with the persistence of high titers anti-Tat antibodies whose profile clearly distinguished vaccinees in controllers and viremics. Controllers, as opposed to vaccinated and viremic cynos, exhibited significantly higher pre-challenge antibody responses to peptides spanning the glutamine-rich and the RGD-integrin-binding regions of Tat. Finally, among vaccinees, titers of anti-Tat IgG1, IgG3 and IgG4 subclasses had a significant association with control of viremia in the acute and post-acute phases of infection. Altogether these findings indicate that the Tat/H1D/Alum regimen of immunization holds promise for next generation vaccines with Tat protein or other proteins for which maintenance of the native conformation and activity are critical for optimal immunogenicity. Our results also provide novel information on the role of anti-Tat responses in the prevention of HIV pathogenesis and for the design of new vaccine candidates.

  12. Thermal expansion and structural complexity of Ba silicates with tetrahedrally coordinated Si atoms

    NASA Astrophysics Data System (ADS)

    Gorelova, Liudmila A.; Bubnova, Rimma S.; Krivovichev, Sergey V.; Krzhizhanovskaya, Maria G.; Filatov, Stanislav K.

    2016-03-01

    Thermal expansion of Ba silicates with tetrahedrally coordinated Si atoms in the temperature range of 25-1100 °C had been studied by high-temperature X-ray powder diffraction. The volume thermal expansion coefficients (TECs) are in the range 41-50×10-6 °C-1 with an average value of <αV > = 45 ×10-6 °C-1. In the structures with chain and layered silicate anions, thermal expansion is anisotropic: the direction of maximal TEC is parallel to the extension of the zweier chains of silicate tetrahedra, which are strained owing to the interactions with Ba2+. The strain is released during thermal expansion due to the increasing effective size of Ba2+ induced by thermal vibrations. Information-theoretic analysis of the structural and topological complexities of Ba silicates indicates that their structural complexity is a function of the topological complexity of their silicate anions. The latter displays a non-linear behaviour with increasing SiO2 content (=the increasing degree of polymerization and increasing dimensionality): it starts from simple topologies, reaches a maximum at topologies of intermediate complexity, and ends up at simple topologies again. The specificity of the interactions of Ba2+ with the silicate anions results in higher complexity of high-temperature α-BaSi2O5 compared to that of low-temperature β-BaSi2O5. This uncommon behaviour may be explained by the vibrational advantages provided by flatter and more complex silicate layers in the α-phase, which overcome negative differences in configurational entropies of the two modifications apparent in the differences of their structural Shannon information.

  13. Growth of PbTe nanorods controlled by polymerized tellurium anions and metal(II) amides via composite-hydroxide-mediated approach

    SciTech Connect

    Wan Buyong; Hu Chenguo; Liu Hong; Xiong Yufeng; Li Feiyun; Xi Yi; He Xiaoshan

    2009-09-15

    The pure face-centered-cubic PbTe nanorods have been synthesized by the composite-hydroxide-mediated approach using hydrazine as a reducing agent. The method is based on reaction among reactants in the melts of potassium hydroxide and sodium hydroxide eutectic at 170-220 deg. C and normal atmosphere without using any organic dispersant or surface-capping agent. Scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and energy dispersive X-ray spectroscopy were used to characterize the structure, morphology and composition of the samples. The diameters of nanorods are almost fixed, while the lengths can be tunable under different growth time and temperatures. The growth mechanism of PbTe nanorods is investigated via UV-vis absorption, demonstrating that polymerized tellurium anions and metal(II) amides in the hydrazine hydroxide melts could control the crystallization and growth process of PbTe nanostructures. The band gap of as-synthesized PbTe nanorods has been calculated based on UV-vis-NIR optical diffuse reflectance spectra data.

  14. A cell wall-bound anionic peroxidase, PtrPO21, is involved in lignin polymerization in Populus trichocarpa

    SciTech Connect

    Lin, Chien-Yuan; Li, Quanzi; Tunlaya-Anukit, Sermsawat; Shi, Rui; Sun, Ying-Hsuan; Wang, Jack P.; Liu, Jie; Loziuk, Philip; Edmunds, Charles W.; Miller, Zachary D.; Peszlen, Ilona; Muddiman, David C.; Sederoff, Ronald R.; Chiang, Vincent L.

    2016-03-11

    Class III peroxidases are members of a large plant-specific sequence-heterogeneous protein family. Several sequence-conserved homologs have been associated with lignin polymerization in Arabidopsis thaliana, Oryza sativa, Nicotiana tabacum, Zinnia elegans, Picea abies, and Pinus sylvestris. In Populus trichocarpa, a model species for studies of wood formation, the peroxidases involved in lignin biosynthesis have not yet been identified. To do this, we retrieved sequences of all PtrPOs from Peroxibase and conducted RNA-seq to identify candidates. Transcripts from 42 PtrPOs were detected in stem differentiating xylem (SDX) and four of them are the most xylem-abundant (PtrPO12, PtrPO21, PtrPO42, and PtrPO64). PtrPO21 shows xylem-specific expression similar to that of genes encoding the monolignol biosynthetic enzymes. Using protein cleavage-isotope dilution mass spectrometry, PtrPO21 is detected only in the cell wall fraction and not in the soluble fraction. Downregulated transgenics of PtrPO21 have a lignin reduction of ~20% with subunit composition (S/G ratio) similar to wild type. The transgenics show a growth reduction and reddish color of stem wood. The modulus of elasticity (MOE) of the stems of the downregulated PtrPO21-line 8 can be reduced to ~60% of wild type. Differentially expressed gene (DEG) analysis of PtrPO21 downregulated transgenics identified a significant overexpression of PtPrx35, suggesting a compensatory effect within the peroxidase family. No significant changes in the expression of the 49 P. trichocarpa laccases (PtrLACs) were observed.

  15. Anionic constitution of 1-atmosphere silicate melts: implications for the structure of igneous melts.

    PubMed

    Virgo, D; Mysen, B O; Kushiro, I

    1980-06-20

    A structural model is proposed for the polymeric units in silicate melts quenched at 1 atmosphere. The anionic units that have been identified by the use of Raman spectroscopy are SiO(4)(4-) monomers, Si(2)O(7)(6-) dimers, SiO(3)(2-) chains or rings, Si(2)O(5)(2-) sheets, and SiO(2) three-dimensional units. The coexisting anionic species are related to specific ranges of the ratio of nonbridging oxygens to tetrahedrally coordinated cations (NBO/Si). In melts with 2.0 < NBO/Si < approximately 4.0, the equilibrium is of the type [See equation in the PDF file]. In melts with NBO/Si approximately 1.0 to 2.0, the equilibrium anionic species are given by [See equation in the PDF file]. In alkali-silicate melts with NBO/Si <~ 1.3 and in aluminosilicate melts with NBO/T < 1.0, where T is (Si + Al), the anionic species in equilibrium are given by [See equation in the PDF file]. In multicomponent melts with compositions corresponding to those of the major igneous rocks, the anionic species are TO(2), T(2)O(5), T(2)O(6), and TO(4), and the coexisting polymeric units are determined by the second and third of these disproportionation reactions.

  16. Urea-functionalized crystalline capsules for recognition and separation of tetrahedral oxoanions

    SciTech Connect

    Custelcean, Radu

    2012-12-21

    We reviewed the persistent ability of tripodal TREN-based tris-urea receptors (TREN = tris(2-aminoethyl)amine) to self-assemble with a variety of oxoanions into dimeric capsules upon crystallization. The capsule crystallization allows for charge-, shape-, and size-selective encapsulation of tetrahedral XO4n-anions (n = 2,3), and provides an effective way to separate these anions from competitive aqueous environments.

  17. The Kontsevich tetrahedral flow revisited

    NASA Astrophysics Data System (ADS)

    Bouisaghouane, A.; Buring, R.; Kiselev, A.

    2017-09-01

    We prove that the Kontsevich tetrahedral flow P ˙ =Qa:b(P) , the right-hand side of which is a linear combination of two differential monomials of degree four in a bi-vector P on an affine real Poisson manifold Nn, does infinitesimally preserve the space of Poisson bi-vectors on Nn if and only if the two monomials in Qa:b(P) are balanced by the ratio a : b = 1 : 6. The proof is explicit; it is written in the language of Kontsevich graphs.

  18. Coding a coordination-driven self-assembly via a hydrogen bond-directed solid-state synthesis: an unexpected chiral tetrahedral capsule.

    PubMed

    Hamilton, Tamara D; Bucar, Dejan-Kresimir; MacGillivray, Leonard R

    2007-04-28

    An achiral ligand, synthesized in the solid state via a coded hydrogen bond-directed organic synthesis, self-assembles with Cu(II) ions to form a chiral tetrahedral capsule that hosts an anion as a guest.

  19. The NASA Tetrahedral Unstructured Software System (TETRUSS)

    DTIC Science & Technology

    2000-09-01

    large angles of incidence. AGARD CP-247, High Angle of Attack Aerodynamics, Paper No. 15, January 1979. [34] Krist S , Biedron R. and Rumsey C. CFL3D...tetrahedral, Navier-Stokes, aeroelastic, design Abstact The NASA Tetrahedral Unstructured Software System (TetrUSS) was developed during the 1990’ s to...NASA Tetrahedral Unstructured Software System (TETRUSS) 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR( S ) 5d. PROJECT

  20. Composite materials with improved properties in compression. Appendix 5. Synthesis and anionic ring-opening polymerization of 1-germa-1,1- dimethyl(3,4,c) thieno cyclopentane. Interim report

    SciTech Connect

    Zhou, S.Q.; Weber, W.P.

    1990-05-09

    While there has been extensive work on several types of polymers having silicon in the main chain due to their scientific and industrial importance, few studies on polymers containing germanium in the backbone have been reported. Despite this limited research, polygermanes have been observed to have interesting properties. For example, they have been found to be photoactive. They undergo photobleaching as well as to have thermochromic properties. Most recently, germylenes, stable divalent germanium species, have been found to undergo a novel oxidation-reduction copolymerization with benzoquinones. Anionic ring opening polymerization of I yields III, a carbogermanium polymer in which both carbon and germanium atoms make up the polymer backbone.

  1. Building Tetrahedral Kites. Grades 6-8.

    ERIC Educational Resources Information Center

    Rushton, Erik; Ryan, Emily; Swift, Charles

    Working in teams of four, students build a tetrahedral kite following a specific set of directions and using specific provided materials. Students use basic processes of manufacturing systems-- cutting, shaping, forming, conditioning, assembling, joining, finishing, and quality control--to manufacture a complete tetrahedral kite within a given…

  2. Low-Energy Polymeric Phases of Alanates

    NASA Astrophysics Data System (ADS)

    Tran, Huan; Amsler, Maximilian; Marques, Miguel; Botti, Silvana; Willand, Alexander; Goedecker, Stefan

    2013-03-01

    Low-energy structures of alanates are currently known to be described by patterns of isolated, nearly ideal tetrahedral [AlH4] anions and metal cations. We discover that the novel polymeric motif recently proposed for LiAlH4 plays a dominant role in a series of alanates, including LiAlH4, NaAlH4, KAlH4, Mg(AlH4)2, Ca(AlH4)2 and Sr(AlH4)2. In particular, most of the low-energy structures discovered for the whole series are characterized by networks of corner-sharing [AlH6] octahedra, forming wires and/or planes throughout the materials. Finally, for Mg(AlH4)2 and Sr(AlH4)2, we identify two polymeric phases to be lowest in energy at low temperatures. Work supported by Swiss NSF. Computational resources were provided by the Swiss National Supercomputing Center (CSCS) in Lugano.

  3. Au40: A Large Tetrahedral Magic Cluster

    SciTech Connect

    Jiang, Deen; Walter, Michael

    2011-01-01

    40 is a magic number for tetrahedral symmetry predicted in both nuclear physics and the electronic jellium model. We show that Au{sub 40} could be such a magic cluster from density functional theory-based basin hopping for global minimization. The putative global minimum found for Au{sub 40} has a twisted pyramid structure, reminiscent of the famous tetrahedral Au{sub 20}, and a sizable HOMO-LUMO gap of 0.69 eV, indicating its molecular nature. Analysis of the electronic states reveals that the gap is related to shell closings of the metallic electrons in a tetrahedrally distorted effective potential.

  4. MMS Spacecraft Transition to Tetrahedral Flying Formation

    NASA Image and Video Library

    In the latter half of July 2015, the four satellites of the Magnetosphere Multi-scale (MMS) mission move into their tetrahedral formation flying configuration as part of the checkout for the scienc...

  5. Octahedrality versus tetrahedrality in stoichiometric ceria nanoparticles.

    PubMed

    Migani, Annapaola; Neyman, Konstantin M; Bromley, Stefan T

    2012-05-04

    We predict that tetrahedral Ce(n)O(2n) nanoparticles <2 nm in size become more stable than those experimentally observed at larger sizes with truncated octahedral morphologies, based on global optimisation and density functional calculations.

  6. Covalent Polymers Containing Discrete Heterocyclic Anion Receptors

    NASA Astrophysics Data System (ADS)

    Rambo, Brett M.; Silver, Eric S.; Bielawski, Christopher W.; Sessler, Jonathan L.

    This chapter covers recent advances in the development of polymeric materials containing discrete heterocyclic anion receptors, and focuses on advances in anion binding and chemosensor chemistry. The development of polymers specific for anionic species is a relatively new and flourishing area of materials chemistry. The incorporation of heterocyclic receptors capable of complexing anions through noncovalent interactions (e.g., hydrogen bonding and electrostatic interactions) provides a route to not only sensitive but also selective polymeric materials. Furthermore, these systems have been utilized in the development of polymers capable of extracting anionic species from aqueous media. These latter materials may lead to advances in water purification and treatment of diseases resulting from surplus ions.

  7. Tetrahedrality and hydrogen bonds in water

    NASA Astrophysics Data System (ADS)

    Székely, Eszter; Varga, Imre K.; Baranyai, András

    2016-06-01

    We carried out extensive calculations of liquid water at different temperatures and pressures using the BK3 model suggested recently [P. T. Kiss and A. Baranyai, J. Chem. Phys. 138, 204507 (2013)]. In particular, we were interested in undercooled regions to observe the propensity of water to form tetrahedral coordination of closest neighbors around a central molecule. We compared the found tetrahedral order with the number of hydrogen bonds and with the partial pair correlation functions unfolded as distributions of the closest, the second closest, etc. neighbors. We found that contrary to the number of hydrogen bonds, tetrahedrality changes substantially with state variables. Not only the number of tetrahedral arrangements increases with lowering the pressure, the density, and the temperature but the domain size of connecting tetrahedral structures as well. The difference in tetrahedrality is very pronounced between the two sides of the Widom line and even more so between the low density amorphous (LDA) and high density amorphous (HDA) phases. We observed that in liquid water and in HDA, the 5th water molecule, contrary to ice and LDA, is positioned between the first and the second coordination shell. We found no convincing evidence of structural heterogeneity or regions referring to structural transition.

  8. Hydrogeniridate(VI) anion and the geometries of tetrahedral oxo-anions.

    PubMed

    Weller, Mark T; Galati, Rosa

    2014-06-02

    The compound KHIrO4, potassium hydrogentetraoxidoiridate(VI)(1-), crystallizes in a Scheelite-type structure containing discrete, slightly flattened, [Ir(O3OH)](-) tetrahedra--the first observation of a group 9 element in the 6+ oxidation state as an oxoanion.

  9. A fabrication strategy for nanosized zero valent iron (nZVI)-polymeric anion exchanger composites with tunable structure for nitrate reduction.

    PubMed

    Jiang, Zhenmao; Zhang, Shujuan; Pan, Bingcai; Wang, Wenfeng; Wang, Xiaoshu; Lv, Lu; Zhang, Weiming; Zhang, Quanxing

    2012-09-30

    To reveal how the distribution of nanoscale zero-valent iron (nZVI) affect their reduction efficiency of its polymer-based composites and to further develop a simple strategy to tune the structure of the composites, we prepared four nZVI-polymerstyrene anion exchanger composites with similar nZVI loadings (13.5-14.4 Fe % in mass) but different distributions just through varying the concentration of NaBH(4) (0.9, 1.8, 3.6, and 7.2% in mass) solution during reduction of nZVI precursor (FeCl(4)(-) anions). As observed by SEM-EDX images, increasing the NaBH(4) concentration resulted in a more uniform nZVI distribution within the polymer, and thereto higher NH(4)(+)N production, faster reaction rate and more gaseous products during its reduction of nitrate and nitrite. nZVI distribution of the composites was suggested to greatly depend upon two processes, the hydrolyzation of anionic FeCl(4)(-) into cationic Fe(3+) and the reduction of both Fe(III) species by NaBH(4). Higher NaBH(4) concentration favored its faster diffusion into the inside polymer and in situ reduction of Fe(III) species into nZVI, causing a more uniform nZVI distribution. The results reported herein suggest that adjusting the NaBH(4) concentration was a simple and effective method to control the nZVI distribution in the supporting polymers, and indirectly tune the reactivity of the resultant nZVI hybrids.

  10. Anionic metabolite profiling by capillary electrophoresis-mass spectrometry using a noncovalent polymeric coating. Orange juice and wine as case studies.

    PubMed

    Acunha, Tanize; Simó, Carolina; Ibáñez, Clara; Gallardo, Alberto; Cifuentes, Alejandro

    2016-01-08

    In several metabolomic studies, it has already been demonstrated that capillary electrophoresis hyphenated to mass spectrometry (CE-MS) can detect an important group of highly polar and ionized metabolites that are overseen by techniques such as NMR, LC-MS and GC-MS, providing complementary information. In this work, we present a strategy for anionic metabolite profiling by CE-MS using a cationic capillary coating. The polymer, abbreviated as PTH, is composed of a poly-(N,N,N',N'-tetraethyldiethylenetriamine, N-(2-hydroxypropyl) methacrylamide, TEDETAMA-co-HPMA (50:50) copolymer. A CE-MS method based on PTH-coating was optimized for the analysis of a group of 16 standard anionic metabolites. Separation was achieved within 12min, with high separation efficiency (up to 92,000 theoretical plates per meter), and good repeatability, namely, relative standard deviation values for migration times and peak areas were below 0.2 and 2.1%, respectively. The optimized method allowed the detection of 87 metabolites in orange juice and 142 metabolites in red wine, demonstrating the good possibilities of this strategy for metabolomic applications. Copyright © 2015 Elsevier B.V. All rights reserved.

  11. Preparation of a mixed-mode hydrophilic interaction/anion-exchange polymeric monolithic stationary phase for capillary liquid chromatography of polar analytes.

    PubMed

    Lin, Jian; Lin, Jia; Lin, Xucong; Xie, Zenghong

    2009-01-30

    A novel cationic hydrophilic interaction monolithic stationary phase based on the copolymerization of 2-(methacryloyloxy)ethyltrimethylammonium methyl sulfate (META) and pentaerythritol triacrylate (PETA) in a binary porogenic solvent consisting of cyclohexanol/ethylene glycol was designed for performing capillary liquid chromatography. While META functioned as both the ion-exchange sites and polar ligand provider, the PETA, a trivinyl monomer, was introduced as cross-linker. The monolithic stationary phases with different properties were easily prepared by adjusting the amount of META in the polymerization solution as well as the composition of the porogenic solvent. The hydrophilicity of the monolith increased with increasing content of META in the polymerization mixture. A typical hydrophilic interaction chromatography mechanism was observed when the content of acetonitrile in the mobile phase was higher than 20%. The poly(META-co-PETA) monolith showed very good selectivity for neutral, basic and acidic polar analytes. For polar-charged analytes, both hydrophilic interaction and electrostatic interaction contributed to their retention. Peak tailing of basic compounds was avoided and the efficient separation of benzoic acid derivatives was obtained.

  12. Soap-free emulsion polymerization of poly (methyl methacrylate-co-butyl acrylate): effects of anionic comonomers and methanol on the different characteristics of the latexes.

    PubMed

    Adelnia, Hossein; Pourmahdian, Saeed

    2014-01-01

    Soap-free emulsion polymerization (SFEP) of methyl methacrylate, butyl acrylate was conducted in water/methanol media with sodium salts of four different acidic comonomers, namely styrene sulfonic acid (NaSS), 2-acrylamide-2-methyl-1-propane sulfonic acid (NaAmps), acrylic acid (NaAA), and itaconic acid (Na2ita). It was found that the introduction of methanol as co-solvent (35 wt%) to the medium greatly decreases the amount of water-soluble polyelectrolyte in the cases NaAA and Na2ita while it does not make difference for NaSS and NaAmps. Having employed the concept of conductance dependency to the ion mobility, the onset concentration in which soluble chains were formed was detected. The addition of sulfonic-based comonomers (NaSS and NaAmps), first decreased particle size and then led to predomination of solution polymerization over SFEP. On the contrary, the incorporation of carboxylic-based comonomers (NaAA and Na2ita) led to increase in particle size. Moreover, the particle size results were in good qualitative agreement with the classical Smith-Ewart theory.

  13. Tetrahedral boron in naturally occurring tourmaline

    SciTech Connect

    Tagg, S.L.; Cho, H.; Dyar, M.D.; Grew, E.S.

    1999-09-01

    Evidence for boron in both trigonal and tetrahedral coordination has been found in {sup 11}B magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) spectra of natural, inclusion-free specimens of aluminum-rich lithian tourmaline from granitic pregmatites.

  14. Resolvability and the Tetrahedral Configuration of Carbon.

    ERIC Educational Resources Information Center

    Kauffman, George B.

    1983-01-01

    Discusses evidence for the tetrahedral configuration of the carbon atom, indicating that three symmetrical configurations are theoretically possible for coordination number four. Includes table indicating that resolvability of compounds of type CR'R"R"'R"" is a necessary but not sufficient condition for proving tetrahedral…

  15. Preparation of strong anion-exchange chromatographic packings based on monodisperse polymeric beads and their application in the separation of biopolymers.

    PubMed

    Gong, Bolin; Li, Long; Zhu, Jinxia

    2005-08-01

    A new hydrophilic strong anion-exchange (SAX) stationary phase for HPLC has been synthesized by chemical modification of macroporous 8.0-microm monodisperse poly(glycidylmethacrylate-co-ethylenedimethacrylate) beads (P(GMA/EDMA)). The stationary phase was evaluated in detail to determine its ion-exchange properties, separability, reproducibility, hydrophilicity, and the effect of column loading and pH on the separation and retention of proteins. It was found to have an ion-exchange chromatographic (IEC) retention mechanism. The highest dynamic protein loading capacity of the synthesized SAX packing for BSA was 22.6 mg g(-1). Five proteins were separated within 6.0 min using the synthesized SAX resin. The SAX resin was also used for rapid separation and purification of recombinant human stem cell factor (rhSCF) from a crude extract solution in only one step. The purity of the purified of rhSCF was >92.4%.

  16. Search for Tetrahedral Symmetry in 70Ge

    NASA Astrophysics Data System (ADS)

    Le, Khanh; Haring-Kaye, R. A.; Elder, R. M.; Jones, K. D.; Morrow, S. I.; Tabor, S. L.; Tripathi, V.; Bender, P. C.; Allegro, P. R. P.; Medina, N. H.; Oliveira, J. R. B.; Doring, J.

    2014-09-01

    The even-even Ge isotopes have recently become an active testing ground for a variety of exotic structural characteristics, including the existence of tetrahedral symmetry (pyramid-like shapes). Although theoretical shape calculations predict the onset of tetrahedral symmetry near 72Ge, the experimental signatures (including vanishing quadrupole moments within high-spin bands) remain elusive. This study searched for possible experimental evidence of tetrahedral symmetry in 70Ge. Excited states in 70Ge were populated at Florida State University using the 55Mn(18O,p2n) fusion-evaporation reaction at 50 MeV. Prompt γ- γ coincidences were measured with a Compton-suppressed Ge array consisting of three Clover detectors and seven single-crystal detectors. The existing level scheme was enhanced through the addition of 20 new transitions and the rearrangement of five others based on the measured coincidence relations and relative intensities. Lifetimes of 24 states were measured using the Doppler-shift attenuation method, from which transition quadrupole moments were inferred. These results will be compared with those obtained from cranked Woods-Saxon calculations. The even-even Ge isotopes have recently become an active testing ground for a variety of exotic structural characteristics, including the existence of tetrahedral symmetry (pyramid-like shapes). Although theoretical shape calculations predict the onset of tetrahedral symmetry near 72Ge, the experimental signatures (including vanishing quadrupole moments within high-spin bands) remain elusive. This study searched for possible experimental evidence of tetrahedral symmetry in 70Ge. Excited states in 70Ge were populated at Florida State University using the 55Mn(18O,p2n) fusion-evaporation reaction at 50 MeV. Prompt γ- γ coincidences were measured with a Compton-suppressed Ge array consisting of three Clover detectors and seven single-crystal detectors. The existing level scheme was enhanced through the addition

  17. Algebraic cluster model with tetrahedral symmetry

    SciTech Connect

    Bijker, Roelof

    2010-12-23

    We propose an algebraic treatment of a four-body system in terms of a U(10) spectrum generating algebra. The formalism for the case of four identical objects is developed in detail. This includes a discussion of the permutation symmetry, a study of special solutions which are shown to correspond to the harmonic oscillator, the deformed oscillator and the spherical top with tetrahedral symmetry.

  18. Understanding tetrahedral liquids through patchy colloids.

    PubMed

    Saika-Voivod, Ivan; Smallenburg, Frank; Sciortino, Francesco

    2013-12-21

    We investigate the structural properties of a simple model for tetrahedral patchy colloids in which the patch width and the patch range can be tuned independently. For wide bond angles, a fully bonded network can be generated by standard Monte Carlo or molecular dynamics simulations of the model, providing a good method for generating defect-free random tetrahedral networks. This offers the possibility of focusing on the role of the patch angular width on the structure of the fully bonded network. The analysis of the fully bonded configurations as a function of the bonding angle shows how the bonding angle controls the system compressibility, the strength of the pre-peak in the structure factor, and ring size distribution. Comparison with models of liquid water and silica allows us to find the best mapping between these continuous potentials and the colloidal one. Building on previous studies focused on the connection between angular range and crystallization, the mapping makes it possible to shed new light on the glass-forming ability of network-forming tetrahedral liquids.

  19. Tetrahedral DNA nanostructure-based microRNA biosensor coupled with catalytic recycling of the analyte.

    PubMed

    Miao, Peng; Wang, Bidou; Chen, Xifeng; Li, Xiaoxi; Tang, Yuguo

    2015-03-25

    MicroRNAs are not only important regulators of a wide range of cellular processes but are also identified as promising disease biomarkers. Due to the low contents in serum, microRNAs are always difficult to detect accurately . In this study, an electrochemical biosensor for ultrasensitive detection of microRNA based on tetrahedral DNA nanostructure is developed. Four DNA single strands are engineered to form a tetrahedral nanostructure with a pendant stem-loop and modified on a gold electrode surface, which largely enhances the molecular recognition efficiency. Moreover, taking advantage of strand displacement polymerization, catalytic recycling of microRNA, and silver nanoparticle-based solid-state Ag/AgCl reaction, the proposed biosensor exhibits high sensitivity with the limit of detection down to 0.4 fM. This biosensor shows great clinical value and may have practical utility in early diagnosis and prognosis of certain diseases.

  20. Polymerization Initiated at the Sidewalls of Carbon Nanotubes

    NASA Technical Reports Server (NTRS)

    Tour, James M.; Hudson, Jared L.

    2011-01-01

    A process has been developed for growing polymer chains via anionic, cationic, or radical polymerization from the side walls of functionalized carbon nanotubes, which will facilitate greater dispersion in polymer matrices, and will greatly enhance reinforcement ability in polymeric material.

  1. Be3(AsO4)2 2H2O, a New Berylloarsenate Phase Containing Bridged Tetrahedral 3-Rings

    DTIC Science & Technology

    1994-04-15

    CsH(ZnPO 4 )2 and NaH(ZnPO 4 )2 contain "bridged" 3-rings as part of anionic layers sandwiching cesium and sodium cations (9). Finally, the novel...0 have been found in the layered, anionic zincophosphate phases CsH(ZnPO 4 )2 and NaH(ZnP0 4 )2 (9). However, the precise nature of the tetrahedral

  2. Extreme Mobility: Next Generation Tetrahedral Rovers

    NASA Astrophysics Data System (ADS)

    Clark, P. E.; Curtis, S. A.; Rilee, M. L.; Cheung, C. Y.; Wesenberg, R.; Brown, G.; Cooperrider, C.

    2007-01-01

    This paper describes the development and testing of a patented rover concept called Tetrahedral Explorer Technologies (TET), designed to provide extreme mobility and plug-and-play utility through reconfigurable addressable architecture. Here, we present the results of preliminary lab and field tests of Prototype III. Reconfigurable architecture is essential in exploration because reaching features of the great potential interest will require crossing a wide range of terrains largely inaccessible to permanently appendaged vehicles. One surface might be relatively flat and navigable, while another could be rough, variably sloping, broken, or dominated by unconsolidated debris. To be totally functional, structures must form pseudo-appendages varying in size, rate, and manner of deployment (gait) and moving at a speed approaching that of a human in rugged terrain. TET architecture is based on the tetrahedron, the basic space-filling shape, as building block. Tetrahedra are interconnected, their apices acting as nodes from which struts reversibly deploy. The tetrahedral framework acts as a simple skeletal muscular structure. Two simple robotic walker prototypes have already been developed from a single reconfigurable tetrahedron capable of tumbling. This paper presents the results of our attempts to simulate motions, improve the hardware, and develop gaits for a more evolved 12Tetrahedral Walker (Prototype 3) which high degrees of freedom locomotion commandable through a user friendly interface. Our rover is an early level mission concept, realized as an electromechanical system at present, which would allow autonomous in situ exploration of lunar sites when we return to the Moon. Such a rover could carry into inaccessible terrain an in situ analysis payload designed to provide not only details of composition of traversed terrain, but the identification of sites with resources useful for permanent bases, including water and high Ti glass.

  3. Dark Matter from Binary Tetrahedral Flavor Symmetry

    NASA Astrophysics Data System (ADS)

    Eby, David; Frampton, Paul

    2012-03-01

    Binary Tetrahedral Flavor Symmetry, originally developed as a quark family symmetry and later adapted to leptons, has proved both resilient and versatile over the past decade. In 2008 a minimal T' model was developed to accommodate quark and lepton masses and mixings using a family symmetry of (T'xZ2). We examine an expansion of this earlier model using an additional Z2 group that facilitates predictions of WIMP dark matter, the Cabibbo angle, and deviations from Tribimaximal Mixing, while giving hints at the nature of leptogenesis.

  4. Measure of disorder in tetrahedrally bonded semiconductors

    SciTech Connect

    Sundari, S. Tripura; Raghavan, G.

    2005-06-13

    A measure of crystalline order in tetrahedrally bonded semiconductors is proposed based on optical response. This measure is obtained from the <111> critical point structure in the dielectric spectra. This descriptor is sensitive to the nature and extent of disorder in specimens and distinguishes differences in medium and short-order present in amorphous materials. Application to Ar{sup +}-irradiated Si specimens yields the threshold amorphization dose and this technique is sensitive to structural changes which occur as a function of irradiation fluence both above and beyond the amorphization threshhold. Systematic variations are also obtained in hydrogenated amorphous-Si. The general validity of the method is indicated.

  5. Analysis of metal cations and inorganic anions in olive oil mill waste waters by atomic absorption spectroscopy and ion chromatography. Detection of metals bound mainly to the organic polymeric fraction.

    PubMed

    Arienzo, M; Capasso, R

    2000-04-01

    Metal cations were quantitatively detected by atomic absorption spectrometry in samples of olive oil mill waste waters obtained by a pressure process (omww(1)) (K, 17.1; Mg, 2.72; Ca, 2.24; Na, 0.40; Fe, 0.123; Zn, 0.0630; Mn, 0.0147; Cu, 0.00860 g L(-)(1)) and a centrifugation process (omww(2)) (K, 9.80; Mg, 1.65; Ca, 1.35; Na, 0. 162; Fe, 0.0330; Zn, 0.0301; Mn, 0.00910; Cu, 0.00980 g L(-)(1)). The inorganic anions, determined in the same samples by ion chromatography, proved to be Cl(-), H(2)PO(4)(-), F(-), SO(4)(2)(-), and NO(3)(-) (1.61, 1.05, 0.66, 0.52, and 0.023 g L(-)(1), respectively, in omww(1) and 0.61, 0.40, 0.25, 0.20, and 0.0090 g L(-)(1), respectively, in omww(2)). Most of the metal cations were revealed to be bound to the omww organic polymeric fraction (opf), composed of polysaccharides, phenol polymers, and proteins. Opf relative molecular weight was substantially estimated in the range between 1000 and 30000 Da for approximately 75% and in the range from 30000 to 100000 Da for approximately 25%. The free residual cations pool proved to be neutralized by the inorganic counteranions. Finally, the possible exploitation of this material in agriculture and in environmental biotechnology processes is also discussed in the light of its chemical and biochemical oxygen demand parameters.

  6. Polymerization as a Model Chain Reaction

    ERIC Educational Resources Information Center

    Morton, Maurice

    1973-01-01

    Describes the features of the free radical, anionic, and cationic mechanisms of chain addition polymerization. Indicates that the nature of chain reactions can be best taught through the study of macromolecules. (CC)

  7. Polymerization as a Model Chain Reaction

    ERIC Educational Resources Information Center

    Morton, Maurice

    1973-01-01

    Describes the features of the free radical, anionic, and cationic mechanisms of chain addition polymerization. Indicates that the nature of chain reactions can be best taught through the study of macromolecules. (CC)

  8. Raman Spectroscopic Studies of the High Pressure Behavior of Network Forming Tetrahedral Oxide Glasses.

    NASA Astrophysics Data System (ADS)

    Durben, Daniel John

    The ambient temperature structural and vibrational properties of a series of network forming tetrahedral oxide glasses have been investigated as a function of pressure with Raman spectroscopy. Glass samples were chosen to examine a range of network structures, from the fully polymerized GeO_2, to the partially depolymerized alkali tetrasilicates and disilicates, to the fully depolymerized forsterite. The Raman data suggest that fully polymerized oxide glass structures undergo network cation coordination changes in response to extreme compression through the involvement of bridging oxygens, without requiring bond breaking reactions. Spectral changes observed in partially depolymerized network glass structures are consistent with an increase in Si coordination during compression at the expense of nonbridging oxygens. The pressure range over which the coordination change occurs appears to be controlled by the size and concentration of alkali cations in the structure and depends on a balance between the competing beta-state conversion mechanism at low alkali content and steric considerations at higher alkali content. High pressure structural changes are largely reversible upon decompression, albeit with a large hysteresis. However, the spectra suggest that the breakup of the high coordinated network during the backtransformation to tetrahedral Si coordination occurs without a memory of the original Q -speciation or Si-O ring distribution. Thus, the backtransformation to low coordinated species upon decompression, occurring while the glass is compacted, favors a redistribution of Q-species and ring statistics relative to the original ambient structure.

  9. Details of tetrahedral anisotropic mesh adaptation

    NASA Astrophysics Data System (ADS)

    Jensen, Kristian Ejlebjerg; Gorman, Gerard

    2016-04-01

    We have implemented tetrahedral anisotropic mesh adaptation using the local operations of coarsening, swapping, refinement and smoothing in MATLAB without the use of any for- N loops, i.e. the script is fully vectorised. In the process of doing so, we have made three observations related to details of the implementation: 1. restricting refinement to a single edge split per element not only simplifies the code, it also improves mesh quality, 2. face to edge swapping is unnecessary, and 3. optimising for the Vassilevski functional tends to give a little higher value for the mean condition number functional than optimising for the condition number functional directly. These observations have been made for a uniform and a radial shock metric field, both starting from a structured mesh in a cube. Finally, we compare two coarsening techniques and demonstrate the importance of applying smoothing in the mesh adaptation loop. The results pertain to a unit cube geometry, but we also show the effect of corners and edges by applying the implementation in a spherical geometry.

  10. Streaming Compression of Tetrahedral Volume Meshes

    SciTech Connect

    Isenburg, M; Lindstrom, P; Gumhold, S; Shewchuk, J

    2005-11-21

    Geometry processing algorithms have traditionally assumed that the input data is entirely in main memory and available for random access. This assumption does not scale to large data sets, as exhausting the physical memory typically leads to IO-inefficient thrashing. Recent works advocate processing geometry in a 'streaming' manner, where computation and output begin as soon as possible. Streaming is suitable for tasks that require only local neighbor information and batch process an entire data set. We describe a streaming compression scheme for tetrahedral volume meshes that encodes vertices and tetrahedra in the order they are written. To keep the memory footprint low, the compressor is informed when vertices are referenced for the last time (i.e. are finalized). The compression achieved depends on how coherent the input order is and how many tetrahedra are buffered for local reordering. For reasonably coherent orderings and a buffer of 10,000 tetrahedra, we achieve compression rates that are only 25 to 40 percent above the state-of-the-art, while requiring drastically less memory resources and less than half the processing time.

  11. More About the Tetrahedral Unstructured Software System

    NASA Technical Reports Server (NTRS)

    Abdol-Hamid, Khaled S.; Frink, Neal T.; Hunter, Craig A.; Parikh, Paresh C.; Pizadeh, Shalyar Z.; Samareh, Jamshid A.; Bhat, Maharaj K.; Pandya, Mohagna J.; Grismer, Matthew J.

    2006-01-01

    TetrUSS is a comprehensive suite of computational fluid dynamics (CFD) programs that won the Software of the Year award in 1996 and has found increasing use in government, academia, and industry for solving realistic flow problems (especially in aerodynamics and aeroelastics of aircraft having complex shapes). TetrUSS includes not only programs for solving basic equations of flow but also programs that afford capabilities for efficient generation and utilization of computational grids and for graphical representation of computed flows (see figure). The 2004 version of the Tetrahedral Unstructured Software System (TetrUSS), which is one of two software systems reported in "NASA s 2004 Software of the Year," NASA Tech Briefs, Vol. 28, No. 10 (October 2004), page 18, has been improved greatly since 1996. These improvements include (1) capabilities to simulate viscous flow by solving the Navier-Stokes equations on unstructured grids, (2) portability to personal computers from diverse manufacturers, (3) advanced models of turbulence, (4) a parallel-processing version of one of the unstructured-grid Navier-Stokes-equation-solving programs, and (5) advanced programs for generating unstructured grids.

  12. Computer model of tetrahedral amorphous diamond

    NASA Astrophysics Data System (ADS)

    Djordjević, B. R.; Thorpe, M. F.; Wooten, F.

    1995-08-01

    We computer generate a model of amorphous diamond using the Wooten-Weaire method, with fourfold coordination everywhere. We investigate two models: one where four-membered rings are allowed and the other where the four-membered rings are forbidden; each model consisting of 4096 atoms. Starting from the perfect diamond crystalline structure, we first randomize the structure by introducing disorder through random bond switches at a sufficiently high temperature. Subsequently, the temperature is reduced in stages, and the topological and geometrical relaxation of the structure takes place using the Keating potential. After a long annealing process, a random network of comparatively low energy is obtained. We calculate the pair distribution function, mean bond angle, rms angular deviation, rms bond length, rms bond-length deviation, and ring statistics for the final relaxed structures. We minimize the total strain energy by adjusting the density of the sample. We compare our results with similar computer-generated models for amorphous silicon, and with experimental measurement of the structure factor for (predominantly tetrahedral) amorphous carbon.

  13. Hoop/column and tetrahedral truss electromagnetic tests

    NASA Technical Reports Server (NTRS)

    Bailey, M. C.

    1987-01-01

    The distortion of antennas was measured with a metric camera system at discrete target locations on the surface. Given are surface distortion for hoop column reflector antennas, for tetrahedral truss reflector antennas, and distortion contours for the tetrahedral truss reflector. Radiation patterns at 2.27-GHz, 4.26-GHz, 7.73-GHz and 11.6-GHz are given for the hoop column antenna. Also given are radiation patterns at 4.26-GHz and 7.73-GHz for the tetrahedral truss antenna.

  14. Polymeric microspheres

    DOEpatents

    Walt, David R.; Mandal, Tarun K.; Fleming, Michael S.

    2004-04-13

    The invention features core-shell microsphere compositions, hollow polymeric microspheres, and methods for making the microspheres. The microspheres are characterized as having a polymeric shell with consistent shell thickness.

  15. Highly Porous Zirconium Metal–Organic Frameworks with β-UH 3 -like Topology Based on Elongated Tetrahedral Linkers

    SciTech Connect

    Zhang, Xin; Zhang, Xu; Johnson, Jacob A.; Chen, Yu-Sheng; Zhang, Jian

    2016-06-24

    Two non-interpenetrated zirconium metal–organic frameworks (Zr-MOFs), NPF-200 and NPF-201, were synthesized via the assembly of elongated tetrahedral linkers with Zr6 and Zr8 clusters. They represent the first examples of MOFs to have the β-UH3-like, 4,12,12T1 topology. Upon activation, NPF-200 exhibits the largest BET surface area (5463 m2 g–1) and void volume (81.6%) among all MOFs formed from tetrahedral ligands. Composed of negative-charged boron-centered tetrahedral linkers, NPF-201 is an anionic Zr-MOF which selectively uptakes photoactive [Ru(bpy)3]2+ for heterogeneous photo-oxidation of thioanisole.

  16. Tetrahedral and Hexahedral Mesh Adaptation for CFD Problems

    NASA Technical Reports Server (NTRS)

    Biswas, Rupak; Strawn, Roger C.; Chancellor, Marisa K. (Technical Monitor)

    1997-01-01

    This paper presents two unstructured mesh adaptation schemes for problems in computational fluid dynamics. The procedures allow localized grid refinement and coarsening to efficiently capture aerodynamic flow features of interest. The first procedure is for purely tetrahedral grids; unfortunately, repeated anisotropic adaptation may significantly deteriorate the quality of the mesh. Hexahedral elements, on the other hand, can be subdivided anisotropically without mesh quality problems. Furthermore, hexahedral meshes yield more accurate solutions than their tetrahedral counterparts for the same number of edges. Both the tetrahedral and hexahedral mesh adaptation procedures use edge-based data structures that facilitate efficient subdivision by allowing individual edges to be marked for refinement or coarsening. However, for hexahedral adaptation, pyramids, prisms, and tetrahedra are used as buffer elements between refined and unrefined regions to eliminate hanging vertices. Computational results indicate that the hexahedral adaptation procedure is a viable alternative to adaptive tetrahedral schemes.

  17. Tetrahedral and Hexahedral Mesh Adaptation for CFD Problems

    NASA Technical Reports Server (NTRS)

    Biswas, Rupak; Strawn, Roger C.; Chancellor, Marisa K. (Technical Monitor)

    1997-01-01

    This paper presents two unstructured mesh adaptation schemes for problems in computational fluid dynamics. The procedures allow localized grid refinement and coarsening to efficiently capture aerodynamic flow features of interest. The first procedure is for purely tetrahedral grids; unfortunately, repeated anisotropic adaptation may significantly deteriorate the quality of the mesh. Hexahedral elements, on the other hand, can be subdivided anisotropically without mesh quality problems. Furthermore, hexahedral meshes yield more accurate solutions than their tetrahedral counterparts for the same number of edges. Both the tetrahedral and hexahedral mesh adaptation procedures use edge-based data structures that facilitate efficient subdivision by allowing individual edges to be marked for refinement or coarsening. However, for hexahedral adaptation, pyramids, prisms, and tetrahedra are used as buffer elements between refined and unrefined regions to eliminate hanging vertices. Computational results indicate that the hexahedral adaptation procedure is a viable alternative to adaptive tetrahedral schemes.

  18. Polymers for anion recognition and sensing.

    PubMed

    Rostami, Ali; Taylor, Mark S

    2012-01-16

    In biological systems, the selective and high-affinity recognition of anionic species is accomplished by macromolecular hosts (anion-binding proteins) that have been "optimized" through evolution. Surprisingly, it is only recently that chemists have systematically attempted to develop anion-responsive synthetic macromolecules for potential applications in medicine, national security, or environmental monitoring. Recent results indicating that unique features of polymeric systems such as signal amplification, multivalency, and cooperative behavior may be exploited productively in the context of anion recognition and sensing are documented. The wide variety of interactions-including Lewis acid/base, ion-pairing, and hydrogen bonding-that have been employed for this purpose is reflected in the structural diversity of anion-responsive macromolecules identified to date.

  19. Covalent Polymers Containing Discrete Heterocyclic Anion Receptors

    PubMed Central

    Rambo, Brett M.; Silver, Eric S.; Bielawski, Christopher W.; Sessler, Jonathan L.

    2010-01-01

    This chapter covers recent advances in the development of polymeric materials containing discrete heterocyclic anion receptors, and focuses on advances in anion binding and chemosensor chemistry. The development of polymers specific for anionic species is a relatively new and flourishing area of materials chemistry. The incorporation of heterocyclic receptors capable of complexing anions through non-covalent interactions (e.g., hydrogen bonding and electrostatic interactions) provides a route to not only sensitive but also selective polymer materials. Furthermore, these systems have been utilized in the development of polymers capable of extracting anionic species from aqueous environments. These latter materials may lead to advances in water purification and treatment of diseases resulting from surplus ions. PMID:20871791

  20. Anion permselective membrane

    NASA Technical Reports Server (NTRS)

    Hodgdon, R. B.; Waite, W. A.

    1982-01-01

    The synthesis and fabrication of polymeric anion permselective membranes for redox systems are discussed. Variations of the prime candidate anion membrane formulation to achieve better resistance and/or lower permeability were explored. Processing parameters were evaluated to lower cost and fabricate larger sizes. The processing techniques to produce more membranes per batch were successfully integrated with the fabrication of larger membranes. Membranes of about 107 cm x 51 cm were made in excellent yield. Several measurements were made on the larger sample membranes. Among the data developed were water transport and transference numbers for these prime candidate membranes at 20 C. Other work done on this system included characterization of a number of specimens of candidate membranes which had been returned after service lives of up to sixteen months. Work with new polymer constituents, with new N.P.'s, catalysts and backing fabrics is discussed. Some work was also done to evaluate other proportions of the ingredients of the prime candidate system. The adoption of a flow selectivity test at elevated temperature was explored.

  1. Tetrahedral oxyanions-assisted supramolecular assemblies of pyridine-based tectons into hydrogen-bonding networks

    NASA Astrophysics Data System (ADS)

    Ding, Xue-Hua; Wang, Shi; Li, Yong-Hua; Huang, Wei

    2015-01-01

    The systematic research has been done into structural variations of supramolecular architectures by the self assembly of two pyridine-based potential anion receptors, 1-(4-pyridyl)piperazine (L1) and 4-pyrrolidinopyridine (L2), and different inorganic acids (HCl, HBr, HI, HNO3, HClO4, HIO4, H2SO4 and H3PO4). The formation of four fascinating salts, i.e. (H2L12+)·(H2PO4-)2 (1), (H2L12+)·(ClO4-)2 (2), (HL2+)·(ClO4-) (3) and (HL2+)·(IO4-) (4), indicates that N-heterocyclic L1 and L2 are prone to cocrystallize with tetrahedral oxyanions and anionic topologies play a crucial role in the crystallization process. Structural analyses reveal that various intermolecular ring motifs have been generated by robust hydrogen-bonding interactions in compounds 1-4. In particular, interesting substructures were observed in H2PO4- from salts 1 due to its polytopic potential hydrogen-bonding donor and acceptor oxygen atoms, including ring motifs, 1D ribbons and 2D supramolecular framework. Much to our surprise, crystal 4 proves to be a member of few supramolecular salts crystallizing with IO4- anion according to the Cambridge Structure Database (CSD).

  2. Gas-phase acidities of tetrahedral oxyacids from ab initio electronic structure theory

    SciTech Connect

    Rustad, J.R.; Dixon, D.A.; Kubicki, J.D.; Felmy, A.R.

    2000-05-04

    Density functional calculations have been performed on several protonation states of the oxyacids of Si, P, V, As, Cr, and S. Structures and vibrational frequencies are in good agreement with experimental values where these are available. A reasonably well-defined correlation between the calculated gas-phase acidities and the measured pK{sub a} in aqueous solution has been found. The pK{sub a}/gas-phase acidity slopes are consistent with those derived from previous molecular mechanics calculations on ferric hydrolysis and the first two acidity constants for orthosilicic acid. The successive deprotonation of other H{sub n}TO{sub 4} species, for a given tetrahedral anion T are roughly consistent with this slope, but not to the extent that there is a universal correlation among all species.

  3. Living olefin polymerization processes

    DOEpatents

    Schrock, R.R.; Baumann, R.

    1999-03-30

    Processes for the living polymerization of olefin monomers with terminal carbon-carbon double bonds are disclosed. The processes employ initiators that include a metal atom and a ligand having two group 15 atoms and a group 16 atom or three group 15 atoms. The ligand is bonded to the metal atom through two anionic or covalent bonds and a dative bond. The initiators are particularly stable under reaction conditions in the absence of olefin monomer. The processes provide polymers having low polydispersities, especially block copolymers having low polydispersities. It is an additional advantage of these processes that, during block copolymer synthesis, a relatively small amount of homopolymer is formed.

  4. Living olefin polymerization processes

    DOEpatents

    Schrock, Richard R.; Baumann, Robert

    1999-01-01

    Processes for the living polymerization of olefin monomers with terminal carbon-carbon double bonds are disclosed. The processes employ initiators that include a metal atom and a ligand having two group 15 atoms and a group 16 atom or three group 15 atoms. The ligand is bonded to the metal atom through two anionic or covalent bonds and a dative bond. The initiators are particularly stable under reaction conditions in the absence of olefin monomer. The processes provide polymers having low polydispersities, especially block copolymers having low polydispersities. It is an additional advantage of these processes that, during block copolymer synthesis, a relatively small amount of homopolymer is formed.

  5. Living olefin polymerization processes

    DOEpatents

    Schrock, Richard R.; Baumann, Robert

    2003-08-26

    Processes for the living polymerization of olefin monomers with terminal carbon-carbon double bonds are disclosed. The processes employ initiators that include a metal atom and a ligand having two group 15 atoms and a group 16 atom or three group 15 atoms. The ligand is bonded to the metal atom through two anionic or covalent bonds and a dative bond. The initiators are particularly stable under reaction conditions in the absence of olefin monomer. The processes provide polymers having low polydispersities, especially block copolymers having low polydispersities. It is an additional advantage of these processes that, during block copolymer synthesis, a relatively small amount of homopolymer is formed.

  6. Living olefin polymerization processes

    DOEpatents

    Schrock, Richard R.; Bauman, Robert

    2006-11-14

    Processes for the living polymerization of olefin monomers with terminal carbon-carbon double bonds are disclosed. The processes employ initiators that include a metal atom and a ligand having two group 15 atoms and a group 16 atom or three group 15 atoms. The ligand is bonded to the metal atom through two anionic or covalent bonds and a dative bond. The initiators are particularly stable under reaction conditions in the absence of olefin monomer. The processes provide polymers having low polydispersities, especially block copolymers having low polydispersities. It is an additional advantage of these processes that, during block copolymer synthesis, a relatively small amount of homopolymer is formed.

  7. Anion-π interactions involving [MX(n)](m-) anions: a comprehensive theoretical study.

    PubMed

    Estarellas, Carolina; Quiñonero, David; Deyà, Pere M; Frontera, Antonio

    2013-01-14

    In this manuscript we perform a systematic study on the geometric and energetic features of anion-π complexes, wherein the anion is a metal complex of variable shapes and charges. Such a study is lacking in the literature. For the calculations we used the ab initio RI-MP2/def2-TZVPP level of theory. A search in the Cambridge Structural Database (CSD) provides the experimental starting point that inspired the subsequent theoretical study. The influence of [MX(n)](m-) on the anion-π interaction was analyzed in terms of energetic, geometric, and charge transfer properties and Bader's theory of "atom-in-molecules" (AIM). The binding energy depends on the coordination index, geometric features and different orientations adopted by the metallic anion. The binding mode resembling a stacking interaction for linear, trigonal planar and square-planar anions is the most favorable. For tetrahedral and octahedral anions the most favorable orientation is the one with three halogen atoms pointing to the ring.

  8. Molecular origin of auxetic behavior in tetrahedral framework silicates.

    PubMed

    Alderson, Andrew; Evans, Kenneth E

    2002-11-25

    Recent analytical models for the Poisson's ratios (nu(ij)) of tetrahedral frameworks are applied to alpha-cristobalite and alpha-quartz for the first time. Rotation and dilation of the SiO4 tetrahedral subunits are considered. Each mechanism leads to negative nu(31) values, whereas negative and positive values are possible when they act concurrently. The concurrent model is in excellent agreement with experiment and explains the dichotomy between negative and positive nu(31) values in alpha-cristobalite and alpha-quartz, respectively. The predicted strain-dependent trends confirm those from molecular modeling.

  9. Lattice Cleaving: A Multimaterial Tetrahedral Meshing Algorithm with Guarantees

    PubMed Central

    Bronson, Jonathan; Levine, Joshua A.; Whitaker, Ross

    2014-01-01

    We introduce a new algorithm for generating tetrahedral meshes that conform to physical boundaries in volumetric domains consisting of multiple materials. The proposed method allows for an arbitrary number of materials, produces high-quality tetrahedral meshes with upper and lower bounds on dihedral angles, and guarantees geometric fidelity. Moreover, the method is combinatoric so its implementation enables rapid mesh construction. These meshes are structured in a way that also allows grading, to reduce element counts in regions of homogeneity. Additionally, we provide proofs showing that both element quality and geometric fidelity are bounded using this approach. PMID:24356365

  10. Indirect-drive radiation uniformity in tetrahedral hohlraums

    SciTech Connect

    Schnittman, J.D.; Craxton, R.S.

    1996-10-01

    Tetrahedral hohlraums, by which are understood spherical hohlraums with four laser entrance holes (LEH{close_quote}s) placed at or near the vertices of a tetrahedron, are proposed for the National Ignition Facility (NIF) [J. Lindl, Phys. Plasmas {bold 2}, 3933 (1995)] and the upgraded OMEGA laser [T. R. Boehly {ital et} {ital al}., Rev. Sci. Instrum. {bold 66}, 508 (1995)]. All but four of the 48 NIF beams can irradiate a tetrahedral hohlraum, assuming that 72 beam ports are provided to accommodate direct drive. On OMEGA, the target chamber provides an exact tetrahedral symmetry, permitting the irradiation of tetrahedral hohlraums with all 60 beams. Hohlraum designs are optimized using a new three-dimensional view-factor program called Buttercup, which traces all beam paths through the hohlraum and calculates the radiation flux on the capsule for different values of the albedo. Good irradiation uniformity ({approximately}2{percent} rms) can be obtained on the capsule at all times during the implosion, even with identical beam temporal histories, in contrast to the case of cylindrical hohlraums where {open_quote}{open_quote}beam phasing{close_quote}{close_quote} is needed. {copyright} {ital 1996 American Institute of Physics.}

  11. Indirect-drive radiation uniformity in tetrahedral hohlraums

    NASA Astrophysics Data System (ADS)

    Schnittman, J. D.; Craxton, R. S.

    1996-10-01

    Tetrahedral hohlraums, by which are understood spherical hohlraums with four laser entrance holes (LEH's) placed at or near the vertices of a tetrahedron, are proposed for the National Ignition Facility (NIF) [J. Lindl, Phys. Plasmas 2, 3933 (1995)] and the upgraded OMEGA laser [T. R. Boehly et al., Rev. Sci. Instrum. 66, 508 (1995)]. All but four of the 48 NIF beams can irradiate a tetrahedral hohlraum, assuming that 72 beam ports are provided to accommodate direct drive. On OMEGA, the target chamber provides an exact tetrahedral symmetry, permitting the irradiation of tetrahedral hohlraums with all 60 beams. Hohlraum designs are optimized using a new three-dimensional view-factor program called Buttercup, which traces all beam paths through the hohlraum and calculates the radiation flux on the capsule for different values of the albedo. Good irradiation uniformity (˜2% rms) can be obtained on the capsule at all times during the implosion, even with identical beam temporal histories, in contrast to the case of cylindrical hohlraums where ``beam phasing'' is needed.

  12. Hinge specification for a square-faceted tetrahedral truss

    NASA Technical Reports Server (NTRS)

    Adams, L. R.

    1984-01-01

    A square-faceted tetrahedral truss is geometrically analyzed. Expressions are developed for single degree of freedom hinges which allow packaging of the structure into a configuration in which all members are parallel and closely packed in a square pattern. Deployment is sequential, thus providing control over the structure during deployment.

  13. Tetrahedral Models of Learning: Application to College Reading.

    ERIC Educational Resources Information Center

    Nist, Sherrie L.

    J. D. Bransford's tetrahedral model of learning considers four variables: (1) learning activities, (2) characteristics of the learner, (3) criterial tasks, and (4) the nature of the materials. Bransford's model provides a research-based theoretical framework that can be used to teach, model, and have students apply a variety of study strategies to…

  14. The benzene radical anion: A computationally demanding prototype for aromatic anions

    SciTech Connect

    Bazante, Alexandre P. Bartlett, Rodney J.; Davidson, E. R.

    2015-05-28

    The benzene radical anion is studied with ab initio coupled-cluster theory in large basis sets. Unlike the usual assumption, we find that, at the level of theory investigated, the minimum energy geometry is non-planar with tetrahedral distortion at two opposite carbon atoms. The anion is well known for its instability to auto-ionization which poses computational challenges to determine its properties. Despite the importance of the benzene radical anion, the considerable attention it has received in the literature so far has failed to address the details of its structure and shape-resonance character at a high level of theory. Here, we examine the dynamic Jahn-Teller effect and its impact on the anion potential energy surface. We find that a minimum energy geometry of C{sub 2} symmetry is located below one D{sub 2h} stationary point on a C{sub 2h} pseudo-rotation surface. The applicability of standard wave function methods to an unbound anion is assessed with the stabilization method. The isotropic hyperfine splitting constants (A{sub iso}) are computed and compared to data obtained from experimental electron spin resonance experiments. Satisfactory agreement with experiment is obtained with coupled-cluster theory and large basis sets such as cc-pCVQZ.

  15. Is there tetrahedral Fe/sup 3 +/ in biotite

    SciTech Connect

    Dyar, M.D.; Burns, R.G.; Rossman, G.R.

    1985-01-01

    Tetrahedral Fe/sup 3 +/ has been observed in Moessbauer and optical studies of Al-deficient micas, including synthetic ferri-annites, annites from banded iron formations and phlogopites from deep-seated rocks. In such samples Si + Al < 4 (per 11 0), and 0.10-0.67 formula units of Fe/sup 3 +/ fill the tetrahedral sites in the structure. The authors also discovered several Al-rich biotites which contain small amounts of Fe/sub tet//sup 3 +/ based on their spectroscopic data. Fe/sup 3 +/ appears to be displacing some of the Al/sup 3 +/ into the octahedral site. Examination of the literature shows nine other cases of Fe/sub tet//sup 3 +/ in trioctahedral 1M micas where Si + Al > 4. Traditionally, the effects of cation substitutions on the physical properties have been considered to be dependent on the size difference between the octahedral and tetrahedral layers of the structure. Much attention has focused on the substitution of the larger Fe/sup 2 +/ for Mg/sup 2 +/ and other cations in the octahedra of relatively simple synthetic compositions. However, in the natural micas studied here high fO/sub 2/ and high proportions of Al/sup 3 +/, Fe/sup 3 +/, and Ti/sup 4 +/ in the compositions raise the issue of structural readjustments based on substitution of small cations into the structure. In our samples, the average octahedral cation size is 0.67 A. If many small octahedral cations are incorporated into the structure during biotite formation, considerable octahedral flattening and (in response) tetrahedral rotation must occur to stabilize the mica. Perhaps the high degree of tetrahedral rotation allows accommodation of the larger Fe/sub tet//sup 3 +/ instead of Al/sub tet//sup 3 +/.

  16. Sterically shielded diboron-containing metallocene olefin polymerization catalysts

    DOEpatents

    Marks, Tobin J.; Ja, Li; Yang, Xinmin

    1995-09-05

    A non-coordinating anion, preferably containing a sterically shielded diboron hydride, if combined with a cyclopenta-dienyl-substituted metallocene cation component, such as a zirconocene metallocene, is a useful olefin polymerization catalyst component. The anion preferably has the formula ##STR1## where R is branched lower alkyl, such as t-butyl.

  17. Diverse stereocontrol effects induced by weakly coordinating anions. Stereospecific olefin polymerization pathways at archetypal C(s)- and C(1)-symmetric metallocenium catalysts using mono- and polynuclear halo-perfluoroarylmetalates as cocatalysts.

    PubMed

    Roberts, John A S; Chen, Ming-Chou; Seyam, Afif M; Li, Liting; Zuccaccia, Cristiano; Stahl, Nicholas G; Marks, Tobin J

    2007-10-24

    Counteranion effects on propylene polymerization rates and stereoselectivities are compared using Cs-symmetric Me2C(Cp)(Flu)ZrMe2 (1; Cp = C5H4,eta5-cyclopentadienyl; Flu = C13H8, eta5-fluorenyl) and C1-symmetric Me2Si(OHF)(CpR*)ZrMe2 (2; OHF = C13H16, eta5-octahydrofluorenyl; CpR* = eta5-3-(-)-menthylcyclopentadienyl) precatalysts activated with the mononuclear and polynuclear perfluoroarylborate, -aluminate, and -gallate cocatalysts/activators B(C6F5)3 (3), B(o-C6F5C6F4)3 (4), Al(C6F5)3 (5), Ph3C+B(C6F5)4- (6) Ph3C+FAl(o-C6F5C6F4)3- (7), Ga(C6F5)3 (8), and recently reported mono- and polymetallic trityl perfluoroarylhalometalates Ph3C+FB(C6F5)3- (9), Ph3C+FB(o-C6F5C6F4)3- (10), (Ph3C+)xFx[Al(C6F5)3]yx- (x = 1, y = 1, 11; x = 1, y = 2, 12; x = 2, y = 3, 13), Ph3C+(C6F5)3AlFAl(o-C6F5C6F4)3- (14), Ph3C+XAl(C6F5)3- (X = Cl, 15; X = Br, 16), and Ph3C+F[Ga(C6F5)3]2- (17). Temperature, propylene concentration, and solvent polarity dependence are surveyed in polymerizations catalyzed by 1 activated with cocatalysts 3-16 and with a 1:2 ratio of Ph3CCl and 5, and with a 1:2 ratio of Ph3CBr and 5, and by 2 activated with 3, 6, 7, 12, and 14. Remarkable stereocontrol with high activities is observed for 1 + 12 and 1 + 14. Polypropylene samples produced using C1-symmetric precatalyst 2 are subjected to microstructural analyses using stochastic models describing the relative contributions of enantiofacial misinsertion and backskip processes. A powerful technique is introduced for calculating interparametric correlation matrices for these nonlinear stochastic models. The collected results significantly extend what is known about ion-pairing effects in the case of Cs-symmetric precatalyst 1 and allow these findings to be applied to the case of C1-symmetric precatalyst 2 as an agent of isospecific propylene polymerization.

  18. Single-laser, one beam, tetrahedral magneto-optical trap.

    PubMed

    Vangeleyn, Matthieu; Griffin, Paul F; Riis, Erling; Arnold, Aidan S

    2009-08-03

    We have realized a 4-beam pyramidal magneto-optical trap ideally suited for future microfabrication. Three mirrors split and steer a single incoming beam into a tripod of reflected beams, allowing trapping in the four-beam overlap volume. We discuss the influence of mirror angle on cooling and trapping, finding optimum efficiency in a tetrahedral configuration. We demonstrate the technique using an ex-vacuo mirror system to illustrate the previously inaccessible supra-plane pyramid MOT configuration. Unlike standard pyramidal MOTs both the pyramid apex and its mirror angle are non-critical and our MOT offers improved molasses free from atomic shadows in the laser beams. The MOT scheme naturally extends to a 2-beam refractive version with high optical access. For quantum gas experiments, the mirror system could also be used for a stable 3D tetrahedral optical lattice.

  19. Coarse-grained theory of a realistic tetrahedral liquid model

    NASA Astrophysics Data System (ADS)

    Procaccia, I.; Regev, I.

    2012-02-01

    Tetrahedral liquids such as water and silica-melt show unusual thermodynamic behavior such as a density maximum and an increase in specific heat when cooled to low temperatures. Previous work had shown that Monte Carlo and mean-field solutions of a lattice model can exhibit these anomalous properties with or without a phase transition, depending on the values of the different terms in the Hamiltonian. Here we use a somewhat different approach, where we start from a very popular empirical model of tetrahedral liquids —the Stillinger-Weber model— and construct a coarse-grained theory which directly quantifies the local structure of the liquid as a function of volume and temperature. We compare the theory to molecular-dynamics simulations and show that the theory can rationalize the simulation results and the anomalous behavior.

  20. A computational study of nodal-based tetrahedral element behavior.

    SciTech Connect

    Gullerud, Arne S.

    2010-09-01

    This report explores the behavior of nodal-based tetrahedral elements on six sample problems, and compares their solution to that of a corresponding hexahedral mesh. The problems demonstrate that while certain aspects of the solution field for the nodal-based tetrahedrons provide good quality results, the pressure field tends to be of poor quality. Results appear to be strongly affected by the connectivity of the tetrahedral elements. Simulations that rely on the pressure field, such as those which use material models that are dependent on the pressure (e.g. equation-of-state models), can generate erroneous results. Remeshing can also be strongly affected by these issues. The nodal-based test elements as they currently stand need to be used with caution to ensure that their numerical deficiencies do not adversely affect critical values of interest.

  1. Interactive isosurface ray tracing of time-varying tetrahedral volumes.

    PubMed

    Wald, Ingo; Friedrich, Heiko; Knoll, Aaron; Hansen, Charles D

    2007-01-01

    We describe a system for interactively rendering isosurfaces of tetrahedral finite-element scalar fields using coherent ray tracing techniques on the CPU. By employing state-of-the art methods in polygonal ray tracing, namely aggressive packet/frustum traversal of a bounding volume hierarchy, we can accomodate large and time-varying unstructured data. In conjunction with this efficiency structure, we introduce a novel technique for intersecting ray packets with tetrahedral primitives. Ray tracing is flexible, allowing for dynamic changes in isovalue and time step, visualization of multiple isosurfaces, shadows, and depth-peeling transparency effects. The resulting system offers the intuitive simplicity of isosurfacing, guaranteed-correct visual results, and ultimately a scalable, dynamic and consistently interactive solution for visualizing unstructured volumes.

  2. Quality Tetrahedral Mesh Smoothing via Boundary-Optimized Delaunay Triangulation.

    PubMed

    Gao, Zhanheng; Yu, Zeyun; Holst, Michael

    2012-12-01

    Despite its great success in improving the quality of a tetrahedral mesh, the original optimal Delaunay triangulation (ODT) is designed to move only inner vertices and thus cannot handle input meshes containing "bad" triangles on boundaries. In the current work, we present an integrated approach called boundary-optimized Delaunay triangulation (B-ODT) to smooth (improve) a tetrahedral mesh. In our method, both inner and boundary vertices are repositioned by analytically minimizing the error between a paraboloid function and its piecewise linear interpolation over the neighborhood of each vertex. In addition to the guaranteed volume-preserving property, the proposed algorithm can be readily adapted to preserve sharp features in the original mesh. A number of experiments are included to demonstrate the performance of our method.

  3. Polymeric nanoparticles

    PubMed Central

    Bolhassani, Azam; Javanzad, Shabnam; Saleh, Tayebeh; Hashemi, Mehrdad; Aghasadeghi, Mohammad Reza; Sadat, Seyed Mehdi

    2014-01-01

    Nanocarriers with various compositions and biological properties have been extensively applied for in vitro/in vivo drug and gene delivery. The family of nanocarriers includes polymeric nanoparticles, lipid-based carriers (liposomes/micelles), dendrimers, carbon nanotubes, and gold nanoparticles (nanoshells/nanocages). Among different delivery systems, polymeric carriers have several properties such as: easy to synthesize, inexpensive, biocompatible, biodegradable, non-immunogenic, non-toxic, and water soluble. In addition, cationic polymers seem to produce more stable complexes led to a more protection during cellular trafficking than cationic lipids. Nanoparticles often show significant adjuvant effects in vaccine delivery since they may be easily taken up by antigen presenting cells (APCs). Natural polymers such as polysaccharides and synthetic polymers have demonstrated great potential to form vaccine nanoparticles. The development of new adjuvants or delivery systems for DNA and protein immunization is an expanding research field. This review describes polymeric carriers especially PLGA, chitosan, and PEI as vaccine delivery systems. PMID:24128651

  4. Motion compensation for PET image reconstruction using deformable tetrahedral meshes

    NASA Astrophysics Data System (ADS)

    Manescu, P.; Ladjal, H.; Azencot, J.; Beuve, M.; Shariat, B.

    2015-12-01

    Respiratory-induced organ motion is a technical challenge to PET imaging. This motion induces displacements and deformation of the organs tissues, which need to be taken into account when reconstructing the spatial radiation activity. Classical image-based methods that describe motion using deformable image registration (DIR) algorithms cannot fully take into account the non-reproducibility of the respiratory internal organ motion nor the tissue volume variations that occur during breathing. In order to overcome these limitations, various biomechanical models of the respiratory system have been developed in the past decade as an alternative to DIR approaches. In this paper, we describe a new method of correcting motion artefacts in PET image reconstruction adapted to motion estimation models such as those based on the finite element method. In contrast with the DIR-based approaches, the radiation activity was reconstructed on deforming tetrahedral meshes. For this, we have re-formulated the tomographic reconstruction problem by introducing a time-dependent system matrix based calculated using tetrahedral meshes instead of voxelized images. The MLEM algorithm was chosen as the reconstruction method. The simulations performed in this study show that the motion compensated reconstruction based on tetrahedral deformable meshes has the capability to correct motion artefacts. Results demonstrate that, in the case of complex deformations, when large volume variations occur, the developed tetrahedral based method is more appropriate than the classical DIR-based one. This method can be used, together with biomechanical models controlled by external surrogates, to correct motion artefacts in PET images and thus reducing the need for additional internal imaging during the acquisition.

  5. Mesh quality control for multiply-refined tetrahedral grids

    NASA Technical Reports Server (NTRS)

    Biswas, Rupak; Strawn, Roger

    1994-01-01

    A new algorithm for controlling the quality of multiply-refined tetrahedral meshes is presented in this paper. The basic dynamic mesh adaption procedure allows localized grid refinement and coarsening to efficiently capture aerodynamic flow features in computational fluid dynamics problems; however, repeated application of the procedure may significantly deteriorate the quality of the mesh. Results presented show the effectiveness of this mesh quality algorithm and its potential in the area of helicopter aerodynamics and acoustics.

  6. A Trivariate Clough-Tocher Scheme for Tetrahedral Data.

    DTIC Science & Technology

    1984-06-01

    data, for arbitrary m and in arbitrarily many variables. However, all of the existing tetrahedral schemes yield rational interpolants . One would like...from the cardinal properties of barycentric coordinates that =bk 6 5 _ bki (2.3) where 6 is the Kronecker delta. The piecewise cubic interpolant (on a...1984 Abstract -An interpolation scheme is described for values of position, gradient and Hessian at scattered points in three variables. The domain is

  7. Synthesis and the crystal and molecular structure of the silver(I)-germanium(IV) polymeric complex with citrate anions {[Ag2Ge(H Cit)2(H2O)2] • 2H2O} n

    NASA Astrophysics Data System (ADS)

    Sergienko, V. S.; Martsinko, E. E.; Seifullina, I. I.; Churakov, A. V.; Chebanenko, E. A.

    2016-03-01

    The synthesis and X-ray diffraction study of compound {[Ag2Ge(H Cit)2(H2O)2] • 2H2O} n , where H4 Cit is the citric acid, are performed. In the polymeric structure, the H Cit 3- ligand fulfils the tetradentate chelate-μ4-bridging (3Ag, Ge) function (tridentate with respect to Ge and Ag atoms). The Ge atom is octahedrally coordinated by six O atoms of two H Cit 3-ligands. The coordination polyhedron of the Ag atom is an irregular five-vertex polyhedron [four O atoms of four H Cit 3- ligands and the O(H2O) atom]. An extended system of O-H···O hydrogen bonds connects complex molecules into a supramolecular 3D-framework.

  8. Nucleation barriers in tetrahedral liquids spanning glassy and crystallizing regimes.

    PubMed

    Saika-Voivod, Ivan; Romano, Flavio; Sciortino, Francesco

    2011-09-28

    Crystallization and vitrification of tetrahedral liquids are important both from a fundamental and a technological point of view. Here, we study via extensive umbrella sampling Monte Carlo computer simulations the nucleation barriers for a simple model for tetrahedral patchy particles in the regime where open tetrahedral crystal structures (namely, cubic and hexagonal diamond and their stacking hybrids) are thermodynamically stable. We show that by changing the angular bond width, it is possible to move from a glass-forming model to a readily crystallizing model. From the shape of the barrier we infer the role of surface tension in the formation of the crystalline clusters. Studying the trends of the nucleation barriers with the temperature and the patch width, we are able to identify an optimal value of the patch size that leads to easy nucleation. Finally, we find that the nucleation barrier is the same, within our numerical precision, for both diamond crystals and for their stacking forms. © 2011 American Institute of Physics

  9. Detection and accumulation of tetrahedral intermediates in elastase catalysis.

    PubMed Central

    Fink, A L; Meehan, P

    1979-01-01

    Tetrahedral intermediates in the reaction of elastase with specific di- and tripeptide p-nitroanilide substrates have been detected, accumulated, and stabilized at high pH by using subzero temperatures and fluid aqueous/organic cryosolvents. The tetrahedral adducts are characterized by spectra with lambda max of 359 +/- 2 nm, compared with thata of 380 nm for p-nitroaniline and 315-320 nm for the substrates. The maximal concentration of intermediate that could be accumulated varied with the different substrates from 40 to 100% of the active enzyme present. The pH dependence of the reactions indicated that formation of the tetrahedral intermediates was rate-limiting at low pH (pK* = 7.0 at -39 degrees C) and that collapse to the acylenzymes was rate-determining at high pH. When corrected for the effect of temperature and cosolvent, the rate of intermediate formation was in good agreement with that measured at 25 degrees C in aqueous solution by stopped-flow techniques. PMID:36609

  10. Compositional Controls on Melt Polymerization

    NASA Astrophysics Data System (ADS)

    Brugger, C.; Hammer, J.

    2005-12-01

    The structure and rheology of silicate melts are strongly controlled by composition, namely the concentrations of network-forming and -modifying cations. Melt viscosity is implicated in kinetic theories of phase transformations as a proxy for component mobility, which partly controls rates of crystal and bubble nucleation and growth. To anticipate reaction kinetics in magmas and focus experimental work on key variables, compositional controls on melt structure are systematically investigated using NBO/T (Mysen, 1988), the ratio of non-bridging oxygens to tetrahedrally coordinated cations. Silicon, ferric iron, and aluminum are network-formers, whereas alkalis and divalent cations are network-modifiers unless needed to charge-balance trivalent cations in tetrahedral coordination. NBO/T calculations are performed over 4D composition space (alkalis, silica, divalent and trivalent cations), in which 3 components are varied independently, creating a cube. We assess the effects of individual components using slices through the cube contoured for NBO/T. Ratios are also calculated for naturally occurring liquids and MELTS-generated liquid lines of descent derived from basalts with similar silica contents but varying in alkalis. Naturally occurring melts are highly polymerized (NBO/T of 0-1) compared to silicate minerals (0-4). Calculations show that replacing network-modifiers with network-formers decreases NBO/T; conversely, replacing formers with modifiers increases the ratio. However, polymerization increases when alumina replaces silica or when alkalis replace divalent cations. Natural alkali-rich melts tend to have fewer divalent cations than alkali-poor melts at similar silica contents, thus they are more polymerized and have higher viscosities. Contrary to common perception, the lower viscosities of highly differentiated alkalic melts (e.g. trachytes, phonolites) compared to silica-rich rhyolites are attributed to lower silica rather than greater alkalis. In fact

  11. Anion Gap Blood Test

    MedlinePlus

    ... Why do I need an anion gap blood test? Your health care provider may have ordered an anion gap blood ... which is a blood test. During a blood test, a health care professional uses a small needle to take a ...

  12. Kunststoffe (Polymere)

    NASA Astrophysics Data System (ADS)

    Weißbach, Wolfgang

    Polymere bestehen aus Riesen- oder Makromolekülen, die durch chemische Reaktionen aus einfachen, niedermolekularen Verbindungen entstehen, den Monomeren. Ausgangsstoffe sind überwiegend Kohlenwasserstoffe (KW), die größte Gruppe der C-Verbindungen. Sie müssen reaktionsfähige Stellen besitzen, das sind OH-Gruppen oder Dopppelbindungen.

  13. Porating anion-responsive copolymeric gels.

    PubMed

    England, Dustin; Yan, Feng; Texter, John

    2013-09-24

    A polymerizable ionic liquid surfactant, 1-(11-acryloyloxyundecyl)-3-methylimidiazolium bromide (ILBr), was copolymerized with methyl methacrylate (MMA) in aqueous microemulsions at 30% (ILBr w/w) and various water to MMA ratios. The ternary phase diagram of the ILBr/MMA/water system was constructed at 25 and 60 °C. Homopolymers and copolymers of ILBr and MMA were produced by thermally initiated chain radical microemulsion polymerization at various compositions in bicontinuous and reverse microemulsion subdomains. Microemulsion polymerization reaction products varied from being gel-like to solid, and these materials were analyzed by thermal and scanning electron microscopy methods. Microemulsion polymerized materials were insoluble in all solvents tested, consistent with light cross-linking. Ion exchange between Br(-) and PF6(-) in these copolymeric materials resulted in the formation of open-cell porous structures in some of these materials, as was confirmed by scanning electron microscopy (SEM). Several compositions illustrate the capture of prepolymerization nanoscale structure by thermally initiated polymerization, expanding the domain of compositions exhibiting this feat and yet to be demonstrated in any other system. Regular cylindrical pores in interpenetrating ILBr-co-MMA and PMMA networks are produced by anion exchange in the absence of templates. A percolating cluster/bicontinuous transition is "captured" by SEM after using anion exchange to visualize the mixed cluster/pore morphology. Some design principles for achieving this capture and for obtaining stimuli responsive solvogels are articulated, and the importance of producing solvogels in capturing the nanoscale is highlighted.

  14. Anion exchange membrane

    DOEpatents

    Verkade, John G; Wadhwa, Kuldeep; Kong, Xueqian; Schmidt-Rohr, Klaus

    2013-05-07

    An anion exchange membrane and fuel cell incorporating the anion exchange membrane are detailed in which proazaphosphatrane and azaphosphatrane cations are covalently bonded to a sulfonated fluoropolymer support along with anionic counterions. A positive charge is dispersed in the aforementioned cations which are buried in the support to reduce the cation-anion interactions and increase the mobility of hydroxide ions, for example, across the membrane. The anion exchange membrane has the ability to operate at high temperatures and in highly alkaline environments with high conductivity and low resistance.

  15. Anions in Cometary Comae

    NASA Technical Reports Server (NTRS)

    Charnley, Steven B.

    2011-01-01

    The presence of negative ions (anions) in cometary comae is known from Giotto mass spectrometry of IP/Halley. The anions 0-, OH-, C-, CH- and CN- have been detected, as well as unidentified anions with masses 22-65 and 85-110 amu (Chaizy et al. 1991). Organic molecular anions are known to have a significant impact on the charge balance of interstellar clouds and circumstellar envelopes and have been shown to act as catalysts for the gas-phase synthesis of larger hydrocarbon molecules in the ISM, but their importance in cometary comae has not yet been explored. We present details of the first attempt to model the chemistry of anions in cometary comae. Based on the combined chemical and hydro dynamical model of Rodgers & Charnley (2002), we investigate the role of large carbon-chain anions in cometary coma chemistry. We calculate the effects of these anions on coma thermodynamics, charge balance and examine their impact on molecule formation.

  16. Filled tetrahedral semiconductor Li3 Al N2 studied with optical absorption: Application of the interstitial insertion rule

    NASA Astrophysics Data System (ADS)

    Kushida, K.; Kaneko, Y.; Kuriyama, K.

    2004-12-01

    The band gap nature of a filled tetrahedral semiconductor Li3AlN2 [viewed as the assemblage of eight hypothetical zinc-blende AlN sublattices (Li0.5Al0.5N)- filled with He-like Li+ interstitials at the empty tetrahedral sites next to the anions] is studied by an optical absorption method. The optical absorption studies show a tendency that Li3AlN2 is direct with a band gap of 4.40eV , whereas zinc-blende AlN has been estimated to be indirect from a first-principles calculation. The band gap value was confirmed by photoacoustic spectroscopy. According to the interstitial insertion rule of Wood , these results suggest that the insertion of Li+ ions into the interstitial sites in hypothetical zinc-blende AlN sublattices (Li0.5Al0.5N)- causes an upward shift of the X conduction band due to a Pauli repulsion of conduction electrons, exposing the Γ point as the conduction band minimum and resulting in a direct band gap.

  17. Adsorption of carbon oxide on tetrahedral bimetallic gold-copper clusters

    NASA Astrophysics Data System (ADS)

    Gogol', V. V.; Pichugina, D. A.; Kuz'menko, N. E.

    2016-12-01

    The interaction between carbon oxide and [Au20-nCun]q clusters ( n = 0, 1, 19, 20 and q = 0, ±1) is studied by means of DFT/PBE in the scalar relativistic approximation. To establish the composition and structure of an adsorption site, isomers of bimetallic Au19Cu and AuCu19 particles with different positions of the heteroatom at an apex, edge, and face of the tetrahedral framework are considered. The optimized structures are used as the basis to determine the electronic properties of clusters (average bond energy per atom, difference of energies between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), ionization potential, electron affinity energy). The calculated parameters shrink as the copper content in clusters grows. Among the uncharged models, the highest CO adsorption energy is typical of Au19Cu, the heteroatom of which lies at a cluster's apex. The CO adsorption energy for cationic and anionic clusters grows in comparison to neutral clusters.

  18. Intense turquoise colors of apatite-type compounds with Mn5+ in tetrahedral coordination

    NASA Astrophysics Data System (ADS)

    Medina, Elena A.; Li, Jun; Stalick, Judith K.; Subramanian, M. A.

    2016-02-01

    The solid solutions of chlorapatite compounds Ba5Mn3-xVxO12Cl (x = 0-3.0) and Ba5Mn3-xPxO12Cl (x = 0-3.0) have been synthesized through solid state reactions and Pechini or sol-gel method using citric acid. The colors of the samples change from white (x = 3.0) through turquoise (x = 1.5) to dark green (x = 0) with increasing amount of manganese. Optical measurements reveal that the origin of the color is presumably a combination of d-d transitions of Mn5+ and cation-anion charge transfer from transition metals to oxygens. Near IR reflectance measurements indicate that synthesized compounds are promising materials for "cool pigments" applications. Magnetic measurements verify that manganese has two unpaired electrons and exhibits 5 + oxidation state. The IR spectra change systematically with sample compositions and the fingerprint region (700 cm-1 to 1100 cm-1) indicates characteristic bands belonging to (MnO4)3-, (VO4)3- and (PO4)3- functional groups. Structure refinements using neutron data confirm that Mn5+, V5+ and P5+ cations occupy the tetrahedral sites in the apatite structure.

  19. Constructing monocrystalline covalent organic networks by polymerization

    NASA Astrophysics Data System (ADS)

    Beaudoin, Daniel; Maris, Thierry; Wuest, James D.

    2013-10-01

    An emerging strategy for making ordered materials is modular construction, which connects preformed molecular subunits to neighbours through interactions of properly selected reactive sites. This strategy has yielded remarkable materials, including metal-organic frameworks joined by coordinative bonds, supramolecular networks linked by strong non-covalent interactions, and covalent organic frameworks in which atoms of carbon and other light elements are bonded covalently. However, the strategy has not yet produced covalently bonded organic materials in the form of large single crystals. Here we show that such materials can result from reversible self-addition polymerizations of suitably designed monomers. In particular, monomers with four tetrahedrally oriented nitroso groups polymerize to form diamondoid azodioxy networks that can be fully characterized by single-crystal X-ray diffraction. This work forges a strong new link between polymer science and supramolecular chemistry by showing how predictably ordered covalent or non-covalent structures can both be built using a single modular strategy.

  20. Chemistry of BDI*M2+ complexes (M = Mg, Zn) and their role in lactide polymerization where BDI* is the anion derived from methylenebis(C-(t)Bu, N-2,6-diisopropylphenyl)imine BDI*H.

    PubMed

    Ayala, Carla N; Chisholm, Malcolm H; Gallucci, Judith C; Krempner, Clemens

    2009-11-14

    The bulky diimine CH(2){C((t)Bu)N-2,6-Pr(i)(2)C(6)H(3)}(2), BDI*H, is shown to exist in two isomers trans-trans, 1a and cis-trans, 1b that interconvert slowly on the NMR time-scale. Treatment of the diimine with (n)BuLi in hexane proceeds slowly to give the lithium beta-diketoiminate LiBDI*, 2, which upon hydrolysis yields the eneimine tautomer of BDI*H which has been characterized by X-ray studies in three rotamers, 3a, 3b and 3c. Dialkylmetal compounds (M = Mg, R = Bu; M = Zn, R = Et) react with either 1 or 3 in hydrocarbon and ether solvents to give BDI*Mg((n)Bu)THF, 4, and BDI*ZnEt, 5, which have been structurally characterized. M(N(SiMe(3))(2))(2) compounds where M = Mg, Zn or Ca failed to react with either 1 or 3 in hydrocarbon solvents. The reactions between ZnCl(2) and 2 yield BDI*ZnCl, 6, and a further reaction with LiNMe(2) yields BDI*ZnNMe(2), 7. The compounds 5 and 6 are shown to contain trigonal planar, M(2+) ions. Compounds 4, and 7 initiate ring-opening polymerization, ROP, of rac-lactide to give atactic polylactide, PLA. The rate of ROP depends on the metal M = Mg > Zn and is slower than that observed for the related beta-diketoiminate complexes where the bulky-(t)Bu group is replaced by Me.

  1. On a combined adaptive tetrahedral tracing and edge diffraction model

    NASA Astrophysics Data System (ADS)

    Hart, Carl R.

    A major challenge in architectural acoustics is the unification of diffraction models and geometric acoustics. For example, geometric acoustics is insufficient to quantify the scattering characteristics of acoustic diffusors. Typically the time-independent boundary element method (BEM) is the method of choice. In contrast, time-domain computations are of interest for characterizing both the spatial and temporal scattering characteristics of acoustic diffusors. Hence, a method is sought that predicts acoustic scattering in the time-domain. A prediction method, which combines an advanced image source method and an edge diffraction model, is investigated for the prediction of time-domain scattering. Adaptive tetrahedral tracing is an advanced image source method that generates image sources through an adaptive process. Propagating tetrahedral beams adapt to ensonified geometry mapping the geometric sound field in space and along boundaries. The edge diffraction model interfaces with the adaptive tetrahedral tracing process by the transfer of edge geometry and visibility information. Scattering is quantified as the contribution of secondary sources along a single or multiple interacting edges. Accounting for a finite number of diffraction permutations approximates the scattered sound field. Superposition of the geometric and scattered sound fields results in a synthesized impulse response between a source and a receiver. Evaluation of the prediction technique involves numerical verification and numerical validation. Numerical verification is based upon a comparison with analytic and numerical (BEM) solutions for scattering geometries. Good agreement is shown for the selected scattering geometries. Numerical validation is based upon experimentally determined scattered impulse responses of acoustic diffusors. Experimental data suggests that the predictive model is appropriate for high-frequency predictions. For the experimental determination of the scattered impulse

  2. Platelet adhesion on phosphorus-incorporated tetrahedral amorphous carbon films

    NASA Astrophysics Data System (ADS)

    Liu, Aiping; Zhu, Jiaqi; Liu, Meng; Dai, Zhifei; Han, Xiao; Han, Jiecai

    2008-11-01

    The haemocompatibility of phosphorus-incorporated tetrahedral amorphous carbon (ta-C:P) films, synthesized by filtered cathodic vacuum arc technique with PH 3 as the dopant source, was assessed by in vitro platelet adhesion tests. Results based on scanning electron microscopy and contact angle measurements reveal that phosphorus incorporation improves the wettability and blood compatibility of ta-C film. Our studies may provide a novel approach for the design and synthesis of doped ta-C films to repel platelet adhesion and reduce thrombosis risk.

  3. Search for Fingerprints of Tetrahedral Symmetry in 156Gd

    NASA Astrophysics Data System (ADS)

    Doan, Q. T.; Curien, D.; Stęzowski, O.; Dudek, J.; Mazurek, K.; Góźdź, A.; Piot, J.; DuchÊNe, G.; Gall, B.; Molique, H.; Richet, M.; Medina, P.; Guinet, D.; Redon, N.; Schmitt, Ch.; Jones, P.; Peura, P.; Ketelhut, S.; Nyman, M.; Jakobsson, U.; Greenlees, P. T.; Julin, R.; Juutinen, S.; Rahkila, P.; Maj, A.; Zuber, K.; Bednarczyk, P.; Schunck, N.; Dobaczewski, J.; Astier, A.; Deloncle, I.; Verney, D.; de Angelis, G.; Gerl, J.

    2009-03-01

    Theoretical predictions suggest the presence of tetrahedral symmetry as an explanation for the vanishing intra-band E2 transitions at the bottom of the odd-spin negative-parity band in 156Gd. The present study reports on experiment performed to address this phenomenon. It allowed to remove certain ambiguouities related to the intra-band E2 transitions in the negative-parity bands, to determine the new inter-band transitions and reduced probability ratios B(E2)/B(E1) and, for the first time, to determine the experimental uncertainties related to the latter observable.

  4. Practical implementation of tetrahedral mesh reconstruction in emission tomography

    NASA Astrophysics Data System (ADS)

    Boutchko, R.; Sitek, A.; Gullberg, G. T.

    2013-05-01

    This paper presents a practical implementation of image reconstruction on tetrahedral meshes optimized for emission computed tomography with parallel beam geometry. Tetrahedral mesh built on a point cloud is a convenient image representation method, intrinsically three-dimensional and with a multi-level resolution property. Image intensities are defined at the mesh nodes and linearly interpolated inside each tetrahedron. For the given mesh geometry, the intensities can be computed directly from tomographic projections using iterative reconstruction algorithms with a system matrix calculated using an exact analytical formula. The mesh geometry is optimized for a specific patient using a two stage process. First, a noisy image is reconstructed on a finely-spaced uniform cloud. Then, the geometry of the representation is adaptively transformed through boundary-preserving node motion and elimination. Nodes are removed in constant intensity regions, merged along the boundaries, and moved in the direction of the mean local intensity gradient in order to provide higher node density in the boundary regions. Attenuation correction and detector geometric response are included in the system matrix. Once the mesh geometry is optimized, it is used to generate the final system matrix for ML-EM reconstruction of node intensities and for visualization of the reconstructed images. In dynamic PET or SPECT imaging, the system matrix generation procedure is performed using a quasi-static sinogram, generated by summing projection data from multiple time frames. This system matrix is then used to reconstruct the individual time frame projections. Performance of the new method is evaluated by reconstructing simulated projections of the NCAT phantom and the method is then applied to dynamic SPECT phantom and patient studies and to a dynamic microPET rat study. Tetrahedral mesh-based images are compared to the standard voxel-based reconstruction for both high and low signal-to-noise ratio

  5. Practical implementation of tetrahedral mesh reconstruction in emission tomography.

    PubMed

    Boutchko, R; Sitek, A; Gullberg, G T

    2013-05-07

    This paper presents a practical implementation of image reconstruction on tetrahedral meshes optimized for emission computed tomography with parallel beam geometry. Tetrahedral mesh built on a point cloud is a convenient image representation method, intrinsically three-dimensional and with a multi-level resolution property. Image intensities are defined at the mesh nodes and linearly interpolated inside each tetrahedron. For the given mesh geometry, the intensities can be computed directly from tomographic projections using iterative reconstruction algorithms with a system matrix calculated using an exact analytical formula. The mesh geometry is optimized for a specific patient using a two stage process. First, a noisy image is reconstructed on a finely-spaced uniform cloud. Then, the geometry of the representation is adaptively transformed through boundary-preserving node motion and elimination. Nodes are removed in constant intensity regions, merged along the boundaries, and moved in the direction of the mean local intensity gradient in order to provide higher node density in the boundary regions. Attenuation correction and detector geometric response are included in the system matrix. Once the mesh geometry is optimized, it is used to generate the final system matrix for ML-EM reconstruction of node intensities and for visualization of the reconstructed images. In dynamic PET or SPECT imaging, the system matrix generation procedure is performed using a quasi-static sinogram, generated by summing projection data from multiple time frames. This system matrix is then used to reconstruct the individual time frame projections. Performance of the new method is evaluated by reconstructing simulated projections of the NCAT phantom and the method is then applied to dynamic SPECT phantom and patient studies and to a dynamic microPET rat study. Tetrahedral mesh-based images are compared to the standard voxel-based reconstruction for both high and low signal-to-noise ratio

  6. Excluded volumes of clusters in tetrahedral particle packing

    NASA Astrophysics Data System (ADS)

    Liu, Lufeng; Lu, Peng; Meng, Lingyi; Jin, Weiwei; Li, Shuixiang

    2014-02-01

    We investigate the excluded volumes of clusters in tetrahedral particle packing using an ideal tetrahedron model and Monte Carlo simulation. Both the influences of the size and topology of clusters on the excluded volume are studied. We find that the excluded volumes of the dimer composed of two tetrahedra and the wagon wheel composed of five tetrahedra are relatively lower than other cluster forms. For large clusters, the excluded volume decreases when the topology of a cluster approaches the wagon-wheel geometry. The results give an explanation to the cluster distribution which demonstrates that the dimer and wagon wheel are the dominative cluster forms in the packing structure of tetrahedra.

  7. Structural performance of orthogonal tetrahedral truss Space-Station configurations

    NASA Technical Reports Server (NTRS)

    Dorsey, J. T.

    1984-01-01

    Two 150 kW space station configurations constructed with the orthogonal tetrahedral truss concept are described. One space station consists of a large central platform and two rotating solar wing arrays and the other consists of a long central keel with two rotating arrays. The dynamic characteristics of each configuration are obtained with and without nonstructural components present. The variation in frequencies and mass moments of inertia due to rotation of the two solar wing arrays are given for the long keel space station configuration. The structural performance of the solar wing array is assessed for cases where individual critical struts fail in the array support truss.

  8. Novel biomedical tetrahedral mesh methods: algorithms and applications

    NASA Astrophysics Data System (ADS)

    Yu, Xiao; Jin, Yanfeng; Chen, Weitao; Huang, Pengfei; Gu, Lixu

    2007-12-01

    Tetrahedral mesh generation algorithm, as a prerequisite of many soft tissue simulation methods, becomes very important in the virtual surgery programs because of the real-time requirement. Aiming to speed up the computation in the simulation, we propose a revised Delaunay algorithm which makes a good balance of quality of tetrahedra, boundary preservation and time complexity, with many improved methods. Another mesh algorithm named Space-Disassembling is also presented in this paper, and a comparison of Space-Disassembling, traditional Delaunay algorithm and the revised Delaunay algorithm is processed based on clinical soft-tissue simulation projects, including craniofacial plastic surgery and breast reconstruction plastic surgery.

  9. Search for Fingerprints of Tetrahedral Symmetry in ^{156}Gd

    SciTech Connect

    Doan, Q. T.; Curien, D.; Stezowski, O.; Dudek, J.; Mazurek, K.; Gozdz, A.; Piot, J.; Duchene, G.; Gall, B.; Molique, H.; Richet, M.; Guinet, D.; Redon, N.; Schmitt, Ch.; Jones, P.; Peura, P.; Ketelhut, S.; Nyman, M.; Jakobsson, U.; Greenlees, P. T.; Julin, R.; Juutinen, S.; Rahkila, P.; Maj, A.; Zuber, K.; Bednarczyk, P.; Schunck, N.; Dobaczewski, J.; Astier, A.; Deloncle, I.; Verney, D.; Gerl, J.

    2009-01-01

    Theoretical predictions suggest the presence of tetrahedral symmetry as an explanation for the vanishing intra-band E2 transitions at the bottom of the odd-spin negative-parity band in ^{156}Gd. The present study reports on experiment performed to address this phenomenon. It allowed to remove certain ambiguities related to the intra-band E2 transitions in the negative-parity bands to determine the new inter-band transitions and reduced probability ratios B(E2)/B(E1) and, for the first time, to determine the experimental uncertainties related to the latter observable.

  10. An aluminophosphate molecular sieve with 36 crystallographically distinct tetrahedral sites.

    PubMed

    Lee, Jun Kyu; Turrina, Alessandro; Zhu, Liangkui; Seo, Seungwan; Zhang, Daliang; Cox, Paul A; Wright, Paul A; Qiu, Shilun; Hong, Suk Bong

    2014-07-14

    The structure of the new medium-pore aluminophosphate molecular sieve PST-6 is determined by the combined use of rotation electron diffraction tomography, synchrotron X-ray powder diffraction, and computer modeling. PST-6 was prepared by calcination of another new aluminophosphate material with an unknown structure synthesized using diethylamine as a structure-directing agent, which is thought to contain bridging hydroxy groups. PST-6 has 36 crystallographically distinct tetrahedral sites in the asymmetric unit and is thus crystallographically the most complex zeolitic structure ever solved. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Probing the redox chemistry of titanium silicalite-1: formation of tetrahedral Ti3+ centers by reaction with triethylaluminum.

    PubMed

    Morra, Elena; Giamello, Elio; Chiesa, Mario

    2014-06-10

    Transition-metal ions with open-shell configurations hold promise in the development of novel coordination chemistry and potentially unprecedented redox catalysis. Framework-substituted Ti(3+) ions with tetrahedral coordination are generated by reductive activation of titanium silicalite-1 with triethylaluminum, an indispensable co-catalyst for heterogeneous Ziegler-Natta polymerization catalysts. Continuous-wave and pulse electron paramagnetic resonance methods are applied to unravel details on the local environment of the reduced transition metal-ions, which are shown to be part of the silica framework by detection of (29)Si hyperfine interactions. The chemical accessibility of the reduced sites is probed using ammonia as probe molecule. Evidence is found for the coordination of a single ammonia molecule. Comparison to similar systems, such as TiAlPO-5, reveals clear differences in the coordination chemistry of the reduced Ti sites in the two solids, which may be understood considering the different electronic properties of the solid frameworks.

  12. Methods for prismatic/tetrahedral grid generation and adaptation

    NASA Astrophysics Data System (ADS)

    Kallinderis, Y.

    1995-10-01

    The present work involves generation of hybrid prismatic/tetrahedral grids for complex 3-D geometries including multi-body domains. The prisms cover the region close to each body's surface, while tetrahedra are created elsewhere. Two developments are presented for hybrid grid generation around complex 3-D geometries. The first is a new octree/advancing front type of method for generation of the tetrahedra of the hybrid mesh. The main feature of the present advancing front tetrahedra generator that is different from previous such methods is that it does not require the creation of a background mesh by the user for the determination of the grid-spacing and stretching parameters. These are determined via an automatically generated octree. The second development is a method for treating the narrow gaps in between different bodies in a multiply-connected domain. This method is applied to a two-element wing case. A High Speed Civil Transport (HSCT) type of aircraft geometry is considered. The generated hybrid grid required only 170 K tetrahedra instead of an estimated two million had a tetrahedral mesh been used in the prisms region as well. A solution adaptive scheme for viscous computations on hybrid grids is also presented. A hybrid grid adaptation scheme that employs both h-refinement and redistribution strategies is developed to provide optimum meshes for viscous flow computations. Grid refinement is a dual adaptation scheme that couples 3-D, isotropic division of tetrahedra and 2-D, directional division of prisms.

  13. Numerical Simulation of the Radiation Symmetry in Tetrahedral Hohlraums.

    NASA Astrophysics Data System (ADS)

    Macfarlane, J. J.; Magelssen, G.; Delamater, N.; Wallace, J.; Murphy, T.; Klare, K.

    1997-11-01

    The successful implosion of a capsule in indirect-drive ICF experiments requires the ability to diagnose and control the radiation symmetry at its surface. Recently, there has been increased interest in studying whether ``tetrahedral'' hohlraums can produce a radiation field on the capsule which is more symmetric than cylindrical hohlraums. Asymmetries in the 3-D radiation field are influenced by: the size and shape of the hohlraum, the wall albedo, the capsule radius, the LEH and diagnostic holes, and the laser beam pointing and power/energy imbalances. Time-dependent asymmetries are caused by the laser pulse history, changing wall albedos, and wall motion. We have recently developed a 3-D view factor code to investigate the time-dependent radiation asymmetry in indirect-drive ICF experiments. This code includes algorithms for the accurate solution of configuration factors, as well as laser ray-trace algorithms for modeling OMEGA, NOVA, and NIF laser/target chamber geometries. Time-dependent albedos are based on 1-D radiation-hydrodynamics simulations using UTA opacities for the high-Z wall. We will present results from simulations of OMEGA tetrahedral hohlraum experiments, as well as simulations showing how asymmetries scale with capsule/hohlraum configuration.

  14. Methods for prismatic/tetrahedral grid generation and adaptation

    NASA Technical Reports Server (NTRS)

    Kallinderis, Y.

    1995-01-01

    The present work involves generation of hybrid prismatic/tetrahedral grids for complex 3-D geometries including multi-body domains. The prisms cover the region close to each body's surface, while tetrahedra are created elsewhere. Two developments are presented for hybrid grid generation around complex 3-D geometries. The first is a new octree/advancing front type of method for generation of the tetrahedra of the hybrid mesh. The main feature of the present advancing front tetrahedra generator that is different from previous such methods is that it does not require the creation of a background mesh by the user for the determination of the grid-spacing and stretching parameters. These are determined via an automatically generated octree. The second development is a method for treating the narrow gaps in between different bodies in a multiply-connected domain. This method is applied to a two-element wing case. A High Speed Civil Transport (HSCT) type of aircraft geometry is considered. The generated hybrid grid required only 170 K tetrahedra instead of an estimated two million had a tetrahedral mesh been used in the prisms region as well. A solution adaptive scheme for viscous computations on hybrid grids is also presented. A hybrid grid adaptation scheme that employs both h-refinement and redistribution strategies is developed to provide optimum meshes for viscous flow computations. Grid refinement is a dual adaptation scheme that couples 3-D, isotropic division of tetrahedra and 2-D, directional division of prisms.

  15. Surface-induced crystallization in supercooled tetrahedral liquids.

    PubMed

    Li, Tianshu; Donadio, Davide; Ghiringhelli, Luca M; Galli, Giulia

    2009-09-01

    Surfaces have long been known to have an intricate role in solid-liquid phase transformations. Whereas melting is often observed to originate at surfaces, freezing usually starts in the bulk, and only a few systems have been reported to exhibit signatures of surface-induced crystallization. These include assembly of chain-like molecules, some liquid metals and alloys and silicate glasses. Here, we report direct computational evidence of surface-induced nucleation in supercooled liquid silicon and germanium, and we illustrate the crucial role of free surfaces in the freezing process of tetrahedral liquids exhibiting a negative slope of their melting lines (dT/dP|coexist<0). Our molecular dynamics simulations show that the presence of free surfaces may enhance the nucleation rates by several orders of magnitude with respect to those found in the bulk. Our findings provide insight, at the atomistic level, into the nucleation mechanism of widely used semiconductors, and support the hypothesis of surface-induced crystallization in other tetrahedrally coordinated systems, in particular water in the atmosphere.

  16. Acoustic Detection and Tracking of a Class I UAS with a Small Tetrahedral Microphone Array

    DTIC Science & Technology

    2014-09-01

    Acoustic Detection and Tracking of a Class I UAS with a Small Tetrahedral Microphone Array by Minas Benyamin and Geoffrey H Goldman ARL...20783-1138 ARL-TR-7086 September 2014 Acoustic Detection and Tracking of a Class I UAS with a Small Tetrahedral Microphone Array Minas...with a Small Tetrahedral Microphone Array 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) Minas Benyamin and

  17. Anion exchange polymer electrolytes

    DOEpatents

    Kim, Yu Seung; Kim, Dae Sik; Lee, Kwan-Soo

    2013-07-23

    Solid anion exchange polymer electrolytes and compositions comprising chemical compounds comprising a polymeric core, a spacer A, and a guanidine base, wherein said chemical compound is uniformly dispersed in a suitable solvent and has the structure: ##STR00001## wherein: i) A is a spacer having the structure O, S, SO.sub.2, --NH--, --N(CH.sub.2).sub.n, wherein n=1-10, --(CH.sub.2).sub.n--CH.sub.3--, wherein n=1-10, SO.sub.2-Ph, CO-Ph, ##STR00002## wherein R.sub.5, R.sub.6, R.sub.7 and R.sub.8 each are independently --H, --NH.sub.2, F, Cl, Br, CN, or a C.sub.1-C.sub.6 alkyl group, or any combination of thereof; ii) R.sub.9, R.sub.10, R.sub.11, R.sub.12, or R.sub.13 each independently are --H, --CH.sub.3, --NH.sub.2, --NO, --CH.sub.nCH.sub.3 where n=1-6, HC.dbd.O--, NH.sub.2C.dbd.O--, --CH.sub.nCOOH where n=1-6, --(CH.sub.2).sub.n--C(NH.sub.2)--COOH where n=1-6, --CH--(COOH)--CH.sub.2--COOH, --CH.sub.2--CH(O--CH.sub.2CH.sub.3).sub.2, --(C.dbd.S)--NH.sub.2, --(C.dbd.NH)--N--(CH.sub.2).sub.nCH.sub.3, where n=0-6, --NH--(C.dbd.S)--SH, --CH.sub.2--(C.dbd.O)--O--C(CH.sub.3).sub.3, --O--(CH.sub.2).sub.n--CH--(NH.sub.2)--COOH, where n=1-6, --(CH.sub.2).sub.n--CH.dbd.CH wherein n=1-6, --(CH.sub.2).sub.n--CH--CN wherein n=1-6, an aromatic group such as a phenyl, benzyl, phenoxy, methylbenzyl, nitrogen-substituted benzyl or phenyl groups, a halide, or halide-substituted methyl groups; and iii) wherein the composition is suitable for use in a membrane electrode assembly.

  18. Biokompatible Polymere

    NASA Astrophysics Data System (ADS)

    Ha, Suk-Woo; Wintermantel, Erich; Maier, Gerhard

    Der klinische Einsatz von synthetischen Polymeren begann in den 60-er Jahren in Form von Einwegartikeln, wie beispielsweise Spritzen und Kathetern, vor allem aufgrund der Tatsache, dass Infektionen infolge nicht ausreichender Sterilität der wiederverwendbaren Artikel aus Glas und metallischen Werkstoffen durch den Einsatz von sterilen Einwegartikeln signifikant reduziert werden konnten [1]. Die Einführung der medizinischen Einwegartikel aus Polymeren erfolgte somit nicht nur aus ökonomischen, sondern auch aus hygienischen Gründen. Wegen der steigenden Anzahl synthetischer Polymere und dem zunehmenden Bedarf an ärztlicher Versorgung reicht die Anwendung von Polymeren in der Medizin von preisgünstigen Einwegartikeln, die nur kurzzeitig intrakorporal eingesetzt werden, bis hin zu Implantaten, welche über eine längere Zeit grossen Beanspruchungen im menschlichen Körper ausgesetzt sind. Die steigende Verbreitung von klinisch eingesetzten Polymeren ist auf ihre einfache und preisgünstige Verarbeitbarkeit in eine Vielzahl von Formen und Geometrien sowie auf ihr breites Eigenschaftsspektrum zurückzuführen. Polymere werden daher in fast allen medizinischen Bereichen eingesetzt.

  19. Pseudo-fivefold diffraction symmetries in tetrahedral packing.

    PubMed

    Lee, Stephen; Henderson, Ryan; Kaminsky, Corey; Nelson, Zachary; Nguyen, Jeffers; Settje, Nick F; Schmidt, Joshua Teal; Feng, Ji

    2013-07-29

    We review the way in which atomic tetrahedra composed of metallic elements pack naturally into fused icosahedra. Orthorhombic, hexagonal, and cubic intermetallic crystals based on this packing are all shown to be united in having pseudo-fivefold rotational diffraction symmetry. A unified geometric model involving the 600-cell is presented: the model accounts for the observed pseudo-fivefold symmetries among the different Bravais lattice types. The model accounts for vertex-, edge-, polygon-, and cell-centered fused-icosahedral clusters. Vertex-centered and edge-centered types correspond to the well-known pseudo-fivefold symmetries in Ih and D5h quasicrystalline approximants. The concept of a tetrahedrally-packed reciprocal space cluster is introduced, the vectors between sites in this cluster corresponding to the principal diffraction peaks of fused-icosahedrally-packed crystals. This reciprocal-space cluster is a direct result of the pseudosymmetry and, just as the real-space clusters, can be rationalized by the 600-cell. The reciprocal space cluster provides insights for the Jones model of metal stability. For tetrahedrally-packed crystals, Jones zone faces prove to be pseudosymmetric with one another. Lower and upper electron per atom bounds calculated for this pseudosymmetry-based Jones model are shown to accord with the observed electron counts for a variety of Group 10-12 tetrahedrally-packed structures, among which are the four known Cu/Cd intermetallic compounds: CdCu2, Cd3Cu4, Cu5Cd8, and Cu3Cd10. The rationale behind the Jones lower and upper bounds is reviewed. The crystal structure of Zn11Au15Cd23, an example of a 1:1 MacKay cubic quasicrystalline approximant based solely on Groups 10-12 elements is presented. This compound crystallizes in Im3 (space group no. 204) with a = 13.842(2) Å. The structure was solved with R1 = 3.53 %, I > 2σ; = 5.33 %, all data with 1282/0/38 data/restraints/parameters. Copyright © 2013 WILEY-VCH Verlag GmbH & Co

  20. Anion solvation in alcohols

    SciTech Connect

    Jonah, C.D.; Xujia, Zhang; Lin, Yi

    1996-03-01

    Anion solvation is measured in alcohols using pump-probe pulse radiolysis and the activation energy of solvation is determined. Solvation of an anion appears to be different than excited state solvation. The continuum dielectric model does not appear to explain the results.

  1. Tetrahedral bonding in twisted bilayer graphene by carbon intercalation

    NASA Astrophysics Data System (ADS)

    Roy, Anindya; Pal, Hridis K.

    2017-08-01

    Based on ab initio calculations, we study the effect of intercalating twisted bilayer graphene with carbon. Surprisingly, we find that the intercalant pulls the atoms in the two layers closer together locally when placed in certain regions in between the layers, and the process is energetically favorable as well. This arises because in these regions of the supercell, the local environment allows the intercalant to form tetrahedral bonding with nearest atoms in the layers. Intercalating AB- or AA-bilayer graphene with carbon does not produce this effect; therefore, the nontrivial effect owes its origin to both using carbon as an intercalant and using twisted bilayer graphene as the host. This opens new routes to manipulating bilayer and multilayer van der Waals heterostructures and tuning their properties in an unconventional way.

  2. How does tetrahedral structure grow in liquid silicon upon supercooling?

    PubMed

    Morishita, Tetsuya

    2006-10-20

    We present an extensive set of isothermal-isobaric first-principles molecular-dynamics simulations of liquid silicon over a temperature range of 950-1700 K. We find that the tetrahedral order gradually grows upon cooling to approximately 1200 K, but that the growth accelerates significantly below approximately 1200 K. This growth process gives rise to anomalous changes in density and liquid structure upon supercooling. In particular, we find that the atomic coordination number remains constant to approximately 1200 K and then begins to decrease below approximately 1200 K, which resolves the existing controversy regarding liquid structure in the supercooled regime [T. H. Kim, Phys. Rev. Lett. 95, 085501 (2005)10.1103/PhysRevLett.95.085501].

  3. Nuclear tetrahedral symmetry: possibly present throughout the periodic table.

    PubMed

    Dudek, J; Goźdź, A; Schunck, N; Miśkiewicz, M

    2002-06-24

    More than half a century after the fundamental, spherical shell structure in nuclei had been established, theoretical predictions indicated that the shell gaps comparable or even stronger than those at spherical shapes may exist. Group-theoretical analysis supported by realistic mean-field calculations indicate that the corresponding nuclei are characterized by the TD(d) ("double-tetrahedral") symmetry group. Strong shell-gap structure is enhanced by the existence of the four-dimensional irreducible representations of TD(d); it can be seen as a geometrical effect that does not depend on a particular realization of the mean field. Possibilities of discovering the TD(d) symmetry in experiment are discussed.

  4. Photoconductive detection of tetrahedrally coordinated hydrogen in ZnO.

    PubMed

    Koch, S G; Lavrov, E V; Weber, J

    2012-04-20

    In this Letter we apply an innovative experimental approach, which allows us to improve the sensitivity of detecting local vibrational modes (LVMs) even in highly absorbing spectral regions. This photoconductive technique allowed us to confirm a recent suggestion of a new multicenter bond for hydrogen in ZnO [A. Janotti and C. G. Van de Walle, Nature Mater. 6, 44 (2007)]. The two LVMs of the hydrogen substituting oxygen in ZnO are identified at 742 and 792 cm(-1). The modes belong to a nondegenerated A(1) and a twofold degenerated E representations of the C(3v) point group. The tetrahedral coordination of the hydrogen atom is the result of a newly detected multicenter bond for defects in solids.

  5. A radiative model of quark masses with binary tetrahedral symmetry

    NASA Astrophysics Data System (ADS)

    Natale, Alexander

    2017-01-01

    A radiative model of quark and lepton masses utilizing the binary tetrahedral (T‧) flavor symmetry, or horizontal symmetry, is proposed which produces the first two generation of quark masses through their interactions with vector-like quarks that carry charges under an additional U (1). By softly-breaking the T‧ to a residual Z4 through the vector-like quark masses, a CKM mixing angle close to the Cabibbo angle is produced. In order to generate the cobimaximal neutrino oscillation pattern (θ13 ≠ 0 ,θ23 = π / 4 ,δCP = ± π / 2) and protect the horizontal symmetry from arbitrary corrections in the lepton sector, there are automatically two stabilizing symmetries in the dark sector. Several benchmark cases where the correct relic density is achieved in a multi-component DM scenario, as well as the potential collider signatures of the vector-like quarks are discussed.

  6. Slave fermion formalism for the tetrahedral spin chain

    NASA Astrophysics Data System (ADS)

    Mohan, Priyanka; Rao, Sumathi

    2016-09-01

    We use the SU(2) slave fermion approach to study a tetrahedral spin 1/2 chain, which is a one-dimensional generalization of the two dimensional Kitaev honeycomb model. Using the mean field theory, coupled with a gauge fixing procedure to implement the single occupancy constraint, we obtain the phase diagram of the model. We then show that it matches the exact results obtained earlier using the Majorana fermion representation. We also compute the spin-spin correlation in the gapless phase and show that it is a spin liquid. Finally, we map the one-dimensional model in terms of the slave fermions to the model of 1D p-wave superconducting model with complex parameters and show that the parameters of our model fall in the topological trivial regime and hence does not have edge Majorana modes.

  7. Photonuclear sum rules and the tetrahedral configuration of He4

    NASA Astrophysics Data System (ADS)

    Gazit, Doron; Barnea, Nir; Bacca, Sonia; Leidemann, Winfried; Orlandini, Giuseppina

    2006-12-01

    Three well-known photonuclear sum rules (SR), i.e., the Thomas-Reiche-Kuhn, the bremsstrahlungs and the polarizability SR are calculated for He4 with the realistic nucleon-nucleon potential Argonne V18 and the three-nucleon force Urbana IX. The relation between these sum rules and the corresponding energy weighted integrals of the cross section is discussed. Two additional equivalences for the bremsstrahlungs SR are given, which connect it to the proton-neutron and neutron-neutron distances. Using them, together with our result for the bremsstrahlungs SR, we find a deviation from the tetrahedral symmetry of the spatial configuration of He4. The possibility to access this deviation experimentally is discussed.

  8. Structural and electronic properties of a tetrahedral amorphous carbon surface

    NASA Astrophysics Data System (ADS)

    Dong, Jianjun; Drabold, D. A.

    1997-03-01

    We present ab initio studies of a model of tetrahedral amorphous carbon (ta-C) surface. Our methodology is LDA (with Harris functional and local basis) molecular dynamics simulations. The surface is modeled by a 216 atom slab supercell. Several candidate slabs are constructed by starting with the DTW model (B.R. Djordjevic, M.F. Thorpe and F. Wooten, Phys. Rev. B 52) 5685 (1995) and applying various simulated heating/quenching cycles. We analyze the structural and electronic properties of the surface , with special attention forcused on the electronic signatures of surface structural defects. Preliminary results indicate that the surface layer significantly graphitizes, and many surface gap states are present in the electronic density of states.

  9. Optimization of Time-Dependent Particle Tracing Using Tetrahedral Decomposition

    NASA Technical Reports Server (NTRS)

    Kenwright, David; Lane, David

    1995-01-01

    An efficient algorithm is presented for computing particle paths, streak lines and time lines in time-dependent flows with moving curvilinear grids. The integration, velocity interpolation and step-size control are all performed in physical space which avoids the need to transform the velocity field into computational space. This leads to higher accuracy because there are no Jacobian matrix approximations or expensive matrix inversions. Integration accuracy is maintained using an adaptive step-size control scheme which is regulated by the path line curvature. The problem of cell-searching, point location and interpolation in physical space is simplified by decomposing hexahedral cells into tetrahedral cells. This enables the point location to be done analytically and substantially faster than with a Newton-Raphson iterative method. Results presented show this algorithm is up to six times faster than particle tracers which operate on hexahedral cells yet produces almost identical particle trajectories.

  10. Self-assembly of tetrahedral plasmonic nanoclusters for optical metafluids

    NASA Astrophysics Data System (ADS)

    Schade, Nicholas; Manoharan, Vinothan

    2015-03-01

    We direct the assembly of clusters of gold nanospheres that behave as nanoscale electromagnetic resonators. We use spherical gold nanoparticles that are exceptionally smooth, monocrystalline, and monodisperse. These particles exhibit highly reproducible scattering spectra compared with gold colloids that are available commercially. We mix these positively charged particles with negatively charged dielectric particles. The gold particles stick to the dielectric particles permanently and randomly in a process that can be modeled mathematically as ``random parking,'' a type of non-equilibrium self-assembly. By controlling the particles' sizes, stoichiometry, and interactions, we maximize the yield of tetrahedral clusters, the ideal structures for isotropic metamaterials. We measure the optical properties of these structures with dark-field spectroscopy to characterize their suitability as building blocks for a bulk, isotropic, optical metafluid.

  11. A bicontinuous tetrahedral structure in a liquid-crystalline lipid

    NASA Astrophysics Data System (ADS)

    Longley, William; McIntosh, Thomas J.

    1983-06-01

    The structure of most lipid-water phases can be visualized as an ordered distribution of two liquid media, water and hydrocarbons, separated by a continuous surface covered by the polar groups of the lipid molecules1. In the cubic phases in particular, rod-like elements are linked into three-dimensional networks1,2. Two of these phases (space groups Ia3d and Pn3m) contain two such three-dimensional networks mutually inter-woven and unconnected. Under the constraints of energy minimization3, the interface between the components in certain of these `porous fluids' may well resemble one of the periodic minimal surface structures of the type described mathematically by Schwarz4,5. A structure of this sort has been proposed for the viscous isotropic (cubic) form of glycerol monooleate (GMO) by Larsson et al.6 who suggested that the X-ray diagrams of Lindblom et al.7 indicated a body-centred crystal structure in which lipid bilayers might be arranged as in Schwarz's octahedral surface4. We have now found that at high water contents, a primitive cubic lattice better fits the X-ray evidence with the material in the crystal arranged in a tetrahedral way. The lipid appears to form a single bilayer, continuous in three dimensions, separating two continuous interlinked networks of water. Each of the water networks has the symmetry of the diamond crystal structure and the bilayer lies in the space between them following a surface resembling Schwarz's tetrahedral surface4.

  12. Exploring the aryl esterase catalysis of paraoxonase-1 through solvent kinetic isotope effects and phosphonate-based isosteric analogues of the tetrahedral reaction intermediate.

    PubMed

    Bavec, Aljoša; Knez, Damijan; Makovec, Tomaž; Stojan, Jure; Gobec, Stanislav; Goličnik, Marko

    2014-11-01

    Although a recent study of Debord et al. in Biochimie (2014; 97:72-77) described the thermodynamics of the catalysed hydrolysis of phenyl acetate by human paraoxonase-1, the mechanistic details along the reaction route of this enzyme remain unclear. Therefore, we briefly present the solvent kinetic isotope effects on the phenyl acetate esterase activity of paraoxonase-1 and its inhibition with the phenyl methylphosphonate anion, which is a stable isosteric analogue that mimics the high-energy tetrahedral intermediate on the hydroxide-promoted hydrolysis pathway. The data show normal isotope effects, while proton inventory analysis indicates that two protons contribute to the kinetic isotope effect. Coherently, moderate competitive inhibition with the phenyl methylphosphonate anion reveals that the rate-limiting transition state suboptimally resembles the tetrahedral intermediate. The implications of these findings can be attributed to two possible reaction mechanisms that might occur during the paraoxonase-1-catalysed hydrolysis of phenyl acetate. Copyright © 2014 Elsevier B.V. and Société française de biochimie et biologie Moléculaire (SFBBM). All rights reserved.

  13. Photoelectron Spectroscopy and Theoretical Studies of Anion-pi Interactions: Binding Strength and Anion Specificity

    SciTech Connect

    Zhang, Jian; Zhou, Bin; Sun, Zhenrong; Wang, Xue B.

    2015-01-01

    Proposed in theory and confirmed to exist, anion–π interactions have been recognized as new and important non-covalent binding forces. Despite extensive theoretical studies, numerous crystal structural identifications, and a plethora of solution phase investigations, intrinsic anion–π interaction strengths that are free from complications of condensed phases’ environments, have not been directly measured in the gas phase. Herein we present a joint photoelectron spectroscopic and theoretical study on this subject, in which tetraoxacalix[2]arene[2]triazine 1, an electron-deficient and cavity self-tunable macrocyclic was used as a charge-neutral molecular host to probe its interactions with a series of anions with distinctly different shapes and charge states (spherical halides Cl⁻, Br⁻, I⁻, linear thiocyanate SCN⁻, trigonal planar nitrate NO₃⁻, pyramidic iodate IO₃⁻, and tetrahedral sulfate SO₄²⁻). The binding energies of the resultant gaseous 1:1 complexes (1•Cl⁻,1•Br⁻, 1•I⁻, 1•SCN⁻, 1•NO₃⁻, 1•IO₃⁻ and 1•SO₄²⁻) were directly measured experimentally, exhibiting substantial non-covalent interactions with pronounced anion specific effects. The binding strengths of Cl⁻, NO₃⁻, IO₃⁻ with 1 are found to be strongest among all singly charged anions, amounting to ca. 30 kcal/mol, but only about 40% of that between 1 and SO₄²⁻. Quantum chemical calculations reveal that all anions reside in the center of the cavity of 1 with anion–π binding motif in the complexes’ optimized structures, where 1 is seen to be able to self-regulate its cavity structure to accommodate anions of different geometries and three-dimensional shapes. Electron density surface and natural bond orbital charge distribution analysis further support anion–π binding formation. The calculated binding energies of the anions and 1 nicely reproduce the experimentally estimated electron binding energy increase. This work

  14. An 8-node tetrahedral finite element suitable for explicit transient dynamic simulations

    SciTech Connect

    Key, S.W.; Heinstein, M.W.; Stone, C.M.

    1997-12-31

    Considerable effort has been expended in perfecting the algorithmic properties of 8-node hexahedral finite elements. Today the element is well understood and performs exceptionally well when used in modeling three-dimensional explicit transient dynamic events. However, the automatic generation of all-hexahedral meshes remains an elusive achievement. The alternative of automatic generation for all-tetrahedral finite element is a notoriously poor performer, and the 10-node quadratic tetrahedral finite element while a better performer numerically is computationally expensive. To use the all-tetrahedral mesh generation extant today, the authors have explored the creation of a quality 8-node tetrahedral finite element (a four-node tetrahedral finite element enriched with four midface nodal points). The derivation of the element`s gradient operator, studies in obtaining a suitable mass lumping and the element`s performance in applications are presented. In particular, they examine the 80node tetrahedral finite element`s behavior in longitudinal plane wave propagation, in transverse cylindrical wave propagation, and in simulating Taylor bar impacts. The element only samples constant strain states and, therefore, has 12 hourglass modes. In this regard, it bears similarities to the 8-node, mean-quadrature hexahedral finite element. Given automatic all-tetrahedral meshing, the 8-node, constant-strain tetrahedral finite element is a suitable replacement for the 8-node hexahedral finite element and handbuilt meshes.

  15. Why Is the Tetrahedral Bond Angle 109 Degrees? The Tetrahedron-in-a-Cube

    ERIC Educational Resources Information Center

    Lim, Kieran F.

    2012-01-01

    The common question of why the tetrahedral angle is 109.471 degrees can be answered using a tetrahedron-in-a-cube, along with some Year 10 level mathematics. The tetrahedron-in-a-cube can also be used to demonstrate the non-polarity of tetrahedral molecules, the relationship between different types of lattice structures, and to demonstrate that…

  16. Collision-broadened linewidths of tetrahedral molecules. III - Dispersion and induction interactions

    NASA Technical Reports Server (NTRS)

    Varanasi, P.

    1975-01-01

    Expressions for the interruption functions S2(b) have been derived for the dispersion interaction between a tetrahedral molecule and a linear molecule, and for the interaction between the octopole moment of a tetrahedral molecule and the octopole-induced dipole moment in a perturbing molecule.

  17. Why Is the Tetrahedral Bond Angle 109 Degrees? The Tetrahedron-in-a-Cube

    ERIC Educational Resources Information Center

    Lim, Kieran F.

    2012-01-01

    The common question of why the tetrahedral angle is 109.471 degrees can be answered using a tetrahedron-in-a-cube, along with some Year 10 level mathematics. The tetrahedron-in-a-cube can also be used to demonstrate the non-polarity of tetrahedral molecules, the relationship between different types of lattice structures, and to demonstrate that…

  18. Anions coordinating anions: analysis of the interaction between anionic Keplerate nanocapsules and their anionic ligands.

    PubMed

    Melgar, Dolores; Bandeira, Nuno A G; Bonet Avalos, Josep; Bo, Carles

    2017-02-15

    Keplerates are a family of anionic metal oxide spherical capsules containing up to 132 metal atoms and some hundreds of oxygen atoms. These capsules holding a high negative charge of -12 coordinate both mono-anionic and di-anionic ligands thus increasing their charge up to -42, even up to -72, which is compensated by the corresponding counter-cations in the X-ray structures. We present an analysis of the relative importance of several energy terms of the coordinate bond between the capsule and ligands like carbonate, sulphate, sulphite, phosphinate, selenate, and a variety of carboxylates, of which the overriding component is contributed by solvation/de-solvation effects.

  19. Bimetallic complexes and polymerization catalysts therefrom

    DOEpatents

    Patton, Jasson T.; Marks, Tobin J.; Li, Liting

    2000-11-28

    Group 3-6 or Lanthanide metal complexes possessing two metal centers, catalysts derived therefrom by combining the same with strong Lewis acids, Bronsted acid salts, salts containing a cationic oxidizing agent or subjected to bulk electrolysis in the presence of compatible, inert non-coordinating anions and the use of such catalysts for polymerizing olefins, diolefins and/or acetylenically unsaturated monomers are disclosed.

  20. A Family of Uniform Strain Tetrahedral Elements and a Method for Connecting Dissimilar Finite Element Meshes

    SciTech Connect

    Dohrmann, C.R.; Heinstein, M.W.; Jung, J.; Key, S.W.

    1999-01-01

    This report documents a collection of papers on a family of uniform strain tetrahedral finite elements and their connection to different element types. Also included in the report are two papers which address the general problem of connecting dissimilar meshes in two and three dimensions. Much of the work presented here was motivated by the development of the tetrahedral element described in the report "A Suitable Low-Order, Eight-Node Tetrahedral Finite Element For Solids," by S. W. Key {ital et al.}, SAND98-0756, March 1998. Two basic issues addressed by the papers are: (1) the performance of alternative tetrahedral elements with uniform strain and enhanced uniform strain formulations, and (2) the proper connection of tetrahedral and other element types when two meshes are "tied" together to represent a single continuous domain.

  1. Polymerization by classical and frustrated Lewis pairs.

    PubMed

    Chen, Eugene Y-X

    2013-01-01

    Main-group classical and frustrated Lewis pairs (CLPs and FLPs) comprising strong Lewis acids (LAs) and strong Lewis bases (LBs) are highly active for polymerization of conjugated polar alkenes, affording typically high molecular weight polymers with relatively narrow molecular weight distributions. Especially effective systems are the Lewis pairs (LPs) consisting of the strong LA Al(C6F5)3 and strong LBs, such as achiral phosphines and chiral chelating diphosphines, N-heterocyclic carbenes, and phosphazene superbases, for polymerization of methacrylates and acrylamides as well as renewable α-methylene-γ-butyrolactones. Chain initiation involves cooperative addition of LPs to the monomer to generate zwitterionic active species, and chain propagation proceeds via a bimetallic, activated-monomer addition mechanism. Transition metal nucleophile/electrophile pairs comprising neutral metallocene bis(ester enolate)s and strong LAs E(C6F5)3 (E = Al, B) generate two drastically different polymerization systems, depending on the LA. With E = Al, catalyst activation and chain initiating events lead to dually active ion-pairs, thereby effecting ion-pairing polymerization that affords polymers with unique stereo-multiblock microstructures. With E = B, on the other hand, the FLP-induced catalyst activation generates metallacyclic cations paired with the hydridoborate anion [HB(C6F5)3](-); uniquely, such ion-pairs effect catalytic polymerization of conjugated polar alkenes by an H-shuttling mechanism, with the cation catalyzing chain growth and the anion promoting chain transfer by shuttling the hydride between the cation and anion centers through the neutral borane.

  2. R type anion channel

    PubMed Central

    Diatloff, Eugene; Peyronnet, Rémi; Colcombet, Jean; Thomine, Sébastien; Barbier-Brygoo, Hélène

    2010-01-01

    Plant genomes code for channels involved in the transport of cations, anions and uncharged molecules through membranes. Although the molecular identity of channels for cations and uncharged molecules has progressed rapidly in the recent years, the molecular identity of anion channels has lagged behind. Electrophysiological studies have identified S-type (slow) and R-type (rapid) anion channels. In this brief review, we summarize the proposed functions of the R-type anion channels which, like the S-type, were first characterized by electrophysiology over 20 years ago, but unlike the S-type, have still yet to be cloned. We show that the R-type channel can play multiple roles. PMID:21051946

  3. Studies of Oxide Anions

    DTIC Science & Technology

    1991-06-01

    oxide and metal hydroxide anions and related clusters of species including ones comprised of tungsten, tantalum , molybdenum and niobium . After...molybdenum, tantalum and niobium were produced. For the case of molybdenum, we observed oxides from MoO3 - to Mo3Of-, for tantalum , TaO4 - to Ta5O 16- and...of Nb. Analogous to the niobium case, all three tantalum oxide anions lead to the same four sequential products. The results show that whenever there

  4. New Gel-Like Polymers as Selective Weak-Base Anion Exchangers

    PubMed Central

    Gierczyk, Błażej; Cegłowski, Michał; Zalas, Maciej

    2015-01-01

    A group of new anion exchangers, based on polyamine podands and of excellent ion-binding capacity, were synthesized. The materials were obtained in reactions between various poly(ethyleneamines) with glycidyl derivatives of cyclotetrasiloxane. The final polymeric, strongly cross-linked materials form gel-like solids. Their structures and interactions with anions adsorbed were studied by spectroscopic methods (CP-MAS NMR, FR-IR, UV-Vis). The sorption isotherms and kinetic parameters were determined for 29 anions. Materials studied show high ion capacity and selectivity towards some important anions, e.g., selenate(VI) or perrhenate. PMID:25946220

  5. Natural frequency of uniform and optimized tetrahedral truss platforms

    NASA Technical Reports Server (NTRS)

    Wu, K. Chauncey; Lake, Mark S.

    1994-01-01

    Qualitative and quantitative estimates for the fundamental frequency of uniform and optimized tetrahedral truss platforms are determined. A semiempirical equation is developed for the frequency of free-free uniform trusses as a function of member material properties, truss dimensions, and parasitic (nonstructural) mass fraction Mp/Mt. Optimized trusses with frequencies approximately two times those of uniform trusses are determined by varying the cross-sectional areas of member groups. Trusses with 3 to 8 rings, no parasitic mass, and member areas up to 25 times the minimum area are optimized. Frequencies computed for ranges of both Mp/Mt and the ratio of maximum area to minimum area are normalized to the frequency of a uniform truss with no parasitic mass. The normalized frequency increases with the number of rings, and both frequency and the ratio of maximum area to minimum area decrease with increasing Mp/Mt. Frequency improvements that are achievable with a limited number of member areas are estimated for a 3-ring truss by using Taguchi methods. Joint stiffness knockdown effects are also considered. Comparison of optimized and baseline uniform truss frequencies indicates that tailoring can significantly increase structural frequency; maximum gains occur for trusses with low values of Mp/Mt. This study examines frequency trends for ranges of structural parameters and may be used as a preliminary design guide.

  6. Analytical and Photogrammetric Characterization of a Planar Tetrahedral Truss

    NASA Technical Reports Server (NTRS)

    Wu, K. Chauncey; Adams, Richard R.; Rhodes, Marvin D.

    1990-01-01

    Future space science missions are likely to require near-optical quality reflectors which are supported by a stiff truss structure. This support truss should conform closely with its intended shape to minimize its contribution to the overall surface error of the reflector. The current investigation was conducted to evaluate the planar surface accuracy of a regular tetrahedral truss structure by comparing the results of predicted and measured node locations. The truss is a 2-ring hexagonal structure composed of 102 equal-length truss members. Each truss member is nominally 2 meters in length between node centers and is comprised of a graphite/epoxy tube with aluminum nodes and joints. The axial stiffness and the length variation of the truss components were determined experimentally and incorporated into a static finite element analysis of the truss. From this analysis, the root mean square (RMS) surface error of the truss was predicted to be 0.11 mm (0004 in). Photogrammetry tests were performed on the assembled truss to measure the normal displacements of the upper surface nodes and to determine if the truss would maintain its intended shape when subjected to repeated assembly. Considering the variation in the truss component lengths, the measures rms error of 0.14 mm (0.006 in) in the assembled truss is relatively small. The test results also indicate that a repeatable truss surface is achievable. Several potential sources of error were identified and discussed.

  7. TET peptidases: A family of tetrahedral complexes conserved in prokaryotes.

    PubMed

    Appolaire, Alexandre; Colombo, Matteo; Basbous, Hind; Gabel, Frank; Girard, E; Franzetti, Bruno

    2016-03-01

    The TET peptidases are large polypeptide destruction machines present among prokaryotes. They form 12-subunits hollow tetrahedral particles, and belong to the family of M42 metallo-peptidases. Structural characterization of various archaeal and bacterial complexes has revealed a unique mechanism of internal compartmentalization and peptide trafficking that distinguishes them from the other oligomeric peptidases. Different versions of the TET complex often co-exist in the cytosol of microorganisms. In depth enzymatic studies have revealed that they are non-processive cobalt-activated aminopeptidases and display contrasting substrate specificities based on the properties of the catalytic chambers. Recent studies have shed light on the assembly mechanism of homo and hetero-dodecameric TET complexes and shown that the activity of TET aminopeptidase towards polypeptides is coupled with its assembly process. These findings suggested a functional regulation based on oligomerization control in vivo. This review describes a current knowledge on M42 TET peptidases biochemistry and discuss their possible physiological roles. This article is a part of the Special Issue entitled: «A potpourri of proteases and inhibitors: from molecular toolboxes to signalling scissors».

  8. Adaptive hybrid prismatic-tetrahedral grids for viscous flows

    NASA Astrophysics Data System (ADS)

    Kallinderis, Yannis; Khawaja, Aly; McMorris, Harlan

    1995-03-01

    The paper presents generation of adaptive hybrid prismatic/tetrahedral grids for complex 3-D geometries including multi-body domains. The prisms cover the region close to each body's surface, while tetrahedra are created elsewhere. Two developments are presented for hybrid grid generation around complex 3-D geometries. The first is a new octree/advancing front type of method for generation of the tetrahedra of the hybrid mesh. The main feature of the present advancing front tetrahedra generator that is different from previous such methods is that it does not require the creation of a background mesh by the user for the determination of the grid-spacing and stretching parameters. These are determined via an automatically generated octree. The second development is an Automatic Receding Method (ARM) for treating the narrow gaps in between different bodies in a multiply-connected domain. This method is applied to a two-element wing case. A hybrid grid adaptation scheme that employs both h-refinement and redistribution strategies is developed to provide optimum meshes for viscous flow computations. Grid refinement is a dual adaptation scheme that couples division of tetrahedra, as well as 2-D directional division of prisms.

  9. Multi-Criterion Preliminary Design of a Tetrahedral Truss Platform

    NASA Technical Reports Server (NTRS)

    Wu, K. Chauncey

    1995-01-01

    An efficient method is presented for multi-criterion preliminary design and demonstrated for a tetrahedral truss platform. The present method requires minimal analysis effort and permits rapid estimation of optimized truss behavior for preliminary design. A 14-m-diameter, 3-ring truss platform represents a candidate reflector support structure for space-based science spacecraft. The truss members are divided into 9 groups by truss ring and position. Design variables are the cross-sectional area of all members in a group, and are either 1, 3 or 5 times the minimum member area. Non-structural mass represents the node and joint hardware used to assemble the truss structure. Taguchi methods are used to efficiently identify key points in the set of Pareto-optimal truss designs. Key points identified using Taguchi methods are the maximum frequency, minimum mass, and maximum frequency-to-mass ratio truss designs. Low-order polynomial curve fits through these points are used to approximate the behavior of the full set of Pareto-optimal designs. The resulting Pareto-optimal design curve is used to predict frequency and mass for optimized trusses. Performance improvements are plotted in frequency-mass (criterion) space and compared to results for uniform trusses. Application of constraints to frequency and mass and sensitivity to constraint variation are demonstrated.

  10. Adaptive hybrid prismatic-tetrahedral grids for viscous flows

    NASA Technical Reports Server (NTRS)

    Kallinderis, Yannis; Khawaja, Aly; Mcmorris, Harlan

    1995-01-01

    The paper presents generation of adaptive hybrid prismatic/tetrahedral grids for complex 3-D geometries including multi-body domains. The prisms cover the region close to each body's surface, while tetrahedra are created elsewhere. Two developments are presented for hybrid grid generation around complex 3-D geometries. The first is a new octree/advancing front type of method for generation of the tetrahedra of the hybrid mesh. The main feature of the present advancing front tetrahedra generator that is different from previous such methods is that it does not require the creation of a background mesh by the user for the determination of the grid-spacing and stretching parameters. These are determined via an automatically generated octree. The second development is an Automatic Receding Method (ARM) for treating the narrow gaps in between different bodies in a multiply-connected domain. This method is applied to a two-element wing case. A hybrid grid adaptation scheme that employs both h-refinement and redistribution strategies is developed to provide optimum meshes for viscous flow computations. Grid refinement is a dual adaptation scheme that couples division of tetrahedra, as well as 2-D directional division of prisms.

  11. Angular rigidity in tetrahedral network glasses with changing composition

    NASA Astrophysics Data System (ADS)

    Bauchy, M.; Micoulaut, M.; Celino, M.; Le Roux, S.; Boero, M.; Massobrio, C.

    2011-08-01

    A set of oxide and chalcogenide tetrahedral glasses is investigated using molecular dynamics simulations. We show that the changes in the Ge composition affect mostly bending around germanium in binary Ge-Se systems, leaving Se-centered bending almost unchanged. In contrast, the corresponding Se twisting (quantified by the dihedral angle) depends on the Ge composition and is reduced when the system becomes rigid. It is also shown that angles involving the fourth neighbor around Ge is found to change when the system enters the stressed rigid phase. The same analysis reveals that unlike stoichiometric selenides such as GeSe2 and SiSe2, germania and silica display large standard deviations in the bond angle distributions. Within bond-bending constraints theory, this pattern can be interpreted as a manifestation of broken (i.e., ineffective) oxygen bond-bending constraints, whereas the silicon and germanium bending in oxides is found to be similar to the one found in flexible and intermediate Ge-Se systems. Our results establish the atomic-scale foundations of the phenomenological rigidity theory, thereby profoundly extending its significance and impact on the structural description of network glasses.

  12. Superlattice Quantum Dots of Self-assembled Tetrahedral Nanocrystals

    NASA Astrophysics Data System (ADS)

    Wang, Z. L.; Yin, J. S.

    1998-03-01

    Size and shape selected CoO nanocrystals dominated by tetrahedral shape have been synthesized and assembled to form superlattices with long-range translation order and short-range orientation order [1]. The crystallography of self-assembled nanocrystal superlattices (NCSs) is determined not only by the size of the nanocrystals and the length of the passivation thiolates, but by the shape of the nanocrystals. The structure of the nanocrystals are determined by high-resolution transmission electron microscopy (TEM). A model is suggested to explain the observed orientation order and the result supports that the thiolates molecules distributed on the nanocrystal surfaces form bundles, and the nanocrystals are assembled in such a way that the bundles tend to fill the entire space. The stability of the NCSs has been examined in-situ using TEM. The result suggests the strong effect of the substrate on NCSs. [1] J.S. Yin and Z.L. Wang, Phys. Rev. Lett., 79 (No. 13) (1997) 2570-2573. [2] J.S. Yin and Z.L. Wang, J. Phys. Chem., 101 (1997) 8979-8983.

  13. Theoretical Studies of Routes to Synthesis of Tetrahedral N4

    NASA Technical Reports Server (NTRS)

    Lee, Timothy J.; Dateo, Christopher E.

    2007-01-01

    A paper [Chem. Phys. Lett. 345, 295 (2001)] describes theoretical studies of excited electronic states of nitrogen molecules, with a view toward utilizing those states in synthesizing tetrahedral N4, or Td N4 a metastable substance under consideration as a high-energy-density rocket fuel. Several ab initio theoretical approaches were followed in these studies, including complete active space self-consistent field (CASSCF), state-averaged CASSCF (SA-CASSCF), singles configuration interaction (CIS), CIS with second-order and third-order correlation corrections [CIS(D) and CIS(3)], and linear response singles and doubles coupled-cluster (LRCCSD). Standard double zeta polarized and triple zeta double polarized one-particle basis sets were used. The CASSCF calculations overestimated the excitation energies, while SACASSCF calculations partly corrected these overestimates. The accuracy of the CIS calculations varied, depending on the particular state, while the CIS(D), CIS(3), and LRCCSD results were in generally good agreement. The energies of the lowest six excited singlet states of Td N4 as calculated by the LRCCSD were compared with the energies of possible excited states of N2 + N2 fragments, leading to the conclusion that the most likely route for synthesis of Td N4 would involve a combination of two bound quintet states of N2.

  14. Intraframework migration of tetrahedral atoms in a zeolite.

    PubMed

    Shin, Jiho; Ahn, Nak Ho; Camblor, Miguel A; Cho, Sung June; Hong, Suk Bong

    2014-08-18

    The transformation from a disordered into an ordered version of the zeolite natrolite occurs on prolonged heating of this material in the crystallizing medium, but not if the mother liquor is replaced by water or an alkaline solution. This process occurs for both aluminosilicate and gallosilicate analogues of natrolite. In cross experiments, the disordered Al-containing (or Ga-containing) analogue is heated while in contact with the mother liquor of the opposite analogue, that is, the Ga-containing (or Al-containing) liquor. Therefore, strong evidence for the mechanism of the ordering process was obtained, which was thus proposed to proceed by intraframework migration of tetrahedral atoms without diffusion along the pores. Migration is first triggered, then fuelled by surface rearrangement through reactions with the mother liquor, and stops when an almost fully ordered state is attained. Classical dissolution-recrystallization and Ostwald ripening processes do not appear to be relevant for this phase transformation. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Connectivity, dynamics, and structure in a tetrahedral network liquid.

    PubMed

    Roldán-Vargas, Sándalo; Rovigatti, Lorenzo; Sciortino, Francesco

    2017-01-04

    We report a detailed computational study by Brownian dynamics simulations of the structure and dynamics of a liquid of patchy particles which forms an amorphous tetrahedral network upon decreasing the temperature. The highly directional particle interactions allow us to investigate the system connectivity by discriminating the total set of particles into different populations according to a penta-modal distribution of bonds per particle. With this methodology we show how the particle bonding process is not randomly independent but it manifests clear bond correlations at low temperatures. We further explore the dynamics of the system in real space and establish a clear relation between particle mobility and particle connectivity. In particular, we provide evidence of anomalous diffusion at low temperatures and reveal how the dynamics is affected by the short-time hopping motion of the weakly bounded particles. Finally we widely investigate the dynamics and structure of the system in Fourier space and identify two quantitatively similar length scales, one dynamic and the other static, which increase upon cooling the system and reach distances of the order of few particle diameters. We summarize our findings in a qualitative picture where the low temperature regime of the viscoelastic liquid is understood in terms of an evolving network of long time metastable cooperative domains of particles.

  16. Tetrahedral Arrangements of Perylene Bisimide Columns via Supramolecular Orientational Memory.

    PubMed

    Sahoo, Dipankar; Peterca, Mihai; Aqad, Emad; Partridge, Benjamin E; Heiney, Paul A; Graf, Robert; Spiess, Hans W; Zeng, Xiangbing; Percec, Virgil

    2017-01-24

    Chiral, shape, and liquid crystalline memory effects are well-known to produce commercial macroscopic materials with important applications as springs, sensors, displays, and memory devices. A supramolecular orientational memory effect that provides complex nanoscale arrangements was only recently reported. This supramolecular orientational memory was demonstrated to preserve the molecular orientation and packing within supramolecular units of a self-assembling cyclotriveratrylene crown at the nanoscale upon transition between its columnar hexagonal and Pm3̅n cubic periodic arrays. Here we report the discovery of supramolecular orientational memory in a dendronized perylene bisimide (G2-PBI) that self-assembles into tetrameric crowns and subsequently self-organizes into supramolecular columns and spheres. This supramolecular orientation memory upon transition between columnar hexagonal and body-centered cubic (BCC) mesophases preserves the 3-fold cubic [111] orientations rather than the 4-fold [100] axes, generating an unusual tetrahedral arrangement of supramolecular columns. These results indicate that the supramolecular orientational memory concept may be general for periodic arrays of self-assembling dendrons and dendrimers as well as for other periodic and quasiperiodic nanoscale organizations comprising supramolecular spheres, generated from other organized complex soft matter including block copolymers and surfactants.

  17. A suitable low-order, eight-node tetrahedral finite element for solids

    SciTech Connect

    Key, S.W.; Heinstein, M.S.; Stone, C.M.; Mello, F.J.; Blanford, M.L.; Budge, K.G.

    1998-03-01

    To use the all-tetrahedral mesh generation existing today, the authors have explored the creation of a computationally efficient eight-node tetrahedral finite element (a four-node tetrahedral finite element enriched with four mid-face nodal points). The derivation of the element`s gradient operator, studies in obtaining a suitable mass lumping, and the element`s performance in applications are presented. In particular they examine the eight-node tetrahedral finite element`s behavior in longitudinal plane wave propagation, in transverse cylindrical wave propagation, and in simulating Taylor bar impacts. The element samples only constant strain states and, therefore, has 12 hour-glass modes. In this regard it bears similarities to the eight-node, mean-quadrature hexahedral finite element. Comparisons with the results obtained from the mean-quadrature eight-node hexahedral finite element and the four-node tetrahedral finite element are included. Given automatic all-tetrahedral meshing, the eight-node, constant-strain tetrahedral finite element is a suitable replacement for the eight-node hexahedral finite element in those cases where mesh generation requires an inordinate amount of user intervention and direction to obtain acceptable mesh properties.

  18. Anionic fluoroquinolones as antibacterials against biofilm-producing Pseudomonas aeruginosa.

    PubMed

    Long, Timothy E; Keding, Lexie C; Lewis, Demetria D; Anstead, Michael I; Withers, T Ryan; Yu, Hongwei D

    2016-02-15

    Pseudomonas aeruginosa is a common biofilm-forming bacterial pathogen implicated in diseases of the lungs. The extracellular polymeric substances (EPS) of respiratory Pseudomonas biofilms are largely comprised of anionic molecules such as rhamnolipids and alginate that promote a mucoid phenotype. In this Letter, we examine the ability of negatively-charged fluoroquinolones to transverse the EPS and inhibit the growth of mucoid P. aeruginosa. Anionic fluoroquinolones were further compared with standard antibiotics via a novel microdiffusion assay to evaluate drug penetration through pseudomonal alginate and respiratory mucus from a patient with cystic fibrosis.

  19. A finite element boundary integral formulation for radiation and scattering by cavity antennas using tetrahedral elements

    NASA Technical Reports Server (NTRS)

    Gong, J.; Volakis, J. L.; Chatterjee, A.; Jin, J. M.

    1992-01-01

    A hybrid finite element boundary integral formulation is developed using tetrahedral and/or triangular elements for discretizing the cavity and/or aperture of microstrip antenna arrays. The tetrahedral elements with edge based linear expansion functions are chosen for modeling the volume region and triangular elements are used for discretizing the aperture. The edge based expansion functions are divergenceless thus removing the requirement to introduce a penalty term and the tetrahedral elements permit greater geometrical adaptability than the rectangular bricks. The underlying theory and resulting expressions are discussed in detail together with some numerical scattering examples for comparison and demonstration.

  20. Anion-π catalysis.

    PubMed

    Zhao, Yingjie; Beuchat, César; Domoto, Yuya; Gajewy, Jadwiga; Wilson, Adam; Mareda, Jiri; Sakai, Naomi; Matile, Stefan

    2014-02-05

    The introduction of new noncovalent interactions to build functional systems is of fundamental importance. We here report experimental and theoretical evidence that anion-π interactions can contribute to catalysis. The Kemp elimination is used as a classical tool to discover conceptually innovative catalysts for reactions with anionic transition states. For anion-π catalysis, a carboxylate base and a solubilizer are covalently attached to the π-acidic surface of naphthalenediimides. On these π-acidic surfaces, transition-state stabilizations up to ΔΔGTS = 31.8 ± 0.4 kJ mol(-1) are found. This value corresponds to a transition-state recognition of KTS = 2.7 ± 0.5 μM and a catalytic proficiency of 3.8 × 10(5) M(-1). Significantly increasing transition-state stabilization with increasing π-acidity of the catalyst, observed for two separate series, demonstrates the existence of "anion-π catalysis." In sharp contrast, increasing π-acidity of the best naphthalenediimide catalysts does not influence the more than 12 000-times weaker substrate recognition (KM = 34.5 ± 1.6 μM). Together with the disappearance of Michaelis-Menten kinetics on the expanded π-surfaces of perylenediimides, this finding supports that contributions from π-π interactions are not very important for anion-π catalysis. The linker between the π-acidic surface and the carboxylate base strongly influences activity. Insufficient length and flexibility cause incompatibility with saturation kinetics. Moreover, preorganizing linkers do not improve catalysis much, suggesting that the ideal positioning of the carboxylate base on the π-acidic surface is achieved by intramolecular anion-π interactions rather than by an optimized structure of the linker. Computational simulations are in excellent agreement with experimental results. They confirm, inter alia, that the stabilization of the anionic transition states (but not the neutral ground states) increases with the π-acidity of the

  1. Dynamical Instability Causes the Demise of a Supercooled Tetrahedral Liquid

    NASA Astrophysics Data System (ADS)

    Gautam, Arvind Kumar; Pingua, Nandlal; Goyal, Aashish; Apte, Pankaj A.

    2017-09-01

    We investigate the relaxation mechanism of a supercooled tetrahedral liquid at its limit of stability using isothermal isobaric ( NPT) Monte Carlo simulations. In similarity with systems which are far from equilibrium but near the onset of jamming (O'Hern et al. in Phys Rev Lett 93:165702, 2004), we find that the relaxation is characterized by two time-scales: the decay of long-wavelength (slow) fluctuations of potential energy is controlled by the slope [partial (G/N)/partial φ ] of the Gibbs free energy ( G) at a unique value of per particle potential energy φ = φ _{mid}. The short-wavelength (fast) fluctuations are controlled by the bath temperature T. The relaxation of the supercooled liquid is initiated with a dynamical crossover after which the potential energy fluctuations are biased towards values progressively lesser than φ _{mid}. The dynamical crossover leads to the change of time-scale, i.e., the decay of long-wavelength potential energy fluctuations (intermediate stage of relaxation). Because of the condition [partial ^2 (G/N)/partial φ ^2 = 0] at φ = φ _{mid}, the slope [partial (G/N)/partial φ ] has a unique value and governs the intermediate stage of relaxation, which ends just after the crossover. In the subsequent stage, there is a relatively rapid crystallization due to lack of long-wavelength fluctuations and the instability at φ _{mid}, i.e., the condition that G decreases as configurations with potential energies lower than φ _{mid} are accessed. The dynamical crossover point and the associated change in the time-scale of fluctuations is found to be consistent with the previous studies.

  2. Low-energy tetrahedral polymorphs of carbon, silicon, and germanium

    NASA Astrophysics Data System (ADS)

    Mujica, Andrés; Pickard, Chris J.; Needs, Richard J.

    2015-06-01

    Searches for low-energy tetrahedral polymorphs of carbon and silicon have been performed using density functional theory computations and the ab initio random structure searching approach. Several of the hypothetical phases obtained in our searches have enthalpies that are lower or comparable to those of other polymorphs of group 14 elements that have either been experimentally synthesized or recently proposed as the structure of unknown phases obtained in experiments, and should thus be considered as particularly interesting candidates. A structure of P b a m symmetry with 24 atoms in the unit cell was found to be a low-energy, low-density metastable polymorph in carbon, silicon, and germanium. In silicon, P b a m is found to have a direct band gap at the zone center with an estimated value of 1.4 eV, which suggests applications as a photovoltaic material. We have also found a low-energy chiral framework structure of P 41212 symmetry with 20 atoms per cell containing fivefold spirals of atoms, whose projected topology is that of the so-called Cairo-type two-dimensional pentagonal tiling. We suggest that P 41212 is a likely candidate for the structure of the unknown phase XIII of silicon. We discuss P b a m and P 41212 in detail, contrasting their energetics and structures with those of other group 14 elements, particularly the recently proposed P 42/n c m structure, for which we also provide a detailed interpretation as a network of tilted diamondlike tetrahedra.

  3. Covalent bonding of polycations to small polymeric particles

    NASA Technical Reports Server (NTRS)

    Rembaum, A.

    1975-01-01

    Process produces small spherical polymeric particles which have polycations bound to them. In emulsion form, particles present large positively charged surface which is available to absorb polyanions. This properly can be used in removing heparin from blood or bile acids from the digestive tract. Other anions, such as DNA and RNA, can also be removed from aqueous solutions.

  4. Optical and magnetic properties of transition-metal ions in tetrahedral and octahedral compounds

    NASA Astrophysics Data System (ADS)

    Li, Huifang; Wang, Huaiqian; Kuang, Xiaoyu

    2011-10-01

    This paper presents the complete energy matrix of the 3d2 system containing the electron-electron interaction, the ligand-field interaction, the spin-orbit coupling interaction, and the Zeeman interaction, in which the optical spectra and g-factor of V3+and Ti2+ ions in the series of tetrahedral AIIBVI (AII=Zn, Cd, BVI=S, Se, Te) semiconductor materials are determined. In the investigation of the optical and magnetic properties of these transition-metal ions in the tetrahedral coordination complexes, we compared the data obtained from the transition-metal ions in the tetrahedral coordination complexes with those obtained from the corresponding ions in the octahedral ones, and found that the tetrahedral complexes have weaker crystal-field strength, inverse energy level ordering and stronger covalence effect.

  5. Polymerization of perfluorobutadiene

    NASA Technical Reports Server (NTRS)

    Newman, J.; Toy, M. S.

    1970-01-01

    Diisopropyl peroxydicarbonate dissolved in liquid perfluorobutadiene is conducted in a sealed vessel at the autogenous pressure of polymerization. Reaction temperature, ratio of catalyst to monomer, and amount of agitation determine degree of polymerization and product yield.

  6. Comparison of hexahedral and tetrahedral elements in finite element analysis of the foot and footwear.

    PubMed

    Tadepalli, Srinivas C; Erdemir, Ahmet; Cavanagh, Peter R

    2011-08-11

    Finite element analysis has been widely used in the field of foot and footwear biomechanics to determine plantar pressures as well as stresses and strains within soft tissue and footwear materials. When dealing with anatomical structures such as the foot, hexahedral mesh generation accounts for most of the model development time due to geometric complexities imposed by branching and embedded structures. Tetrahedral meshing, which can be more easily automated, has been the approach of choice to date in foot and footwear biomechanics. Here we use the nonlinear finite element program Abaqus (Simulia, Providence, RI) to examine the advantages and disadvantages of tetrahedral and hexahedral elements under compression and shear loading, material incompressibility, and frictional contact conditions, which are commonly seen in foot and footwear biomechanics. This study demonstrated that for a range of simulation conditions, hybrid hexahedral elements (Abaqus C3D8H) consistently performed well while hybrid linear tetrahedral elements (Abaqus C3D4H) performed poorly. On the other hand, enhanced quadratic tetrahedral elements with improved stress visualization (Abaqus C3D10I) performed as well as the hybrid hexahedral elements in terms of contact pressure and contact shear stress predictions. Although the enhanced quadratic tetrahedral element simulations were computationally expensive compared to hexahedral element simulations in both barefoot and footwear conditions, the enhanced quadratic tetrahedral element formulation seems to be very promising for foot and footwear applications as a result of decreased labor and expedited model development, all related to facilitated mesh generation. Copyright © 2011. Published by Elsevier Ltd.

  7. Shape effects on the random-packing density of tetrahedral particles.

    PubMed

    Zhao, Jian; Li, Shuixiang; Jin, Weiwei; Zhou, Xuan

    2012-09-01

    Regular tetrahedra have been demonstrated recently giving high packing density in random configurations. However, it is unknown whether the random-packing density of tetrahedral particles with other shapes can reach an even higher value. A numerical investigation on the random packing of regular and irregular tetrahedral particles is carried out. Shape effects of rounded corner, eccentricity, and height on the packing density of tetrahedral particles are studied. Results show that altering the shape of tetrahedral particles by rounding corners and edges, by altering the height of one vertex, or by lateral displacement of one vertex above its opposite face, all individually have the effect of reducing the random-packing density. In general, the random-packing densities of irregular tetrahedral particles are lower than that of regular tetrahedra. The ideal regular tetrahedron should be the shape which has the highest random-packing density in the family of tetrahedra, or even among convex bodies. An empirical formula is proposed to describe the rounded corner effect on the packing density, and well explains the density deviation of tetrahedral particles with different roundness ratios. The particles in the simulations are verified to be randomly packed by studying the pair correlation functions, which are consistent with previous results. The spherotetrahedral particle model with the relaxation algorithm is effectively applied in the simulations.

  8. List-mode image reconstruction for positron emission tomography using tetrahedral voxels

    NASA Astrophysics Data System (ADS)

    Gillam, John E.; Angelis, Georgios I.; Meikle, Steven R.

    2016-09-01

    Image space decomposition based on tetrahedral voxels are interesting candidates for use in emission tomography. Tetrahedral voxels provide many of the advantages of point clouds with irregular spacing, such as being intrinsically multi-resolution, yet they also serve as a volumetric partition of the image space and so are comparable to more standard cubic voxels. Additionally, non-rigid displacement fields can be applied to the tetrahedral mesh in a straight-forward manner. So far studies incorporating tetrahedral decomposition of the image space have concentrated on pre-calculated, node-based, system matrix elements which reduces the flexibility of the tetrahedral approach and the capacity to accurately define regions of interest. Here, a list-mode on-the-fly calculation of the system matrix elements is described using a tetrahedral decomposition of the image space and volumetric elements—voxels. The algorithm is demonstrated in the context of awake animal PET which may require both rigid and non-rigid motion compensation, as well as quantification within small regions of the brain. This approach allows accurate, event based, motion compensation including non-rigid deformations.

  9. Electronic structures of filled tetrahedral semiconductors LiMgN and LiZnN: conduction band distortion

    NASA Astrophysics Data System (ADS)

    Yu, L. H.; Yao, K. L.; Liu, Z. L.

    2004-12-01

    The band structures of the filled tetrahedral semiconductors LiMgN and LiZnN, viewed as the zinc-blende (MgN) - and (ZnN) - lattices partially filled with He-like Li + ion interstitials, were studied using the full-potential linearized augmented plane wave method (FP-LAPW) within density functional theory. The conduction band distortions of LiMgN and LiZnN, compared to their “parent” zinc-blende analog AlN and GaN, are discussed. It was found that the insertion of Li + ions at the interstitial sites near the cation or anion pushes the conduction band minimum of the X point in the Brillouin zone upward, relative to that of the Γ point, for both (MgN) - and (ZnN) - lattices (the valence band maximum is at Γ for AlN, GaN, LiMgN, and LiZnN), which provides a method to convert a zinc-blende indirect gap semiconductor into a direct gap material, but the conduction band distortion of the β phase (Li + near the cation) is quite stronger than that of the α phase (Li + near the anion). The total energy calculations show the α phase to be more stable than the β phase for both LiMgN and LiZnN. The Li-N and Mg-N bonds exhibit a strong ionic character, whereas the Zn-N bond has a strong covalent character in LiMgN and LiZnN.

  10. Complex anion inclusion compounds: flexible anion-exchange materials.

    PubMed

    Williams, Edward R; Leithall, Rebecca M; Raja, Robert; Weller, Mark T

    2013-01-11

    Copper chloropyrophosphate frameworks have been synthesised with a wide variety of complex inorganic anions trapped in a large, flexible, one-dimensional pore, with anions including chloride, bromide, phosphate and the complex metal halo-anions PtCl(4)(2-), PdBr(4)(2-), CuCl(4)(2-) and AuCl(4)(-).

  11. Polymerization Reactor Engineering.

    ERIC Educational Resources Information Center

    Skaates, J. Michael

    1987-01-01

    Describes a polymerization reactor engineering course offered at Michigan Technological University which focuses on the design and operation of industrial polymerization reactors to achieve a desired degree of polymerization and molecular weight distribution. Provides a list of the course topics and assigned readings. (TW)

  12. Polymerization Reactor Engineering.

    ERIC Educational Resources Information Center

    Skaates, J. Michael

    1987-01-01

    Describes a polymerization reactor engineering course offered at Michigan Technological University which focuses on the design and operation of industrial polymerization reactors to achieve a desired degree of polymerization and molecular weight distribution. Provides a list of the course topics and assigned readings. (TW)

  13. A review of defects and disorder in multinary tetrahedrally bonded semiconductors [Defects and disorder in multinary tetrahedrally bonded semiconductors studied by experiment and theory

    DOE PAGES

    Baranowski, Lauryn L.; Zawadzki, Pawel; Lany, Stephan; ...

    2016-11-10

    Defects are critical to understanding the electronic properties of semiconducting compounds, for applications such as light-emitting diodes, transistors, photovoltaics, and thermoelectrics. In this review, we describe our work investigating defects in tetrahedrally bonded, multinary semiconductors, and discuss the place of our research within the context of publications by other groups. We applied experimental and theory techniques to understand point defects, structural disorder, and extended antisite defects in one semiconductor of interest for photovoltaic applications, Cu2SnS3. We contrast our findings on Cu2SnS3 with other chemically related Cu-Sn-S compounds, as well as structurally related compounds such as Cu2ZnSnS4 and Cu(In,Ga)Se2. We findmore » that evaluation of point defects alone is not sufficient to understand defect behavior in multinary tetrahedrally bonded semiconductors. In the case of Cu2SnS3 and Cu2ZnSnS4, structural disorder and entropy-driven cation clustering can result in nanoscale compositional inhomogeneities which detrimentally impact the electronic transport. Therefore, it is not sufficient to assess only the point defect behavior of new multinary tetrahedrally bonded compounds; effects such as structural disorder and extended antisite defects must also be considered. Altogether, this review provides a framework for evaluating tetrahedrally bonded semiconducting compounds with respect to their defect behavior for photovoltaic and other applications, and suggests new materials that may not be as prone to such imperfections.« less

  14. A novel open-framework copper borophosphate containing 1-D borophosphate anion with 10-MR windows and 12-MR channels.

    PubMed

    Feng, Yuquan; Li, Min; Fan, Huitao; Huang, Qunzeng; Qiu, Dongfang; Shi, Hengzhen

    2015-01-21

    A novel open-framework copper borophosphate, Na5KCu3[B9P6O33(OH)3]·H2O (), has been synthesised by a boric acid flux method. Its structure can be viewed as a 3-D open framework constructed by the connection of Cu(II)O6 octahedra and 1-D (4,4)-connected borophosphate anionic structures composed of trigonal-planar BO2(OH) groups, tetrahedral BO4 and PO4 groups. The compound not only features a novel borophosphate anionic partial structure containing 1-D 12-MR channels, but also exhibits ferromagnetic interactions and high catalytic activity for the oxidative degradation of chitosan.

  15. Polymerization initated at sidewalls of carbon nanotubes

    NASA Technical Reports Server (NTRS)

    Tour, James M. (Inventor); Hudson, Jared L. (Inventor); Krishnamoorti, Ramanan (Inventor); Yurekli, Koray (Inventor); Mitchell, Cynthia A. (Inventor)

    2011-01-01

    The present invention is directed to aryl halide (such as aryl bromide) functionalized carbon nanotubes that can be utilized in anionic polymerization processes to form polymer-carbon nanotube materials with improved dispersion ability in polymer matrices. In this process the aryl halide is reacted with an alkyllithium species or is reacted with a metal to replace the aryl-bromine bond with an aryl-lithium or aryl-metal bond, respectively. It has further been discovered that other functionalized carbon nanotubes, after deprotonation with a deprotonation agent, can similarly be utilized in anionic polymerization processes to form polymer-carbon nanotube materials. Additionally or alternatively, a ring opening polymerization process can be performed. The resultant materials can be used by themselves due to their enhanced strength and reinforcement ability when compared to their unbound polymer analogs. Additionally, these materials can also be blended with pre-formed polymers to establish compatibility and enhanced dispersion of nanotubes in otherwise hard to disperse matrices resulting in significantly improved material properties. The resultant polymer-carbon nanotube materials can also be used in drug delivery processes due to their improved dispersion ability and biodegradability, and can also be used for scaffolding to promote cellular growth of tissue.

  16. Photodetachment of Lanthanide Oxide Anions

    NASA Astrophysics Data System (ADS)

    Covington, A. M.; Emmons, E. D.; Kraus, R. G.; Thompson, J. S.; Calabrese, D.; Davis, V. T.

    2007-06-01

    Laser photodetached electron spectroscopy (LPES) has been used to study the structure and collision properties of lanthanide oxide anions including LaOn^- and CeOn^-. Preliminary photoelectron spectra from these anions will be presented along with ion beam production data from these and other lanthanide oxide anions.

  17. Hydrated hydride anion clusters

    NASA Astrophysics Data System (ADS)

    Lee, Han Myoung; Kim, Dongwook; Singh, N. Jiten; Kołaski, Maciej; Kim, Kwang S.

    2007-10-01

    On the basis of density functional theory (DFT) and high level ab initio theory, we report the structures, binding energies, thermodynamic quantities, IR spectra, and electronic properties of the hydride anion hydrated by up to six water molecules. Ground state DFT molecular dynamics simulations (based on the Born-Oppenheimer potential surface) show that as the temperature increases, the surface-bound hydride anion changes to the internally bound structure. Car-Parrinello molecular dynamics simulations are also carried out for the spectral analysis of the monohydrated hydride. Excited-state ab initio molecular dynamics simulations show that the photoinduced charge-transfer-to-solvent phenomena are accompanied by the formation of the excess electron-water clusters and the detachment of the H radical from the clusters. The dynamics of the detachment process of a hydrogen radical upon the excitation is discussed.

  18. Anion permselective membrane

    NASA Astrophysics Data System (ADS)

    Hodgdon, R. B.; Waite, W. A.; Alexander, S. S.

    1984-07-01

    Two polymer ion exchange membranes were synthesized to fulfill the needs of both electrical resistivity and anolyte/catholyte separation for utility load leveling utilizing the DOE/NASA mixed electrolyte REDOX battery. Both membranes were shown to meet mixed electrolyte utility load leveling criteria. Several modifications of an anion exchange membrane failed to meet utility load leveling REDOX battery criteria using the unmixed electrolyte REDOX cell.

  19. Anion permselective membrane

    NASA Technical Reports Server (NTRS)

    Hodgdon, R. B.; Waite, W. A.; Alexander, S. S.

    1984-01-01

    Two polymer ion exchange membranes were synthesized to fulfill the needs of both electrical resistivity and anolyte/catholyte separation for utility load leveling utilizing the DOE/NASA mixed electrolyte REDOX battery. Both membranes were shown to meet mixed electrolyte utility load leveling criteria. Several modifications of an anion exchange membrane failed to meet utility load leveling REDOX battery criteria using the unmixed electrolyte REDOX cell.

  20. Free Radical Polymerization of Styrene and Methyl Methacrylate in Various Room Temperature Ionic Liquids

    SciTech Connect

    Zhang, Hongwei; Hong, Kunlun; Mays, Jimmy

    2005-01-01

    Conventional free radical polymerization of styrene and methyl methacrylate was carried out in various room temperature ionic liquids (RTILs). The RTILs used in this research encompass a wide range of cations and anions. Typical cations include imidazolium, phosphonium, pyridinium, and pyrrolidinium; typical anions include amide, borate, chloride, imide, phosphate, and phosphinate. Reactions are faster and polymers obtained usually have higher molecular weights when compared to polymerizations carried out in volatile organic solvents under the same conditions. This shows that rapid rates of polymerization and high molecular weights are general features of conventional radical polymerizations in RTILs. Attempts to correlate the polarities and viscosities of the RTILs with the polymerization behavior fail to yield discernible trends.

  1. Solid polymeric electrolytes for lithium batteries

    DOEpatents

    Angell, Charles A.; Xu, Wu; Sun, Xiaoguang

    2006-03-14

    Novel conductive polyanionic polymers and methods for their preparion are provided. The polyanionic polymers comprise repeating units of weakly-coordinating anionic groups chemically linked to polymer chains. The polymer chains in turn comprise repeating spacer groups. Spacer groups can be chosen to be of length and structure to impart desired electrochemical and physical properties to the polymers. Preferred embodiments are prepared from precursor polymers comprising the Lewis acid borate tri-coordinated to a selected ligand and repeating spacer groups to form repeating polymer chain units. These precursor polymers are reacted with a chosen Lewis base to form a polyanionic polymer comprising weakly coordinating anionic groups spaced at chosen intervals along the polymer chain. The polyanionic polymers exhibit high conductivity and physical properties which make them suitable as solid polymeric electrolytes in lithium batteries, especially secondary lithium batteries.

  2. Implementation of tetrahedral-mesh geometry in Monte Carlo radiation transport code PHITS.

    PubMed

    Furuta, Takuya; Sato, Tatsuhiko; Han, Min; Yeom, Yeon; Kim, Chan; Brown, Justin; Bolch, Wesley

    2017-04-04

    A new function to treat tetrahedral-mesh geometry was implemented in the Particle and Heavy Ion Transport code Systems (PHITS). To accelerate the computational speed in the transport process, an original algorithm was introduced to initially prepare decomposition maps for the container box of the tetrahedral-mesh geometry. The computational performance was tested by conducting radiation transport simulations of 100 MeV protons and 1 MeV photons in a water phantom represented by tetrahedral mesh. The simulation was repeated with varying number of meshes and the required computational times were then compared with those of the conventional voxel representation. Our results show that the computational costs for each boundary crossing of the region mesh are essentially equivalent for both representations. This study suggests that the tetrahedral-mesh representation offers not only a flexible description of the transport geometry but also improvement of computational efficiency for the radiation transport. Due to the adaptability of tetrahedrons in both size and shape, dosimetrically equivalent objects can be represented by tetrahedrons with a much fewer number of meshes as compared its voxelized representation. Our study additionally included dosimetric calculations using a computational human phantom. A significant acceleration of the computational speed, about 4 times, was confirmed by the adoption of a tetrahedral mesh over the traditional voxel mesh geometry.

  3. Serine Protease Catalysis: A Computational Study of Tetrahedral Intermediates and Inhibitory Adducts.

    PubMed

    Ngo, Phong D; Mansoorabadi, Steven O; Frey, Perry A

    2016-08-04

    Peptide boronic acids and peptidyl trifluoromethyl ketones (TFKs) inhibit serine proteases by forming monoanionic, tetrahedral adducts to serine in the active sites. Investigators regard these adducts as analogs of monoanionic, tetrahedral intermediates. Density functional theory (DFT) calculations and fractional charge analysis show that tetrahedral adducts of model peptidyl TFKs are structurally and electrostatically very similar to corresponding tetrahedral intermediates. In contrast, the DFT calculations show the structures and electrostatic properties of analogous peptide boronate adducts to be significantly different. The peptide boronates display highly electrostatically positive boron, with correspondingly negative ligands in the tetrahedra. In addition, the computed boron-oxygen and boron-carbon bond lengths in peptide boronates (which are identical or very similar to the corresponding bonds in a peptide boronate adduct of α-lytic protease determined by X-ray crystallography at subangstrom resolution) are significantly longer than the corresponding bond lengths in model tetrahedral intermediates. Since protease-peptidyl TFKs incorporate low-barrier hydrogen bonds (LBHBs) between an active site histidine and aspartate, while the protease-peptide boronates do not, these data complement the spectroscopic and chemical evidence for the participation of LBHBs in catalysis by serine proteases. Moreover, while the potency of these classes of inhibitors can be correlated to the structures of the peptide moieties, the present results indicate that the strength of their bonds to serine contribute significantly to their inhibitory properties.

  4. Tetrahedral 4 α and 12C+α cluster structures in 16O

    NASA Astrophysics Data System (ADS)

    Kanada-En'yo, Yoshiko

    2017-09-01

    I have investigated structures of the ground and excited states of 16O with the method of variation after spin-parity projection in the antisymmetrized molecular dynamics model combined with the generator coordinate method of 12C+α cluster. The calculation reasonably reproduces the experimental energy spectra; E 2 , E 3 , E 4 , and I S 1 transitions; and α -decay properties. The formation of 4 α clusters has been confirmed from nucleon degrees of freedom in the AMD model without assuming the existence of any clusters. They form "tetrahedral" 4 α - and 12C+α cluster structures. The 12C+α structure constructs the Kπ=0+ band consisting of the 02+, 21+, and 41+ states and the Kπ=0- band of the 12-, 32-, and 51- states. The 01+, 31-, and 42+ states are assigned to the ground band constructed from the tetrahedral 4 α structure. The 01+ and 31- are approximately interpreted as Td band members with the ideal tetrahedral configuration. The ground-state 4 α correlation plays an important role in the enhancement of the E 3 transition strength to the 31-. The 42+ state is not the ideal Td member but constructed from a distorted tetrahedral 4 α structure. Moreover, significant state mixing of the tetrahedral 4 α and 12C+α cluster structures occurs between 41+ and 42+ states, indicating that the Td configuration of 4 α is rather fragile at Jπ=4+ .

  5. Implementation of tetrahedral-mesh geometry in Monte Carlo radiation transport code PHITS

    NASA Astrophysics Data System (ADS)

    Furuta, Takuya; Sato, Tatsuhiko; Han, Min Cheol; Yeom, Yeon Soo; Kim, Chan Hyeong; Brown, Justin L.; Bolch, Wesley E.

    2017-06-01

    A new function to treat tetrahedral-mesh geometry was implemented in the particle and heavy ion transport code systems. To accelerate the computational speed in the transport process, an original algorithm was introduced to initially prepare decomposition maps for the container box of the tetrahedral-mesh geometry. The computational performance was tested by conducting radiation transport simulations of 100 MeV protons and 1 MeV photons in a water phantom represented by tetrahedral mesh. The simulation was repeated with varying number of meshes and the required computational times were then compared with those of the conventional voxel representation. Our results show that the computational costs for each boundary crossing of the region mesh are essentially equivalent for both representations. This study suggests that the tetrahedral-mesh representation offers not only a flexible description of the transport geometry but also improvement of computational efficiency for the radiation transport. Due to the adaptability of tetrahedrons in both size and shape, dosimetrically equivalent objects can be represented by tetrahedrons with a much fewer number of meshes as compared its voxelized representation. Our study additionally included dosimetric calculations using a computational human phantom. A significant acceleration of the computational speed, about 4 times, was confirmed by the adoption of a tetrahedral mesh over the traditional voxel mesh geometry.

  6. Electron and Hole Transfer in Anion-Bound Chemically Amplified Resists Used in Extreme Ultraviolet Lithography

    NASA Astrophysics Data System (ADS)

    Komuro, Yoshitaka; Yamamoto, Hiroki; Utsumi, Yoshiyuki; Ohomori, Katsumi; Kozawa, Takahiro

    2013-01-01

    The uniformity of acid generator distribution and the length of acid diffusion are serious problems in the development of resist materials used for the 16 nm node and below. Anion-bound polymers in which the anion part of onium salts is polymerized have attracted much attention for solving these problems. In this study, the reaction mechanism of an anion-bound polymer in cyclohexanone was clarified using pulse radiolysis. The design of an efficient electron and hole transfer system is essential to the enhancement of resist performance.

  7. Electron and hole transfer in anion-bound chemically amplified resists used in extreme ultraviolet lithography

    NASA Astrophysics Data System (ADS)

    Komuro, Yoshitaka; Yamamoto, Hiroki; Utsumi, Yoshiyuki; Ohmori, Katsumi; Kozawa, Takahiro

    2014-04-01

    The uniformity of acid generator distribution and the length of acid diffusion are serious problems in the development of resist materials used for the 16nm node and below. Anion-bound polymers in which the anion part of onium salts is polymerized have attracted much attention for solving these problems. In this study, the reaction mechanism of an anion-bound polymer in cyclohexanone was clarified using pulse radiolysis. The design of an efficient electron and hole transfer system is essential to the enhancement of resist performance.

  8. Haldane-Hubbard Mott Insulator: From Tetrahedral Spin Crystal to Chiral Spin Liquid

    NASA Astrophysics Data System (ADS)

    Hickey, Ciarán; Cincio, Lukasz; Papić, Zlatko; Paramekanti, Arun

    2016-04-01

    Motivated by cold atom experiments on Chern insulators, we study the honeycomb lattice Haldane-Hubbard Mott insulator of spin-1 /2 fermions using exact diagonalization and density matrix renormalization group methods. We show that this model exhibits various chiral magnetic orders including a wide regime of triple-Q tetrahedral order. Incorporating third-neighbor hopping frustrates and ultimately melts this tetrahedral spin crystal. From analyzing the low energy spectrum, many-body Chern numbers, entanglement spectra, and modular matrices, we identify the molten state as a chiral spin liquid (CSL) with gapped semion excitations. We formulate and study the Chern-Simons-Higgs field theory of the exotic CSL-to-tetrahedral spin crystallization transition.

  9. Haldane-Hubbard Mott Insulator: From Tetrahedral Spin Crystal to Chiral Spin Liquid.

    PubMed

    Hickey, Ciarán; Cincio, Lukasz; Papić, Zlatko; Paramekanti, Arun

    2016-04-01

    Motivated by cold atom experiments on Chern insulators, we study the honeycomb lattice Haldane-Hubbard Mott insulator of spin-1/2 fermions using exact diagonalization and density matrix renormalization group methods. We show that this model exhibits various chiral magnetic orders including a wide regime of triple-Q tetrahedral order. Incorporating third-neighbor hopping frustrates and ultimately melts this tetrahedral spin crystal. From analyzing the low energy spectrum, many-body Chern numbers, entanglement spectra, and modular matrices, we identify the molten state as a chiral spin liquid (CSL) with gapped semion excitations. We formulate and study the Chern-Simons-Higgs field theory of the exotic CSL-to-tetrahedral spin crystallization transition.

  10. Reordering between tetrahedral and octahedral sites in ultrathin magnetite films grown on MgO(001)

    SciTech Connect

    Bertram, F.; Deiter, C.; Schemme, T.; Jentsch, S.; Wollschlaeger, J.

    2013-05-14

    Magnetite ultrathin films were grown using different deposition rates and substrate temperatures. The structure of these films was studied using (grazing incidence) x-ray diffraction, while their surface structure was characterized by low energy electron diffraction. In addition to that, we performed x-ray photoelectron spectroscopy and magneto optic Kerr effect measurements to probe the stoichiometry of the films as well as their magnetic properties. The diffraction peaks of the inverse spinel structure, which originate exclusively from Fe ions on tetrahedral sites are strongly affected by the preparation conditions, while the octahedral sites remain almost unchanged. With both decreasing deposition rate as well as decreasing substrate temperature, the integrated intensity of the diffraction peaks originating exclusively from Fe on tetrahedral sites is decreasing. We propose that the ions usually occupying tetrahedral sites in magnetite are relocated to octahedral vacancies. Ferrimagnetic behaviour is only observed for well ordered magnetite films.

  11. A review of defects and disorder in multinary tetrahedrally bonded semiconductors [Defects and disorder in multinary tetrahedrally bonded semiconductors studied by experiment and theory

    SciTech Connect

    Baranowski, Lauryn L.; Zawadzki, Pawel; Lany, Stephan; Toberer, Eric S.; Zakutayev, Andriy

    2016-11-10

    Defects are critical to understanding the electronic properties of semiconducting compounds, for applications such as light-emitting diodes, transistors, photovoltaics, and thermoelectrics. In this review, we describe our work investigating defects in tetrahedrally bonded, multinary semiconductors, and discuss the place of our research within the context of publications by other groups. We applied experimental and theory techniques to understand point defects, structural disorder, and extended antisite defects in one semiconductor of interest for photovoltaic applications, Cu2SnS3. We contrast our findings on Cu2SnS3 with other chemically related Cu-Sn-S compounds, as well as structurally related compounds such as Cu2ZnSnS4 and Cu(In,Ga)Se2. We find that evaluation of point defects alone is not sufficient to understand defect behavior in multinary tetrahedrally bonded semiconductors. In the case of Cu2SnS3 and Cu2ZnSnS4, structural disorder and entropy-driven cation clustering can result in nanoscale compositional inhomogeneities which detrimentally impact the electronic transport. Therefore, it is not sufficient to assess only the point defect behavior of new multinary tetrahedrally bonded compounds; effects such as structural disorder and extended antisite defects must also be considered. Altogether, this review provides a framework for evaluating tetrahedrally bonded semiconducting compounds with respect to their defect behavior for photovoltaic and other applications, and suggests new materials that may not be as prone to such imperfections.

  12. Rational design and construction of the first tetrahedral net with photoluminescent Cu4I4 cubane cluster as the tetrahedral node.

    PubMed

    Hu, Sheng; Tong, Ming-Liang

    2005-04-07

    Solvothermal reaction of CuI with flexible 1,3-bis(4-pyridyl)propane generated the first three-dimensional coordination polymer constructed with the rigid tetrahedrally connected Cu4I4 cluster unit. The net is a rare chiral triple-interpenetrated, quartz net with of vertex symbol 6(4).8(2). The solid-state luminescence spectrum displays a strong red emission band at room temperature (lambdamax= 601 nm), characteristic of the Cu4I4 cluster centers.

  13. Advancements in Anion Exchange Membrane Cations

    SciTech Connect

    Sturgeon, Matthew R.; Long, Hai; Park, Andrew M.; Pivovar, Bryan S.

    2015-10-15

    Anion-exchange membrane fuel cells (AME-FCs) are of increasingly popular interest as they enable the use of non-Pt fuel cell catalysts, the primary cost limitation of proton exchange membrane fuel cells. Benzyltrimethyl ammonium (BTMA) is the standard cation that has historically been utilized as the hydroxide conductor in AEMs. Herein we approach AEMs from two directions. First and foremost we study the stability of several different cations in a hydroxide solution at elevated temperatures. We specifically targeted BTMA and methoxy and nitro substituted BTMA. We've also studied the effects of adding an akyl spacer units between the ammonium cation and the phenyl group. In the second approach we use computational studies to predict stable ammonium cations, which are then synthesized and tested for stability. Our unique method to study cation stability in caustic conditions at elevated temperatures utilizes Teflon Parr reactors suitable for use under various temperatures and cation concentrations. NMR analysis was used to determine remaining cation concentrations at specific time points with GCMS analysis verifying product distribution. We then compare the experimental results with calculated modeling stabilities. Our studies show that the electron donating methoxy groups slightly increase stability (compared to that of BTMA), while the electron withdrawing nitro groups greatly decrease stability in base. These results give insight into possible linking strategies to be employed when tethering a BTMA like ammonium cation to a polymeric backbone; thus synthesizing an anion exchange membrane.

  14. Mixed Anion Heterostructure Materials

    DTIC Science & Technology

    2004-10-01

    data presented Sb(g) Sb(ads) Sb(s) Kads D (1) (2)Very low + GaAs no reaction ( 3 ) kexch 33 for As2 which indicates that the...Kads D (1) (2) ( 3 ) Anion Exchange kexch (4) Isoelectronic AsSb formation Favoured by As4 +As GaAsySb1-y + Sby(s) GaSb1-y + AsSby(s) +As kiso (5...experiment implemented for this investigation provided a basis for modeling the P(g) P(ads) P(s) + GaAs Kads D (1) (2) ( 3 ) kexch (4) +P GaPyAs1-y

  15. Anion permselective membrane

    NASA Technical Reports Server (NTRS)

    Hodgdon, R. B.; Waite, W. A.

    1980-01-01

    The efforts on the synthesis of polymer anion redox membranes were mainly concentrated in two areas, membrane development and membrane fabrication. Membrane development covered the preparation and evaluation of experimental membranes systems with improved resistance stability and/or lower permeability. Membrane fabrication covered the laboratory scale production of prime candidate membranes in quantities of up to two hundred and sizes up to 18 inches x 18 inches (46 cm x 46 cm). These small (10 in x 11 in) and medium sized membranes were mainly for assembly into multicell units. Improvements in processing procedures and techniques for preparing such membrane sets lifted yields to over 90 percent.

  16. Transformational part-count in layered octahedral-tetrahedral truss configurations

    NASA Technical Reports Server (NTRS)

    Lalvani, Haresh

    1990-01-01

    The number of component part (nodes, struts and panels) termed part count, is an important factor in the design, manufacture, and assembly of modular space structures. Part count expressions are presented for a variety of profiles derived from the layered octahedral-tetrahedral truss configuration. Referred to as the tetrahedral truss in the NASA projects, this specific geometry has been used in several missions. The general expressions presented here transforms to others as one profile changes to another. Such transformational part count relations provide a measure of flexibility and generality, and may be useful when dealing with a wider range of geometric configurations.

  17. Pseudorotation in fullerene anions

    NASA Astrophysics Data System (ADS)

    Dunn, Janette L.; Hands, Ian D.; Bates, Colin A.

    2007-07-01

    Jahn-Teller (JT) problems are often characterised by an adiabatic potential energy surface (APES) containing either a set of isoenergetic wells or a trough of equivalent-energy points, which may be warped by higher-order coupling terms or anisotropic effects. In all three cases, the JT effect will be dynamic. Either tunnelling between the wells or rotation (of a distortion) around the trough will restore the original symmetry of the system. This motion is referred to as pseudorotation. It should be possible to observe a JT system in a distorted geometry if measurements are made on a sufficiently short timescale. In various cubic systems, this timescale has been calculated to be the order of picoseconds. Such timescales are accessible using modern methods of ultrafast spectroscopy. Measurements of pseudorotation rates can lead to important information on the strength and nature of the JT coupling present. We will present analytical calculations that allow the rate of pseudorotation to be determined in terms of the vibronic coupling parameters. We will show how these results can be applied to E ⊗ e systems and then to the more complicated system applicable to C60- anions. This is of particular interest because of the high icosahedral symmetry of fullerene ions and also because of the many potential uses of materials containing these ions. We conclude by outlining experiments that should be capable of measuring pseudorotation in C 60 anions.

  18. Dynamic chemistry of anion recognition

    SciTech Connect

    Custelcean, Radu

    2012-01-01

    In the past 40 years, anion recognition by synthetic receptors has grown into a rich and vibrant research topic, developing into a distinct branch of Supramolecular Chemistry. Traditional anion receptors comprise organic scaffolds functionalized with complementary binding groups that are assembled by multistep organic synthesis. Recently, a new approach to anion receptors has emerged, in which the host is dynamically self-assembled in the presence of the anionic guest, via reversible bond formation between functional building units. While coordination bonds were initially employed for the self-assembly of the anion hosts, more recent studies demonstrated that reversible covalent bonds can serve the same purpose. In both cases, due to their labile connections, the molecular constituents have the ability to assemble, dissociate, and recombine continuously, thereby creating a dynamic combinatorial library (DCL) of receptors. The anionic guests, through specific molecular recognition, may then amplify (express) the formation of a particular structure among all possible combinations (real or virtual) by shifting the equilibria involved towards the most optimal receptor. This approach is not limited to solution self-assembly, but is equally applicable to crystallization, where the fittest anion-binding crystal may be selected. Finally, the pros and cons of employing dynamic combinatorial chemistry (DCC) vs molecular design for developing anion receptors, and the implications of both approaches to selective anion separations, will be discussed.

  19. A classical force field for tetrahedral oxyanions developed using hydration properties: The examples of pertechnetate (TcO4-) and sulfate (SO42-)

    NASA Astrophysics Data System (ADS)

    Williams, Christopher D.; Carbone, Paola

    2015-11-01

    Radioactive pertechnetate, 99TcO4-, is one of the most problematic ionic species in the context of the clean up and storage of nuclear waste. Molecular simulations can be used to understand the behavior of TcO4- in dilute aqueous solutions, providing reliable potentials are available. This work outlines the development of a new potential model for TcO 4- and competing SO42-, optimized using their hydration properties, such as the Gibbs hydration free energy (calculated using Bennett's acceptance ratio method). The findings show that the TcO4- oxyanion has a very low hydration free energy (-202 kJ mol-1) compared to other anions (Cl-, I-, SO42-) leading to fast water exchange dynamics and explaining its observed high mobility in the aqueous environment. Its hydrated structure, investigated using ion-water radial distribution functions, shows that it is unique amongst the other anions in that it does not possess well-defined hydration shells. Since contaminants and ubiquitous species in the aqueous environment are often present as tetrahedral oxyanions, it is proposed that the approach could easily be extended to a whole host of other species.

  20. A classical force field for tetrahedral oxyanions developed using hydration properties: The examples of pertechnetate (TcO4(-)) and sulfate (SO4(2-)).

    PubMed

    Williams, Christopher D; Carbone, Paola

    2015-11-07

    Radioactive pertechnetate, (99)TcO4(-), is one of the most problematic ionic species in the context of the clean up and storage of nuclear waste. Molecular simulations can be used to understand the behavior of TcO4(-) in dilute aqueous solutions, providing reliable potentials are available. This work outlines the development of a new potential model for TcO4(-) and competing SO4(2-), optimized using their hydration properties, such as the Gibbs hydration free energy (calculated using Bennett's acceptance ratio method). The findings show that the TcO4(-) oxyanion has a very low hydration free energy (-202 kJ mol(-1)) compared to other anions (Cl(-), I(-), SO4(2-)) leading to fast water exchange dynamics and explaining its observed high mobility in the aqueous environment. Its hydrated structure, investigated using ion-water radial distribution functions, shows that it is unique amongst the other anions in that it does not possess well-defined hydration shells. Since contaminants and ubiquitous species in the aqueous environment are often present as tetrahedral oxyanions, it is proposed that the approach could easily be extended to a whole host of other species.

  1. Making Polymeric Microspheres

    NASA Technical Reports Server (NTRS)

    Rhim, Won-Kyu; Hyson, Michael T.; Chung, Sang-Kun; Colvin, Michael S.; Chang, Manchium

    1989-01-01

    Combination of advanced techniques yields uniform particles for biomedical applications. Process combines ink-jet and irradiation/freeze-polymerization techniques to make polymeric microspheres of uniform size in diameters from 100 to 400 micrometer. Microspheres used in chromatography, cell sorting, cell labeling, and manufacture of pharmaceutical materials.

  2. Making Polymeric Microspheres

    NASA Technical Reports Server (NTRS)

    Rhim, Won-Kyu; Hyson, Michael T.; Chung, Sang-Kun; Colvin, Michael S.; Chang, Manchium

    1989-01-01

    Combination of advanced techniques yields uniform particles for biomedical applications. Process combines ink-jet and irradiation/freeze-polymerization techniques to make polymeric microspheres of uniform size in diameters from 100 to 400 micrometer. Microspheres used in chromatography, cell sorting, cell labeling, and manufacture of pharmaceutical materials.

  3. Step-Growth Polymerization.

    ERIC Educational Resources Information Center

    Stille, J. K.

    1981-01-01

    Following a comparison of chain-growth and step-growth polymerization, focuses on the latter process by describing requirements for high molecular weight, step-growth polymerization kinetics, synthesis and molecular weight distribution of some linear step-growth polymers, and three-dimensional network step-growth polymers. (JN)

  4. Anionic and zwitterionic copper(I) complexes incorporating an anionic N-heterocyclic carbene decorated with a malonate backbone: synthesis, structure and catalytic applications.

    PubMed

    César, Vincent; Barthes, Cécile; Farré, Yoann C; Cuisiat, Stéphane V; Vacher, Bernard Y; Brousses, Rémy; Lugan, Noël; Lavigne, Guy

    2013-05-28

    The anionic malonate-derived N-heterocyclic carbenes (maloNHCs) react cleanly and rapidly with copper chloride to generate the anionic complexes of type [(maloNHC)CuCl]·Li, which crystallize in the solid state either in an oligomeric trimer arrangement or in polymeric helixes depending on the substitution pattern and the solvent. Ten zwitterionic heteroleptic Cu(I) complexes combining the anionic maloNHC and a neutral imidazol-2-ylidene are also obtained in a very selective manner and fully characterized. Whereas the anionic complexes are relatively active catalysts for the hydrosilylation of carbonyl compounds, the zwitterionic complexes reveal to be efficient and extremely robust pre-catalysts for the intramolecular cyclopropanation reaction of a diazo ester and outperform the corresponding cationic Cu(i) complexes with classical imidazol-2-ylidenes.

  5. Polymeric Carbon Dioxide

    SciTech Connect

    Yoo, C-S.

    1999-11-02

    Synthesis of polymeric carbon dioxide has long been of interest to many chemists and materials scientists. Very recently we discovered the polymeric phase of carbon dioxide (called CO{sub 2}-V) at high pressures and temperatures. Our optical and x-ray results indicate that CO{sub 2}-V is optically non-linear, generating the second harmonic of Nd: YLF laser at 527 nm and is also likely superhard similar to cubic-boron nitride or diamond. CO{sub 2}-V is made of CO{sub 4} tetrahedra, analogous to SiO{sub 2} polymorphs, and is quenchable at ambient temperature at pressures above 1 GPa. In this paper, we describe the pressure-induced polymerization of carbon dioxide together with the stability, structure, and mechanical and optical properties of polymeric CO{sub 2}-V. We also present some implications of polymeric CO{sub 2} for high-pressure chemistry and new materials synthesis.

  6. A review of defects and disorder in multinary tetrahedrally bonded semiconductors

    NASA Astrophysics Data System (ADS)

    Baranowski, Lauryn L.; Zawadzki, Pawel; Lany, Stephan; Toberer, Eric S.; Zakutayev, Andriy

    2016-12-01

    Defects are critical to understanding the electronic properties of semiconducting compounds, for applications such as light-emitting diodes, transistors, photovoltaics, and thermoelectrics. In this review, we describe our work investigating defects in tetrahedrally bonded, multinary semiconductors, and discuss the place of our research within the context of publications by other groups. We applied experimental and theory techniques to understand point defects, structural disorder, and extended antisite defects in one semiconductor of interest for photovoltaic applications, Cu2SnS3. We contrast our findings on Cu2SnS3 with other chemically related Cu-Sn-S compounds, as well as structurally related compounds such as Cu2ZnSnS4 and Cu(In,Ga)Se2. We find that evaluation of point defects alone is not sufficient to understand defect behavior in multinary tetrahedrally bonded semiconductors. In the case of Cu2SnS3 and Cu2ZnSnS4, structural disorder and entropy-driven cation clustering can result in nanoscale compositional inhomogeneities which detrimentally impact the electronic transport. Therefore, it is not sufficient to assess only the point defect behavior of new multinary tetrahedrally bonded compounds; effects such as structural disorder and extended antisite defects must also be considered. Overall, this review provides a framework for evaluating tetrahedrally bonded semiconducting compounds with respect to their defect behavior for photovoltaic and other applications, and suggests new materials that may not be as prone to such imperfections.

  7. Fostering Teacher Development to a Tetrahedral Orientation in the Teaching of Chemistry

    ERIC Educational Resources Information Center

    Lewthwaite, Brian; Wiebe, Rick

    2011-01-01

    This paper reports on the initial outcomes from the end of the fourth year of a 5 year research and professional development project to improve chemistry teaching among three cohorts of chemistry teachers in Manitoba, Canada. The project responds to a new curriculum introduction advocating a tetrahedral orientation (Mahaffy, "Journal of…

  8. Automated Tetrahedral Mesh Generation for CFD Analysis of Aircraft in Conceptual Design

    NASA Technical Reports Server (NTRS)

    Ordaz, Irian; Li, Wu; Campbell, Richard L.

    2014-01-01

    The paper introduces an automation process of generating a tetrahedral mesh for computational fluid dynamics (CFD) analysis of aircraft configurations in early conceptual design. The method was developed for CFD-based sonic boom analysis of supersonic configurations, but can be applied to aerodynamic analysis of aircraft configurations in any flight regime.

  9. Multi-Dimensional, Inviscid Flux Reconstruction for Simulation of Hypersonic Heating on Tetrahedral Grids

    NASA Technical Reports Server (NTRS)

    Gnoffo, Peter A.

    2009-01-01

    The quality of simulated hypersonic stagnation region heating on tetrahedral meshes is investigated by using a three-dimensional, upwind reconstruction algorithm for the inviscid flux vector. Two test problems are investigated: hypersonic flow over a three-dimensional cylinder with special attention to the uniformity of the solution in the spanwise direction and hypersonic flow over a three-dimensional sphere. The tetrahedral cells used in the simulation are derived from a structured grid where cell faces are bisected across the diagonal resulting in a consistent pattern of diagonals running in a biased direction across the otherwise symmetric domain. This grid is known to accentuate problems in both shock capturing and stagnation region heating encountered with conventional, quasi-one-dimensional inviscid flux reconstruction algorithms. Therefore the test problem provides a sensitive test for algorithmic effects on heating. This investigation is believed to be unique in its focus on three-dimensional, rotated upwind schemes for the simulation of hypersonic heating on tetrahedral grids. This study attempts to fill the void left by the inability of conventional (quasi-one-dimensional) approaches to accurately simulate heating in a tetrahedral grid system. Results show significant improvement in spanwise uniformity of heating with some penalty of ringing at the captured shock. Issues with accuracy near the peak shear location are identified and require further study.

  10. DNA tetrahedral scaffolds-based platform for the construction of electrochemiluminescence biosensor.

    PubMed

    Feng, Qiu-Mei; Zhou, Zhen; Li, Mei-Xing; Zhao, Wei; Xu, Jing-Juan; Chen, Hong-Yuan

    2017-04-15

    Proximal metallic nanoparticles (NPs) could quench the electrochemiluminescence (ECL) emission of semiconductor quantum dots (QDs) due to Förster energy transfer (FRET), but at a certain distance, the coupling of light-emission with surface plasmon resonance (SPR) result in enhanced ECL. Thus, the modification strategies and distances control between QDs and metallic NPs are critical for the ECL intensity of QDs. In this strategy, a SPR enhanced ECL sensor based on DNA tetrahedral scaffolds modified platform was reported for the detection of telomerase activity. Due to the rigid three-dimensional structure, DNA tetrahedral scaffolds grafting on the electrode surface could accurately modulate the distance between CdS QDs and luminol labelled gold nanoparticles (L-Au NPs), meanwhile provide an enhanced spatial dimension and accessibility for the assembly of multiple L-Au NPs. The ECL intensities of both CdS QDs (-1.25V vs. SCE) and luminol (+0.33V vs. SCE) gradually increased along with the formation of multiple L-Au NPs at the vertex of DNA tetrahedral scaffolds induced by telomerase, bringing in a dual-potential ECL analysis. The proposed method showed high sensitivity for the identification of telomerase and was successfully applied for the differentiation of cancer cells from normal cells. This work suggests that DNA tetrahedral scaffolds could serve as an excellent choice for the construction of SPR-ECL system.

  11. Mixed-metal chalcogenide tetrahedral clusters with an exo-polyhedral metal fragment.

    PubMed

    Yuvaraj, K; Roy, Dipak Kumar; Anju, V P; Mondal, Bijnaneswar; Varghese, Babu; Ghosh, Sundargopal

    2014-12-07

    The reaction of metal carbonyl compounds with group 6 and 8 metallaboranes led us to report the synthesis and structural characterization of several novel mixed-metal chalcogenide tetrahedral clusters. Thermolysis of arachno-[(Cp*RuCO)2B2H6], 1, and [Os3(CO)12] in the presence of 2-methylthiophene yielded [Cp*Ru(CO)2(μ-H){Os3(CO)9}S], 3, and [Cp*Ru(μ-H){Os3(CO)11}], 4. In a similar fashion, the reaction of [(Cp*Mo)2B5H9], 2, with [Ru3(CO)12] and 2-methylthiophene yielded [Cp*Ru(CO)2(μ-H){Ru3(CO)9}S], 5, and conjuncto-[(Cp*Mo)2B5H8(μ-H){Ru3(CO)9}S], 6. Both compounds 3 and 5 can be described as 50-cve (cluster valence electron) mixed-metal chalcogenide clusters, in which a sulfur atom replaces one of the vertices of the tetrahedral core. Compounds 3 and 5 possess a [M3S] tetrahedral core, in which the sulfur is attached to an exo-metal fragment, unique in the [M3S] metal chalcogenide tetrahedral arrangements. All the compounds have been characterized by mass spectrometry, IR, and (1)H, (11)B and (13)C NMR spectroscopy in solution, and the solid state structures were unequivocally established by crystallographic analysis of compounds 3, 5 and 6.

  12. Fostering Teacher Development to a Tetrahedral Orientation in the Teaching of Chemistry

    ERIC Educational Resources Information Center

    Lewthwaite, Brian; Wiebe, Rick

    2011-01-01

    This paper reports on the initial outcomes from the end of the fourth year of a 5 year research and professional development project to improve chemistry teaching among three cohorts of chemistry teachers in Manitoba, Canada. The project responds to a new curriculum introduction advocating a tetrahedral orientation (Mahaffy, "Journal of…

  13. A New Species of Streptocephalus Fairy Shrimp (Crustacea, Anostraca) with Tetrahedral Cysts from Central Thailand

    NASA Astrophysics Data System (ADS)

    Sanoamuang, La-Orsri; Saengphan, Nukul

    2006-06-01

    A new species of fairy shrimp, Streptocephalus siamensis n. sp., is described from five temporary pools in Suphan Buri and Kanchana Buri Provinces, central Thailand. It sometimes co-occurs with its congener, S. sirindhornae . This new species belongs to the subgenus Parastreptocephalus which is defined by bearing tetrahedral cysts. This is the third anostracan species reported from Thailand.

  14. Anion permselective membrane

    NASA Technical Reports Server (NTRS)

    Alexander, S.; Hodgdon, R. B.

    1977-01-01

    The objective of NAS 3-20108 was the development and evaluation of improved anion selective membranes useful as efficient separators in a redox power storage cell system being constructed. The program was divided into three parts, (a) optimization of the selected candidate membrane systems, (b) investigation of alternative membrane/polymer systems, and (c) characterization of candidate membranes. The major synthesis effort was aimed at improving and optimizing as far as possible each candidate system with respect to three critical membrane properties essential for good redox cell performance. Substantial improvements were made in 5 candidate membrane systems. The critical synthesis variables of cross-link density, monomer ratio, and solvent composition were examined over a wide range. In addition, eight alternative polymer systems were investigated, two of which attained candidate status. Three other alternatives showed potential but required further research and development. Each candidate system was optimized for selectivity.

  15. Organic Anion Transporting Polypeptides

    PubMed Central

    Stieger, Bruno; Hagenbuch, Bruno

    2013-01-01

    Organic anion transporting polypeptides or OATPs are central transporters in the disposition of drugs and other xenobiotics. In addition, they mediate transport of a wide variety of endogenous substrates. The critical role of OATPs in drug disposition has spurred research both in academia and in the pharmaceutical industry. Translational aspects with clinical questions are the focus in academia, while the pharmaceutical industry tries to define and understand the role these transporters play in pharmacotherapy. The present overview summarizes our knowledge on the interaction of food constituents with OATPs, and on the OATP transport mechanisms. Further, it gives an update on the available information on the structure-function relationship of the OATPs, and finally, covers the transcriptional and posttranscriptional regulation of OATPs. PMID:24745984

  16. Anion transport and supramolecular medicinal chemistry.

    PubMed

    Gale, Philip A; Davis, Jeffery T; Quesada, Roberto

    2017-04-05

    New approaches to the transmembrane transport of anions are discussed in this review. Advances in the design of small molecule anion carriers are reviewed in addition to advances in the design of synthetic anion channels. The application of anion transporters to the potential future treatment of disease is discussed in the context of recent findings on the selectivity of anion transporters.

  17. Resonant spectra of quadrupolar anions

    NASA Astrophysics Data System (ADS)

    Fossez, K.; Mao, Xingze; Nazarewicz, W.; Michel, N.; Garrett, W. R.; Płoszajczak, M.

    2016-09-01

    In quadrupole-bound anions, an extra electron is attached at a sufficiently large quadrupole moment of a neutral molecule, which is lacking a permanent dipole moment. The nature of the bound states and low-lying resonances of such anions is of interest for understanding the threshold behavior of open quantum systems in general. In this work, we investigate the properties of quadrupolar anions as halo systems, the formation of rotational bands, and the transition from a subcritical to supercritical electric quadrupole moment. We solve the electron-plus-rotor problem using a nonadiabatic coupled-channel formalism by employing the Berggren ensemble, which explicitly contains bound states, narrow resonances, and the scattering continuum. The rotor is treated as a linear triad of point charges with zero monopole and dipole moments and nonzero quadrupole moment. We demonstrate that binding energies and radii of quadrupolar anions strictly follow the scaling laws for two-body halo systems. Contrary to the case of dipolar anions, ground-state band of quadrupolar anions smoothly extend into the continuum, and many rotational bands could be identified above the detachment threshold. We study the evolution of a bound state of an anion as it dives into the continuum at a critical quadrupole moment and we show that the associated critical exponent is α =2 . Everything considered, quadrupolar anions represent a perfect laboratory for the studies of marginally bound open quantum systems.

  18. Finite Element Simulation of Articular Contact Mechanics with Quadratic Tetrahedral Elements

    PubMed Central

    Maas, Steve A.; Ellis, Benjamin J.; Rawlins, David S.; Weiss, Jeffrey A.

    2016-01-01

    Although it is easier to generate finite element discretizations with tetrahedral elements, trilinear hexahedral (HEX8) elements are more often used in simulations of articular contact mechanics. This is due to numerical shortcomings of linear tetrahedral (TET4) elements, limited availability of quadratic tetrahedron elements in combination with effective contact algorithms, and the perceived increased computational expense of quadratic finite elements. In this study we implemented both ten-node (TET10) and fifteen-node (TET15) quadratic tetrahedral elements in FEBio (www.febio.org) and compared their accuracy, robustness in terms of convergence behavior and computational cost for simulations relevant to articular contact mechanics. Suitable volume integration and surface integration rules were determined by comparing the results of several benchmark contact problems. The results demonstrated that the surface integration rule used to evaluate the contact integrals for quadratic elements affected both convergence behavior and accuracy of predicted stresses. The computational expense and robustness of both quadratic tetrahedral formulations compared favorably to the HEX8 models. Of note, the TET15 element demonstrated superior convergence behavior and lower computational cost than both the TET10 and HEX8 elements for meshes with similar numbers of degrees of freedom in the contact problems that we examined. Finally, the excellent accuracy and relative efficiency of these quadratic tetrahedral elements was illustrated by comparing their predictions with those for a HEX8 mesh for simulation of articular contact in a fully validated model of the hip. These results demonstrate that TET10 and TET15 elements provide viable alternatives to HEX8 elements for simulation of articular contact mechanics. PMID:26900037

  19. A tetrahedral mesh generation approach for 3D marine controlled-source electromagnetic modeling

    NASA Astrophysics Data System (ADS)

    Um, Evan Schankee; Kim, Seung-Sep; Fu, Haohuan

    2017-03-01

    3D finite-element (FE) mesh generation is a major hurdle for marine controlled-source electromagnetic (CSEM) modeling. In this paper, we present a FE discretization operator (FEDO) that automatically converts a 3D finite-difference (FD) model into reliable and efficient tetrahedral FE meshes for CSEM modeling. FEDO sets up wireframes of a background seabed model that precisely honors the seafloor topography. The wireframes are then partitioned into multiple regions. Outer regions of the wireframes are discretized with coarse tetrahedral elements whose maximum size is as large as a skin depth of the regions. We demonstrate that such coarse meshes can produce accurate FE solutions because numerical dispersion errors of tetrahedral meshes do not accumulate but oscillates. In contrast, central regions of the wireframes are discretized with fine tetrahedral elements to describe complex geology in detail. The conductivity distribution is mapped from FD to FE meshes in a volume-averaged sense. To avoid excessive mesh refinement around receivers, we introduce an effective receiver size. Major advantages of FEDO are summarized as follow. First, FEDO automatically generates reliable and economic tetrahedral FE meshes without adaptive meshing or interactive CAD workflows. Second, FEDO produces FE meshes that precisely honor the boundaries of the seafloor topography. Third, FEDO derives multiple sets of FE meshes from a given FD model. Each FE mesh is optimized for a different set of sources and receivers and is fed to a subgroup of processors on a parallel computer. This divide and conquer approach improves the parallel scalability of the FE solution. Both accuracy and effectiveness of FEDO are demonstrated with various CSEM examples.

  20. Finite element simulation of articular contact mechanics with quadratic tetrahedral elements.

    PubMed

    Maas, Steve A; Ellis, Benjamin J; Rawlins, David S; Weiss, Jeffrey A

    2016-03-21

    Although it is easier to generate finite element discretizations with tetrahedral elements, trilinear hexahedral (HEX8) elements are more often used in simulations of articular contact mechanics. This is due to numerical shortcomings of linear tetrahedral (TET4) elements, limited availability of quadratic tetrahedron elements in combination with effective contact algorithms, and the perceived increased computational expense of quadratic finite elements. In this study we implemented both ten-node (TET10) and fifteen-node (TET15) quadratic tetrahedral elements in FEBio (www.febio.org) and compared their accuracy, robustness in terms of convergence behavior and computational cost for simulations relevant to articular contact mechanics. Suitable volume integration and surface integration rules were determined by comparing the results of several benchmark contact problems. The results demonstrated that the surface integration rule used to evaluate the contact integrals for quadratic elements affected both convergence behavior and accuracy of predicted stresses. The computational expense and robustness of both quadratic tetrahedral formulations compared favorably to the HEX8 models. Of note, the TET15 element demonstrated superior convergence behavior and lower computational cost than both the TET10 and HEX8 elements for meshes with similar numbers of degrees of freedom in the contact problems that we examined. Finally, the excellent accuracy and relative efficiency of these quadratic tetrahedral elements was illustrated by comparing their predictions with those for a HEX8 mesh for simulation of articular contact in a fully validated model of the hip. These results demonstrate that TET10 and TET15 elements provide viable alternatives to HEX8 elements for simulation of articular contact mechanics. Copyright © 2016 Elsevier Ltd. All rights reserved.

  1. Accumulation of Tetrahedral Intermediates in Cholinesterase Catalysis: A Secondary Isotope Effect Study

    PubMed Central

    Tormos, Jose R.; Wiley, Kenneth L.; Wang, Yi; Fournier, Didier; Masson, Patrick; Nachon, Florian; Quinn, Daniel M.

    2010-01-01

    In a previous communication, kinetic β-deuterium secondary isotope effects were reported that support a mechanism for substrate-activated turnover of acetylthiocholine by human butyrylcholinesterase (BuChE) wherein the accumulating reactant state is a tetrahedral intermediate (Tormos, J. R., et al. (2005) JACS 127, 14538–14539). In this paper additional isotope effect experiments are described with acetyl-labeled acetylthiocholines (CL3COSCH2CH2N+Me3; L = H or D) that also support accumulation of the tetrahedral intermediate in Drosophila melanogaster acetylcholinesterase (DmAChE) catalysis. In contrast to the aforementioned BuChE-catalyzed reaction, for this reaction the dependence of initial rates on substrate concentration is marked by pronounced substrate inhibition at high substrate concentrations. Moreover, kinetic β -deuterium secondary isotope effects for turnover of acetylthiocholine depended on substrate concentration, and gave the following: D3kcat/Km = 0.95 ± 0.03, D3kcat = 1.12 ± 0.02 and D3 β kcat = 0.97 ± 0.04. The inverse isotope effect on kcat/Km is consistent with conversion of the sp2 hybridized substrate carbonyl in the E + A reactant state into a quasi-tetrahedral transition state in the acylation stage of catalysis, whereas the markedly normal isotope effect on kcat is consistent with hybridization change from sp3 toward sp2 as the reactant state for deacylation is converted into the subsequent transition state. Transition states for Drosophila melanogaster AChE-catalyzed hydrolysis of acetylthiocholine were further characterized by measuring solvent isotope effects and determining proton inventories. These experiments indicated that the transition state for rate-determining decomposition of the tetrahedral intermediate is stabilized by multiple protonic interactions. Finally, a simple model is proposed for the contribution that tetrahedral intermediate stabilization provides to the catalytic power of acetylcholinesterase. PMID

  2. Updates to Multi-Dimensional Flux Reconstruction for Hypersonic Simulations on Tetrahedral Grids

    NASA Technical Reports Server (NTRS)

    Gnoffo, Peter A.

    2010-01-01

    The quality of simulated hypersonic stagnation region heating with tetrahedral meshes is investigated by using an updated three-dimensional, upwind reconstruction algorithm for the inviscid flux vector. An earlier implementation of this algorithm provided improved symmetry characteristics on tetrahedral grids compared to conventional reconstruction methods. The original formulation however displayed quantitative differences in heating and shear that were as large as 25% compared to a benchmark, structured-grid solution. The primary cause of this discrepancy is found to be an inherent inconsistency in the formulation of the flux limiter. The inconsistency is removed by employing a Green-Gauss formulation of primitive gradients at nodes to replace the previous Gram-Schmidt algorithm. Current results are now in good agreement with benchmark solutions for two challenge problems: (1) hypersonic flow over a three-dimensional cylindrical section with special attention to the uniformity of the solution in the spanwise direction and (2) hypersonic flow over a three-dimensional sphere. The tetrahedral cells used in the simulation are derived from a structured grid where cell faces are bisected across the diagonal resulting in a consistent pattern of diagonals running in a biased direction across the otherwise symmetric domain. This grid is known to accentuate problems in both shock capturing and stagnation region heating encountered with conventional, quasi-one-dimensional inviscid flux reconstruction algorithms. Therefore the test problems provide a sensitive indicator for algorithmic effects on heating. Additional simulations on a sharp, double cone and the shuttle orbiter are then presented to demonstrate the capabilities of the new algorithm on more geometrically complex flows with tetrahedral grids. These results provide the first indication that pure tetrahedral elements utilizing the updated, three-dimensional, upwind reconstruction algorithm may be used for the

  3. Bound Anionic States of Aadenine

    SciTech Connect

    Haranczyk, Maciej; Gutowski, Maciej S.; Li, Xiang; Bowen, Kit H.

    2007-03-20

    The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. Anionic states of nucleic acid bases are involved in DNA damage by low-energy electrons and in charge transfer through DNA. Previous gas phase studies of free, unsolvated nucleic acid base parent anions probed only dipole-bound states, which are not present in condensed phase environments, but did not observe valence anionic states, which for purine bases are thought to be adiabatically unbound. Contrary to this expectation,wehave demonstrated that some thus far ignored tautomers of adenine, which result from enamine-imine transformations, support valence anionic states with electron vertical detachment energies as large as 2.2 eV, and at least one of these anionic tautomers is adiabatically bound. Moreover, we predict that the new anionic tautomers should also dominate in solutions and should be characterized by larger values of electron vertical detachment energy than the canonical valence anion. All of the newfound anionic tautomers might be formed in the course of dissociative electron attachment followed by a hydrogen atom attachment to a carbon atom, and they might affect the structure and properties of DNA and RNA exposed to low-energy electrons. The new valence states observed here, unlike the dipole-bound state, could exist in condensed phases and might be relevant to radiobiological damage. The discovery of these valence anionic states of adenine was facilitated by the development of (i) an experimental method for preparing parent anions of nucleic acid bases for photoelectron experiments, and (ii) a combinatorial/quantum chemical approach for identification of the most stable tautomers of organic molecules.

  4. Bound Anionic States of Adenine

    SciTech Connect

    Haranczyk, Maciej; Gutowski, Maciej S.; Li, Xiang; Bowen, Kit H.

    2007-03-20

    The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. Anionic states of nucleic acid bases are involved in DNA damage by low-energy electrons and in charge transfer through DNA. Previous gas phase studies of free, unsolvated nucleic acid base parent anions probed only dipole-bound states, which are not present in condensed phase environments, but did not observe valence anionic states, which for purine bases are thought to be adiabatically unbound. Contrary to this expectation, we have demonstrated that some thus far ignored tautomers of adenine, which result from enamine-imine transformations, support valence anionic states with electron vertical detachment energies as large as 2.2 eV, and at least one of these anionic tautomers is adiabatically bound. Moreover, we predict that the new anionic tautomers should also dominate in solutions and should be characterized by larger values of electron vertical detachment energy than the canonical valence anion. All of the newfound anionic tautomers might be formed in the course of dissociative electron attachment followed by a hydrogen atom attachment to a carbon atom, and they might affect the structure and properties of DNA and RNA exposed to low-energy electrons. The new valence states observed here, unlike the dipole-bound state, could exist in condensed phases and might be relevant to radiobiological damage. The discovery of these valence anionic states of adenine was facilitated by the development of (i) an experimental method for preparing parent anions of nucleic acid bases for photoelectron experiments, and (it) a combinatorial/quantum chemical approach for identification of the most stable tautomers of organic molecules.

  5. Palladium (II) catalyized polymerization of norbornene and acrylates

    DOEpatents

    Sen, Ayusman; Kacker, Smita; Hennis, April; Polley, Jennifer D.

    2000-08-29

    Homopolymers or copolymers of acrylates, homopolymers or copolymers of norbornenes, and copolymers of acrylates with norbornenes, may be prepared by contacting acrylate and/or norbornene monomer reactant under polymerization conditions and in the presence of a solvent with a catalyst system consisting essentially of a Pd(II) dimer component having the formula: [(L)Pd(R)(X)].sub.2, where L is a monodentate phosphorus or nitrogen ligand, X is an anionic group, and R is an alkyl or aryl group.

  6. Palladium (Ii) Catalyzed Polymerization Of Norbornene And Acrylates

    DOEpatents

    Sen, Ayusman; Kacker, Smita; Hennis, April; Polley, Jennifer D.

    2001-10-09

    Homopolymers or copolymers of acrylates, homopolymers or copolymers of norbornenes, and copolymers of acrylates with norbornenes, may be prepared by contacting acrylate and/or norbornene monomer reactant under polymerization conditions and in the presence of a solvent with a catalyst system consisting essentially of a Pd(II) dimer component having the formula: where L is a monodentate phosphorus or nitrogen ligand, X is an anionic group, and R is an alkyl or aryl group.

  7. A new anion-exchange/hydrophobic monolith as stationary phase for nano liquid chromatography of small organic molecules and inorganic anions.

    PubMed

    Aydoğan, Cemil

    2015-05-01

    In this study, an anion-exchange/hydrophobic polymethacrylate-based stationary phase was prepared for nano-liquid chromatography of small organic molecules and inorganic anions. The stationary phase was synthesized by in situ polymerization of 3-chloro-2-hydroxypropylmethacrylate and ethylene dimethacrylate inside silanized 100 μm i.d. fused silica capillary. The porogen mixture consisted of toluene and dodecanol. The pore size distrubution profiles of the resulting monolith were determined by mercury intrusion porosimetry and the morphology of the prepared monolith was investigated by scanning electron microscope. Good permeability, stability and column efficiency were observed on the monolithic column with nano flow. The produced monolithic column, which contains reactive chloro groups, was then modified by reaction with N,N-dimethyl-N-dodecylamine to obtain an anion-exchange/hydrophobic monolithic stationary phase. The functionalized monolith contained ionizable amine groups and hydrophobic groups that are useful of anion-exchange/hydrophobic mixed-mode chromatography. The final monolithic column performance with respect to anion-exchange and hydrophobic interactions was assesed by the separation of alkylbenzene derivatives, phenolic compounds and inorganic anions, respectively. Theoretical plate numbers up to 23,000 plates/m were successfully achieved in the separation of inorganic anions.

  8. Structure and selectivity trends in crystalline urea-functionalized anion-binding capsules

    SciTech Connect

    Rajbanshi, Arbin; Custelcean, Radu

    2012-01-01

    A tripodal trisurea receptor (L1) persistently self-assembles with various divalent oxoanion salts M{sub n}X (M = Na, K, Mg, Ca, Cd; X = SO{sub 4}{sup 2-}, SO{sub 3}{sup 2-}, SeO{sub 4}{sup 2-}, CrO{sub 4}{sup 2-}) into isomorphous series of crystalline frameworks in three different compositions: MX(L1){sub 2}(H{sub 2}O){sub 6} (M = Mg, Ca, Cd) (1), Na{sub 2}X(L1){sub 2}(H{sub 2}O){sub 4} (2) and K{sub 2}X(L1){sub 2}(H{sub 2}O){sub 2} (3). Single-crystal X-ray structural analysis revealed that all three series of structures adopt a NaCl-type topology, consisting of alternating anionic X(L1){sub 2}{sup 2-} capsules and M(H{sub 2}O){sub 6}{sup 2+}, Na{sub 2}(H{sub 2}O){sub 4}{sup 2+} or K{sub 2}(H{sub 2}O){sub 2}{sup 2+} hydrated cations. The capsules provide a complementary environment to tetrahedral oxoanions via 12 hydrogen bonds from six urea groups lining the cavities of the capsules. The persistent formation of the capsules facilitated the investigation of structural trends and structure-selectivity relationships across series 1-3. First, it was found that the size of the capsules is relatively unresponsive to the change in the encapsulated anion, resulting in good shape and size recognition in the separation of anions by competitive crystallizations. Second, it was found that the size of the capsules varies linearly with the size of the external cation, which provides a way for tuning the anion encapsulation selectivity. However, no straightforward dependence was found between the size of the capsules and the relative selectivity for different-sized tetrahedral oxoanions in competitive crystallizations.

  9. High-capacity anion exchangers based on poly (glycidylmethacrylate-divinylbenzene) microspheres for ion chromatography.

    PubMed

    Liu, Junwei; Wang, Yong; Cheng, Heli; Wang, Nani; Wu, Shuchao; Zhang, Peimin; Zhu, Yan

    2016-10-01

    Poly (glycidylmethacrylate-divinylbenzene) microspheres were prepared by the two-staged swelling and polymerization method and applied to prepare anion exchange stationary phases. Methylamine, dimethylamine, trimethylamine, diethylamine and triethylamine were selected to prepare the quaternary ammonium groups of anion exchangers, respectively. The diameters and surface characteristics of microspheres were measured by scanning electron microscope and nitrogen adsorption-desorption measurements. The anion exchangers were characterized by Fourier transform infrared spectrum, elemental analysis and breakthrough curve methods. The chromatographic performances of anion exchangers were illustrated by separating conventional anions, organic weak acids and carbohydrates. The results indicated that the anion exchange capacities were controllable by changing either the content of glycidylmethacrylate in microspheres or the number of bonded quaternary ammonium layer. Meanwhile, the substituents of quaternary ammonium groups greatly influenced the separation properties of anion exchangers. Finally, the three-layer methylamine-quaternized anion exchanger was successfully applied for the determination of fluoride in tea sample. The content of fluoride was detected to be 0.13mgg(-1) without the interference of acetate and formate.

  10. Anion-exchange nanospheres as titration reagents for anionic analytes.

    PubMed

    Zhai, Jingying; Xie, Xiaojiang; Bakker, Eric

    2015-08-18

    We present here anion-exchange nanospheres as novel titration reagents for anions. The nanospheres contain a lipophilic cation for which the counterion is initially Cl(-). Ion exchange takes place between Cl(-) in the nanospheres and a more lipophilic anion in the sample, such as ClO4(-) and NO3(-). Consecutive titration in the same sample solution for ClO4(-) and NO3(-) were demonstrated. As an application, the concentration of NO3(-) in spinach was successfully determined using this method.

  11. Waterborne Polymeric Films.

    DTIC Science & Technology

    1981-02-01

    Parameters of Test Fluids I " 3. Energies of Vaporization and Molar Volumes of Some Acrylic Monomers 29 4. Physical Properties of Synthetic Polymers 31 S...Physical Properties of Synthetic Acrylic Aqueous Dispersions 33 6. Anionic Acrylic Clear-film Formulations 35 7 Fluid Resistance of Anionic Acrylic...41 11. Energeis of Vaporization and Molar Volumes of Some Polyurethanes 45 12. Solution Properties of Synthetic Polyurethanes 47 13. Aqueous

  12. Anion selectivity in biological systems.

    PubMed

    Wright, E M; Diamond, J M

    1977-01-01

    As background for appreciating the still-unsolved problems of monovalent anion selectivity, we summarize the facts and intepretations that seem reasonably well established. In section II we saw that specific effects of monovalent anions on biological and physical systems define qualitative patterns, in that only certain sequences of anion effects are observed. For example, the 4 halides can be permitted on paper as 4! = 24 sequences, yet only 5 of these sequences have been observed in nature as potency sequences. In addition, there are quantitative regularities in anion potency that permit the construction of so-called empirical selectivity isotherms (Figs. 4 and 13). That is, a given potency sequence is found to be associated with only a certain modest range of selectivity ratios. The sequences and isotherms apply to effects with a nonequilibrium component (e.g., permeability and conductance sequences) as well as to purely equilibrium effects. Since students of cation selectivity have had difficulty accepting this conclusion, we discuss the reasons why it is not as paradoxical as it at first seems. In sections III and IV we develop four theoretical models to account for the observed anion potency sequences as sequences of equilibrium binding energies. Two of these models involve calculation of electrostatic binding energies between anions and monopolar or dipolar cationic sites, assuming anions as well as sites to be rigid and nonpolarizable. The other two models use thermochemically measured binding energies between anions and thealkali cations or occasionally alkaline-earth cations, which in fact approximate rigid, nonpolarizable spheres. All four models consider the anion selectivity pattern of a given cationic site to be determined by anion differences in the balance between hydration energies and ion-site binding energies. Site differences in anion selectivity pattern are attributed to site differences in radius, charge, coordination number, or dipole length

  13. Synthesis and Polymerization of Azaethylenes and Aza-1,3-dienes

    DTIC Science & Technology

    1993-04-08

    TERMS polymerization imine azadiene IT. SECURITY CLASSIFICATION EM RIRCRT CL SECURITY CLASS»ICATION at um Raw J£ SECURITY CLASSIFICATION m Miisat...program on the synthesis and polymerization of suitably substituted imines and azadienes under USARO sponsorship. We have shown that proper choice of... azadienes could be purified. NHoCN TiCt4 EtaN R = H, Me Neither azadiene would homopolymerize under either free radical or anionic conditions. With

  14. Anion transport with halogen bonds.

    PubMed

    Jentzsch, Andreas Vargas; Matile, Stefan

    2015-01-01

    This review covers the application of halogen bonds to transport anions across lipid bilayer membranes. The introduction provides a brief description of biological and synthetic transport systems. Emphasis is on examples that explore interactions beyond the coordination with lone pairs or hydrogen bonds for the recognition of cations and anions, particularly cation-π and anion-π interactions, and on structural motifs that are relevant for transport studies with halogen bonds. Section 2 summarizes the use of macrocyclic scaffolds to achieve transport with halogen bonds, focusing on cyclic arrays of halogen-bond donors of different strengths on top of calixarene scaffolds. This section also introduces methods to study anion binding in solution and anion transport in fluorogenic vesicles. In Sect. 3, transport studies with monomeric halogen bond-donors are summarized. This includes the smallest possible organic anion transporter, trifluoroiodomethane, a gas that can be bubbled through a suspension of vesicles to turn on transport. Anion transport with a gas nicely illustrates the power of halogen bonds for anion transport. Like hydrogen bonds, they are directional and strong, but compared to hydrogen-bond donors, halogen-bond donors are more lipophilic. Section 3 also offers a concise introduction to the measurement of ion selectivity in fluorogenic vesicles and conductance experiments in planar bilayer membranes. Section 4 introduces the formal unrolling of cyclic scaffolds into linear scaffolds that can span lipid bilayers. As privileged transmembrane scaffolds, the importance of hydrophobically matching fluorescent p-oligophenyl rods is fully confirmed. The first formal synthetic ion channel that operates by cooperative multiion hopping along transmembrane halogen-bonding cascades is described. Compared to homologs for anion-π interactions, transport with halogen bonds is clearly more powerful.

  15. Polymerization of 1,3-Dienes with Functional Groups. 4.

    NASA Astrophysics Data System (ADS)

    Takenaka, Katsuhiko; Shibata, Natsuyo; Tsuchida, Shinsuke; Takeshita, Hiroki; Miya, Masamitsu; Shiomi, Tomoo

    Anionic polymerization of N,N-diethyl-2-methylene-3-butenamide (DEA), which is a 1,3-butadiene derivative containing a diethylamide function, was carried out in tetrahydrofurane (THF) under various conditions. When DEA was polymerized in THF at -78°C using potassium naphthalenide (K-Naph) or diphenylmethylpotassium (DPMK) as an initiator, a polymer of predictable molecular weight with a narrow molecular weight distribution was obtained. However, the rate of polymerization was extremely slow to reach 80% conversion after 720 h. When the polymerization temperature was raised to 20°C, a low molecular weight oligomer with a broad molecular weight distribution was obtained because of a chain transfer reaction. On the other hand, no such side reaction occurred even at 20°C, when polymerization was carried out in the presence of LiCl. Also, the chain transfer reaction did not occur in lithium naphthalenide (Li-Naph) initiated polymerization. The microstructure of the polymer prepared using a potassium counter cation was a 1 : 1 mixture of 1,4-E and 1,2- structures. In the case of Li-Naph or DPMK/LiCl systems, the microstructure was a complicated mixture of 1,4-E, 1,4-Z, and 1,2-structures.

  16. Radical-Mediated Enzymatic Polymerizations

    PubMed Central

    Zavada, Scott R.; Battsengel, Tsatsral; Scott, Timothy F.

    2016-01-01

    Polymerization reactions are commonly effected by exposing monomer formulations to some initiation stimulus such as elevated temperature, light, or a chemical reactant. Increasingly, these polymerization reactions are mediated by enzymes―catalytic proteins―owing to their reaction efficiency under mild conditions as well as their environmental friendliness. The utilization of enzymes, particularly oxidases and peroxidases, for generating radicals via reduction-oxidation mechanisms is especially common for initiating radical-mediated polymerization reactions, including vinyl chain-growth polymerization, atom transfer radical polymerization, thiol–ene step-growth polymerization, and polymerization via oxidative coupling. While enzyme-mediated polymerization is useful for the production of materials intended for subsequent use, it is especially well-suited for in situ polymerizations, where the polymer is formed in the place where it will be utilized. Such polymerizations are especially useful for biomedical adhesives and for sensing applications. PMID:26848652

  17. Effects of Hofmeister salt series on gluten network formation: Part II. Anion series.

    PubMed

    Tuhumury, H C D; Small, D M; Day, L

    2016-12-01

    Different anion salts from the Hofmeister series were used to investigate their effects on gluten network formation. The effects of these anion salts on the mixing properties of the dough and the rheological and chemical properties of gluten samples extracted from the dough with these respective salts were compared. The aim of this work was to determine how different anion salts influence the formation of the gluten structure during dough mixing. It was found that the Hofmeister anion salts affected the gluten network formation by interacting directly with specific amino acid residues that resulted in changes in gluten protein composition, specifically the percentage of the unextractable polymeric protein fractions (%UPP). These changes consequently led to remarkable differences in the mixing profiles and microstructural features of the dough, small deformation rheological properties of the gluten and a strain hardening behaviour of both dough and gluten samples.

  18. A 3D finite-volume scheme for the Euler equations on adaptive tetrahedral grids

    SciTech Connect

    Vijayan, P.; Kallinderis, Y. )

    1994-08-01

    The paper describes the development and application of a new Euler solver for adaptive tetrahedral grids. Spatial discretization uses a finite-volume, node-based scheme that is of central-differencing type. A second-order Taylor series expansion is employed to march the solution in time according to the Lax-Wendroff approach. Special upwind-like smoothing operators for unstructured grids are developed for shock-capturing, as well as for suppression of solution oscillations. The scheme is formulated so that all operations are edge-based, which reduces the computational effort significantly. An adaptive grid algorithm is employed in order to resolve local flow features. This is achieved by dividing the tetrahedral cells locally, guided by a flow feature detection algorithm. Application cases include transonic flow around the ONERA M6 wing and transonic flow past a transport aircraft configuration. Comparisons with experimental data evaluate accuracy of the developed adaptive solver. 31 refs., 33 figs.

  19. Exploration of tetrahedral structures in silicate cathodes using a motif-network scheme

    PubMed Central

    Zhao, Xin; Wu, Shunqing; Lv, Xiaobao; Nguyen, Manh Cuong; Wang, Cai-Zhuang; Lin, Zijing; Zhu, Zi-Zhong; Ho, Kai-Ming

    2015-01-01

    Using a motif-network search scheme, we studied the tetrahedral structures of the dilithium/disodium transition metal orthosilicates A2MSiO4 with A = Li or Na and M = Mn, Fe or Co. In addition to finding all previously reported structures, we discovered many other different tetrahedral-network-based crystal structures which are highly degenerate in energy. These structures can be classified into structures with 1D, 2D and 3D M-Si-O frameworks. A clear trend of the structural preference in different systems was revealed and possible indicators that affect the structure stabilities were introduced. For the case of Na systems which have been much less investigated in the literature relative to the Li systems, we predicted their ground state structures and found evidence for the existence of new structural motifs. PMID:26497381

  20. Near-field testing of the 5-meter model of the tetrahedral truss antenna

    NASA Technical Reports Server (NTRS)

    Kefauver, Neill; Cencich, Tom; Osborn, Jim; Osmanski, J. T.

    1986-01-01

    This report documents the technical results from near-field testing of the General Dynamics 5-meter model of the tetrahedral truss antenna at the Martin Marietta Denver Aerospace facility. A 5-meter square side of the tetrahedral served as the perimeter of the antenna, and a mesh surface and extensive surface contouring cord network was used to create a parabolic aperture shape to within an rms accuracy of 30 mils or better. Pattern measurements were made with offset feed systems radiating at frequencies of 7.73, 11.60, 2.27, and 4.26 (all in GHz). This report discusses the method of collecting the data, system measurement accuracy, the test data compiled, and diagostics and isolation of causes of pattern results. The technique of using near-field phase for measuring surface mechanical tolerances is included. Detailed far field antenna patterns and their implications are provided for all tests conducted.

  1. Near-field testing of the 5-meter model of the tetrahedral truss antenna

    NASA Astrophysics Data System (ADS)

    Kefauver, Neill; Cencich, Tom; Osborn, Jim; Osmanski, J. T.

    1986-08-01

    This report documents the technical results from near-field testing of the General Dynamics 5-meter model of the tetrahedral truss antenna at the Martin Marietta Denver Aerospace facility. A 5-meter square side of the tetrahedral served as the perimeter of the antenna, and a mesh surface and extensive surface contouring cord network was used to create a parabolic aperture shape to within an rms accuracy of 30 mils or better. Pattern measurements were made with offset feed systems radiating at frequencies of 7.73, 11.60, 2.27, and 4.26 (all in GHz). This report discusses the method of collecting the data, system measurement accuracy, the test data compiled, and diagostics and isolation of causes of pattern results. The technique of using near-field phase for measuring surface mechanical tolerances is included. Detailed far field antenna patterns and their implications are provided for all tests conducted.

  2. Interactive point-based rendering of higher-order tetrahedral data.

    PubMed

    Zhou, Yuan; Garland, Michael

    2006-01-01

    Computational simulations frequently generate solutions defined over very large tetrahedral volume meshes containing many millions of elements. Furthermore, such solutions may often be expressed using non-linear basis functions. Certain solution techniques, such as discontinuous Galerkin methods, may even produce non-conforming meshes. Such data is difficult to visualize interactively, as it is far too large to fit in memory and many common data reduction techniques, such as mesh simplification, cannot be applied to non-conforming meshes. We introduce a point-based visualization system for interactive rendering of large, potentially non-conforming, tetrahedral meshes. We propose methods for adaptively sampling points from non-linear solution data and for decimating points at run time to fit GPU memory limits. Because these are streaming processes, memory consumption is independent of the input size. We also present an order-independent point rendering method that can efficiently render volumes on the order of 20 million tetrahedra at interactive rates.

  3. Exploration of tetrahedral structures in silicate cathodes using a motif-network scheme.

    PubMed

    Zhao, Xin; Wu, Shunqing; Lv, Xiaobao; Nguyen, Manh Cuong; Wang, Cai-Zhuang; Lin, Zijing; Zhu, Zi-Zhong; Ho, Kai-Ming

    2015-10-26

    Using a motif-network search scheme, we studied the tetrahedral structures of the dilithium/disodium transition metal orthosilicates A2MSiO4 with A = Li or Na and M = Mn, Fe or Co. In addition to finding all previously reported structures, we discovered many other different tetrahedral-network-based crystal structures which are highly degenerate in energy. These structures can be classified into structures with 1D, 2D and 3D M-Si-O frameworks. A clear trend of the structural preference in different systems was revealed and possible indicators that affect the structure stabilities were introduced. For the case of Na systems which have been much less investigated in the literature relative to the Li systems, we predicted their ground state structures and found evidence for the existence of new structural motifs.

  4. Exploration of tetrahedral structures in silicate cathodes using a motif-network scheme

    SciTech Connect

    Zhao, Xin; Wu, Shunqing; Lv, Xiaobao; Nguyen, Manh Cuong; Wang, Cai -Zhuang; Lin, Zijing; Zhu, Zi -Zhong; Ho, Kai -Ming

    2015-10-26

    Using a motif-network search scheme, we studied the tetrahedral structures of the dilithium/disodium transition metal orthosilicates A2MSiO4 with A = Li or Na and M = Mn, Fe or Co. In addition to finding all previously reported structures, we discovered many other different tetrahedral-network-based crystal structures which are highly degenerate in energy. In addition, these structures can be classified into structures with 1D, 2D and 3D M-Si-O frameworks. A clear trend of the structural preference in different systems was revealed and possible indicators that affect the structure stabilities were introduced. For the case of Na systems which have been much less investigated in the literature relative to the Li systems, we predicted their ground state structures and found evidence for the existence of new structural motifs.

  5. Investigation of negative-parity states in Dy156 : Search for evidence of tetrahedral symmetry

    DOE PAGES

    Hartley, D. J.; Riedinger, L. L.; Janssens, R. V. F.; ...

    2017-01-01

    An experiment populating low/medium-spin states in 156Dy was performed to investigate the possibility of tetrahedral symmetry in this nucleus. In particular, focus was placed on the low-spin, negative-parity states since recent theoretical studies suggest that these may be good candidates for this high-rank symmetry. The states were produced in the 148Nd(12C,4 n) reaction and the Gammasphere array was utilized to detect the emitted rays. B(E 2) /B(E1) ratios of transition probabilities from the low-spin, negative-parity bands were determined and used to interpret whether these structures are best associated with tetrahedral symmetry or, as previously assigned, to octupole vibrations. Additionally, severalmore » other negative-parity structures were observed to higher spin and two new sequences were established« less

  6. Investigation of negative-parity states in Dy156: Search for evidence of tetrahedral symmetry

    DOE PAGES

    Hartley, D. J.; Riedinger, L. L.; Janssens, R. V. F.; ...

    2017-01-20

    In this paper, an experiment populating low/medium-spin states in 156Dy was performed to investigate the possibility of tetrahedral symmetry in this nucleus. In particular, focus was placed on the low-spin, negative-parity states since recent theoretical studies suggest that these may be good candidates for this high-rank symmetry. The states were produced in the 148Nd(12C,4n) reaction and the Gammasphere array was utilized to detect the emitted γ rays. B(E2)/B(E1) ratios of transition probabilities from the low-spin, negative-parity bands were determined and used to interpret whether these structures are best associated with tetrahedral symmetry or, as previously assigned, to octupole vibrations. Finally,more » in addition, several other negative-parity structures were observed to higher spin and two new sequences were established.« less

  7. Fostering Teacher Development to a Tetrahedral Orientation in the Teaching of Chemistry

    NASA Astrophysics Data System (ADS)

    Lewthwaite, Brian; Wiebe, Rick

    2011-11-01

    This paper reports on the initial outcomes from the end of the fourth year of a 5 year research and professional development project to improve chemistry teaching among three cohorts of chemistry teachers in Manitoba, Canada. The project responds to a new curriculum introduction advocating a tetrahedral orientation (Mahaffy, Journal of Chemical Education 83(1), 49-55, 2006) to the teaching of chemistry. The project in its entirety is based upon several theoretical models in fostering chemistry teacher development (in particular Bronfenbrenner's bio-ecological model). These models are described, as is the progress made by teachers based upon the use of a Chemistry Teacher Inventory and associated teacher responses. Overall, statistical analysis of perceptions of their own teaching and comments made by teachers suggests they are showing limited development towards a tetrahedral orientation, albeit in a manner consistent with the curriculum. Ongoing research-based activities in this project are also described.

  8. 3D level set methods for evolving fronts on tetrahedral meshes with adaptive mesh refinement

    DOE PAGES

    Morgan, Nathaniel Ray; Waltz, Jacob I.

    2017-03-02

    The level set method is commonly used to model dynamically evolving fronts and interfaces. In this work, we present new methods for evolving fronts with a specified velocity field or in the surface normal direction on 3D unstructured tetrahedral meshes with adaptive mesh refinement (AMR). The level set field is located at the nodes of the tetrahedral cells and is evolved using new upwind discretizations of Hamilton–Jacobi equations combined with a Runge–Kutta method for temporal integration. The level set field is periodically reinitialized to a signed distance function using an iterative approach with a new upwind gradient. We discuss themore » details of these level set and reinitialization methods. Results from a range of numerical test problems are presented.« less

  9. 3D level set methods for evolving fronts on tetrahedral meshes with adaptive mesh refinement

    NASA Astrophysics Data System (ADS)

    Morgan, Nathaniel R.; Waltz, Jacob I.

    2017-05-01

    The level set method is commonly used to model dynamically evolving fronts and interfaces. In this work, we present new methods for evolving fronts with a specified velocity field or in the surface normal direction on 3D unstructured tetrahedral meshes with adaptive mesh refinement (AMR). The level set field is located at the nodes of the tetrahedral cells and is evolved using new upwind discretizations of Hamilton-Jacobi equations combined with a Runge-Kutta method for temporal integration. The level set field is periodically reinitialized to a signed distance function using an iterative approach with a new upwind gradient. The details of these level set and reinitialization methods are discussed. Results from a range of numerical test problems are presented.

  10. Preliminary design of a large tetrahedral truss/hexagonal heatshield panel aerobrake

    NASA Technical Reports Server (NTRS)

    Dorsey, John T.; Mikulas, Martin M., Jr.

    1989-01-01

    An aerobrake structural concept is introduced which consists of two primary components: (1) a lightweight erectable tetrahedral support truss; and (2) sandwich hexagonal heatshield panels which, when attached to the truss, form a continuous impermeable aerobraking surface. Generic finite element models and a general analysis procedure to design tetrahedral truss/hexagonal heatshield panel aerobrakes is developed, and values of the aerobrake design parameters which minimize mass and packaging volume for a 120-foot-diameter aerobrake are determined. Sensitivity of the aerobrake design to variations in design parameters is also assessed. The results show that a 120-foot-diameter aerobrake is viable using the concept presented (i.e., the aerobrake mass is less than or equal to 15 percent of the payload spacecraft mass). Minimizing the aerobrake mass (by increasing the number of rings in the support truss) however, leads to aerobrakes with the highest part count.

  11. Low symmetry tetrahedral nematic liquid crystal phases: Ambidextrous chirality and ambidextrous helicity.

    PubMed

    Pleiner, Harald; Brand, Helmut R

    2014-02-01

    We discuss the symmetry properties as well as the dynamic behavior of various non-polar nematic liquid crystal phases with tetrahedral order. We concentrate on systems that show biaxial nematic order coexisting with octupolar (tetrahedral) order. Non-polar examples are phases with D2 and S4 symmetries, which can be characterized as biaxial nematics lacking inversion symmetry. It is this combination that allows for new features in the statics and dynamics of these phases. The D2-symmetric phase is chiral, even for achiral molecules, and shows ambidextrous chirality in all three preferred directions. The achiral S4-symmetric phase allows for ambidextrous helicity, similar to the higher-symmetric D2d-symmetric phase. Such phases are candidates for nematic phases made from banana-shaped molecules.

  12. Exploration of tetrahedral structures in silicate cathodes using a motif-network scheme

    DOE PAGES

    Zhao, Xin; Wu, Shunqing; Lv, Xiaobao; ...

    2015-10-26

    Using a motif-network search scheme, we studied the tetrahedral structures of the dilithium/disodium transition metal orthosilicates A2MSiO4 with A = Li or Na and M = Mn, Fe or Co. In addition to finding all previously reported structures, we discovered many other different tetrahedral-network-based crystal structures which are highly degenerate in energy. In addition, these structures can be classified into structures with 1D, 2D and 3D M-Si-O frameworks. A clear trend of the structural preference in different systems was revealed and possible indicators that affect the structure stabilities were introduced. For the case of Na systems which have been muchmore » less investigated in the literature relative to the Li systems, we predicted their ground state structures and found evidence for the existence of new structural motifs.« less

  13. Atomic Scale Picture of the Ion Conduction Mechanism in Tetrahedral Network of Lanthanum Barium Gallate

    SciTech Connect

    Jalarvo, Niina H; Gourdon, Olivier; Bi, Zhonghe; Gout, Delphine J; Ohl, Michael E; Paranthaman, Mariappan Parans

    2013-01-01

    Combined experimental study of impedance spectroscopy, neutron powder diffraction and quasielastic neutron scattering was performed to shed light into the atomic scale ion migration processes in proton and oxide ion conductor; La0.8Ba1.2GaO3.9 . This material consist of tetrahedral GaO4 units, which are rather flexible and rocking motion of these units promotes the ionic migration process. The oxide ion (vacancy) conduction takes place on channels along c axis, involving a single elementary step, which occurs between adjacent tetrahedron (inter-tetrahedron jump). The proton conduction mechanism consists of intra-tetrahedron and inter-tetrahedron elementary processes. The intra-tetrahedron proton transport is the rate-limiting process, with activation energy of 0.44 eV. The rocking motion of the GaO4 tetrahedron aids the inter-tetrahedral proton transport, which has the activation energy of 0.068 eV.

  14. Investigation of negative-parity states in 156Dy: Search for evidence of tetrahedral symmetry

    NASA Astrophysics Data System (ADS)

    Hartley, D. J.; Riedinger, L. L.; Janssens, R. V. F.; Majola, S. N. T.; Riley, M. A.; Allmond, J. M.; Beausang, C. W.; Carpenter, M. P.; Chiara, C. J.; Cooper, N.; Curien, D.; Gall, B. J. P.; Garrett, P. E.; Kondev, F. G.; Kulp, W. D.; Lauritsen, T.; McCutchan, E. A.; Miller, D.; Miller, S.; Piot, J.; Redon, N.; Sharpey-Schafer, J. F.; Simpson, J.; Stefanescu, I.; Wang, X.; Werner, V.; Wood, J. L.; Yu, C.-H.; Zhu, S.; Dudek, J.

    2017-01-01

    An experiment populating low/medium-spin states in 156Dy was performed to investigate the possibility of tetrahedral symmetry in this nucleus. In particular, focus was placed on the low-spin, negative-parity states since recent theoretical studies suggest that these may be good candidates for this high-rank symmetry. The states were produced in the 148Nd(12C,4 n ) reaction and the Gammasphere array was utilized to detect the emitted γ rays. B (E 2 )/B (E 1 ) ratios of transition probabilities from the low-spin, negative-parity bands were determined and used to interpret whether these structures are best associated with tetrahedral symmetry or, as previously assigned, to octupole vibrations. In addition, several other negative-parity structures were observed to higher spin and two new sequences were established.

  15. Anion transporters and biological systems.

    PubMed

    Gale, Philip A; Pérez-Tomás, Ricardo; Quesada, Roberto

    2013-12-17

    In this Account, we discuss the development of new lipid bilayer anion transporters based on the structure of anionophoric natural products (the prodigiosins) and purely synthetic supramolecular systems. We have studied the interaction of these compounds with human cancer cell lines, and, in general, the most active anion transporter compounds possess the greatest anti-cancer properties. Initially, we describe the anion transport properties of synthetic molecules that are based on the structure of the family of natural products known as the prodiginines. Obatoclax, for example, is a prodiginine derivative with an indole ring that is currently in clinical trials for use as an anti-cancer drug. The anion transport properties of the compounds were correlated with their toxicity toward small cell human lung cancer GLC4 cells. We studied related compounds with enamine moieties, tambjamines, that serve as active transporters. These molecules and others in this series could depolarize acidic compartments within GLC4 cells and trigger apoptosis. In a study of the variation of lipophilicity of a series of these compounds, we observed that, as log P increases, the anion transport efficiency reaches a peak and then decreases. In addition, we discuss the anion transport properties of series of synthetic supramolecular anion receptor species. We synthesized trisureas and thioureas based on the tren backbone, and found that the thiourea compounds effectively transport anions. Fluorination of the pendant phenyl groups in this series of compounds greatly enhances the transport properties. Similar to our earlier results, the most active anion transporters reduced the viability of human cancer cell lines by depolarizing acidic compartments in GLC4 cells and triggering apoptosis. In an attempt to produce simpler transporters that obey Lipinski's Rule of Five, we synthesized simpler systems containing a single urea or thiourea group. Once again the thiourea systems, and in particular

  16. K{sub 2}Ca{sub 6}Si{sub 4}O{sub 15}-structural and spectroscopical studies on a mixed tetrahedral-octahedral framework

    SciTech Connect

    Arroyabe, E.; Kaindl, R.; Toebbens, D.M.; Kahlenberg, V.

    2009-12-15

    In the course of an excursion into the system K{sub 2}O-CaO-SiO{sub 2}, single crystalline material of the previously unknown compound K{sub 2}Ca{sub 6}Si{sub 4}O{sub 15} has been obtained. Single crystal X-ray diffraction experiments revealed that the new phase is monoclinic (space group P12/c1) with the following basic crystallographic data: a=7.3782(8) A, b=5.5677(5) A, c=17.2466(17) A, beta=90.005(8){sup o}, Z=2. According to Liebau's nomenclature, the compound can be classified as a mixed anion silicate containing insular [SiO{sub 4}]-groups as well as [Si{sub 2}O{sub 7}]-dimers in the ratio 2:1, i.e. the crystallochemical formula can be written as K{sub 2}Ca{sub 6}[SiO{sub 4}]{sub 2}[Si{sub 2}O{sub 7}]. The silicate anions are linked by K- and Ca-ions distributed among five different non-tetrahedral M-positions and coordinated by six to eight nearest oxygen neighbors. Alternatively, the structure can be described as a heteropolyhedral framework built up by kroehnkite-type [M(SiO{sub 4}){sub 2}O{sub 2}]-chains in which the MO{sub 6} octahedra are corner-linked to bridging SiO{sub 4} tetrahedra. The chains (running parallel to [0 1 0]) are located in 4.6 A wide layers parallel to (1 0 0). Neighboring sheets are shifted relative to each other by an amount of +delta or -delta along [0 0 1]. In the derived two layer ...ABABAB... stacking sequence, chains belonging to adjacent sheets are linked by corner sharing of common oxygen atoms. The resulting network contains tunnels in which the more irregularly coordinated K- and Ca-ions are incorporated for charge compensation. A comparison between the present compound and structurally related mixed tetrahedral-octahedral frameworks is given. The characterization has been completed by Raman and FTIR-spectroscopy. An allocation of the bands to certain vibrational species has been aided by density functional theory (DFT) calculations. - Abstract: Side view of the whole heteropolyhedral framework in K2Ca6Si4O15. Display

  17. Specific recognition of a tetrahedral phosphonamidate transition state analogue group by a recombinant antibody Fab fragment.

    PubMed

    Hua, T D; Lamaty, F; Souriau, C; Rolland-Fulcrand, V; Lazaro, R; Viallefont, P; Lefranc, M P; Weill, M

    1996-06-01

    In order to obtain antibodies able to catalyse a peptide synthesis, a naive combinatorial library of human Fab antibody fragments was screened with the phosphonamidate transition state analogue of the reaction. Several Fab fragments were able to bind the analogue. Competitive binding studies performed with molecules containing representative parts of the hapten showed that two Fabs were able to recognize specifically the tetrahedral phosphorus present in the hapten.

  18. Anomalous properties of liquids for a family of models with short range tetrahedral interactions

    NASA Astrophysics Data System (ADS)

    Buldyrev, Sergey; Franzese, Giancarlo

    2012-02-01

    Liquids with tetrahedral symmetry of the first coordination shell often display anomalous thermodynamic and dynamic behavior. The main reason for these anomalies is that pressurizing such liquids leads to the disordering of this local symmetry by the particles migrating from the second to the first coordination shell. This in some case may lead to the increase of entropy upon pressurizing and consequently to the volume increase upon cooling. Molecular simulations of various models with tetrahedral symmetry are able to reproduce this anomalous behavior. We study a family of simple models in which we can gradually change the degree of tetrahedrality and investigate the associated changes of the phase diagram by discrete molecular dynamics. A molecule in these models consist of a hard sphere and four point particles attached to the center of the hard sphere by directional bonds arranged in tetrahedral geometry. Each of these four particles has a narrow attractive square well so that the particles belonging to different molecules can attract to each other. We also impose a condition which does not allow a point particle in one molecule to include in its attractive well more than one point particle belonging to different molecules. We investigate how the phase diagram of the system depends on the parameters of the models. None of these models has a liquid -liquid phase transition in the accessible region of the phase. However, adding weak attractive square well to the hard sphere, or wider weak attractive square wells to the point particles can create a liquid-liquid critical point. A comparison with other simple models of the anomalous liquids is made.

  19. A study of pH-dependence of shrink and stretch of tetrahedral DNA nanostructures.

    PubMed

    Wang, Ping; Xia, Zhiwei; Yan, Juan; Liu, Xunwei; Yao, Guangbao; Pei, Hao; Zuo, Xiaolei; Sun, Gang; He, Dannong

    2015-04-21

    We monitored the shrink and stretch of the tetrahedral DNA nanostructure (TDN) and the i-motif connected TDN structure at pH 8.5 and pH 4.5, and we found that not only the i-motif can change its structure when the pH changes, but also the TDN and the DNA double helix change their structures when the pH changes.

  20. Amorphous-amorphous transformation at high pressure in gallo-germanosilicate tetrahedral network glasses

    NASA Astrophysics Data System (ADS)

    Cormier, L.; Ferlat, G.; Itié, J.-P.; Galoisy, L.; Calas, G.; Aquilanti, G.

    2007-10-01

    We report the existence of structurally distinct amorphous states upon compression in sodium gallo-germanosilicate glasses. In situ x-ray absorption spectroscopy provides clear evidence for a transition at high pressure to a more compact arrangement of atoms based on Ga and Ge octahedral sites. This study extends previous works on simple and open tetrahedral networks ( SiO2 and GeO2 ) by showing the compression behavior of stuffed (by Na cations) and mixed network glasses.

  1. A first collision source method for ATTILA, an unstructured tetrahedral mesh discrete ordinates code

    SciTech Connect

    Wareing, T.A.; Morel, J.E.; Parsons, D.K.

    1998-12-01

    A semi-analytic first collision source method is developed for the transport code, ATTILA, a three-dimensional, unstructured tetrahedral mesh, discrete-ordinates code. This first collision source method is intended to mitigate ray effects due to point sources. The method is third-order accurate, which is the same order of accuracy as the linear-discontinuous spatial differencing scheme used in ATTILA. Numerical results are provided to demonstrate the accuracy and efficiency of the first collision source method.

  2. A FAST ITERATIVE METHOD FOR SOLVING THE EIKONAL EQUATION ON TETRAHEDRAL DOMAINS

    PubMed Central

    Fu, Zhisong; Kirby, Robert M.; Whitaker, Ross T.

    2014-01-01

    Generating numerical solutions to the eikonal equation and its many variations has a broad range of applications in both the natural and computational sciences. Efficient solvers on cutting-edge, parallel architectures require new algorithms that may not be theoretically optimal, but that are designed to allow asynchronous solution updates and have limited memory access patterns. This paper presents a parallel algorithm for solving the eikonal equation on fully unstructured tetrahedral meshes. The method is appropriate for the type of fine-grained parallelism found on modern massively-SIMD architectures such as graphics processors and takes into account the particular constraints and capabilities of these computing platforms. This work builds on previous work for solving these equations on triangle meshes; in this paper we adapt and extend previous two-dimensional strategies to accommodate three-dimensional, unstructured, tetrahedralized domains. These new developments include a local update strategy with data compaction for tetrahedral meshes that provides solutions on both serial and parallel architectures, with a generalization to inhomogeneous, anisotropic speed functions. We also propose two new update schemes, specialized to mitigate the natural data increase observed when moving to three dimensions, and the data structures necessary for efficiently mapping data to parallel SIMD processors in a way that maintains computational density. Finally, we present descriptions of the implementations for a single CPU, as well as multicore CPUs with shared memory and SIMD architectures, with comparative results against state-of-the-art eikonal solvers. PMID:25221418

  3. Transport of phase space densities through tetrahedral meshes using discrete flow mapping

    NASA Astrophysics Data System (ADS)

    Bajars, Janis; Chappell, David J.; Søndergaard, Niels; Tanner, Gregor

    2017-01-01

    Discrete flow mapping was recently introduced as an efficient ray based method determining wave energy distributions in complex built up structures. Wave energy densities are transported along ray trajectories through polygonal mesh elements using a finite dimensional approximation of a ray transfer operator. In this way the method can be viewed as a smoothed ray tracing method defined over meshed surfaces. Many applications require the resolution of wave energy distributions in three-dimensional domains, such as in room acoustics, underwater acoustics and for electromagnetic cavity problems. In this work we extend discrete flow mapping to three-dimensional domains by propagating wave energy densities through tetrahedral meshes. The geometric simplicity of the tetrahedral mesh elements is utilised to efficiently compute the ray transfer operator using a mixture of analytic and spectrally accurate numerical integration. The important issue of how to choose a suitable basis approximation in phase space whilst maintaining a reasonable computational cost is addressed via low order local approximations on tetrahedral faces in the position coordinate and high order orthogonal polynomial expansions in momentum space.

  4. Tetrahedral Finite-Volume Solutions to the Navier-Stokes Equations on Complex Configurations

    NASA Technical Reports Server (NTRS)

    Frink, Neal T.; Pirzadeh, Shahyar Z.

    1998-01-01

    A review of the algorithmic features and capabilities of the unstructured-grid flow solver USM3Dns is presented. This code, along with the tetrahedral grid generator, VGRIDns, is being extensively used throughout the U.S. for solving the Euler and Navier-Stokes equations on complex aerodynamic problems. Spatial discretization is accomplished by a tetrahedral cell-centered finite-volume formulation using Roe's upwind flux difference splitting. The fluxes are limited by either a Superbee or MinMod limiter. Solution reconstruction within the tetrahedral cells is accomplished with a simple, but novel, multidimensional analytical formula. Time is advanced by an implicit backward-Euler time-stepping scheme. Flow turbulence effects are modeled by the Spalart-Allmaras one-equation model, which is coupled with a wall function to reduce the number of cells in the near-wall region of the boundary layer. The issues of accuracy and robustness of USM3Dns Navier-Stokes capabilities are addressed for a flat-plate boundary layer, and a full F-16 aircraft with external stores at transonic speed.

  5. Simulation of Stagnation Region Heating in Hypersonic Flow on Tetrahedral Grids

    NASA Technical Reports Server (NTRS)

    Gnoffo, Peter A.

    2007-01-01

    Hypersonic flow simulations using the node based, unstructured grid code FUN3D are presented. Applications include simple (cylinder) and complex (towed ballute) configurations. Emphasis throughout is on computation of stagnation region heating in hypersonic flow on tetrahedral grids. Hypersonic flow over a cylinder provides a simple test problem for exposing any flaws in a simulation algorithm with regard to its ability to compute accurate heating on such grids. Such flaws predominantly derive from the quality of the captured shock. The importance of pure tetrahedral formulations are discussed. Algorithm adjustments for the baseline Roe / Symmetric, Total-Variation-Diminishing (STVD) formulation to deal with simulation accuracy are presented. Formulations of surface normal gradients to compute heating and diffusion to the surface as needed for a radiative equilibrium wall boundary condition and finite catalytic wall boundary in the node-based unstructured environment are developed. A satisfactory resolution of the heating problem on tetrahedral grids is not realized here; however, a definition of a test problem, and discussion of observed algorithm behaviors to date are presented in order to promote further research on this important problem.

  6. Ultrahigh-Resolution {gamma}-Ray Spectroscopy of {sup 156}Gd: A Test of Tetrahedral Symmetry

    SciTech Connect

    Jentschel, M.; Krempel, J.; Urban, W.; Tonev, D.; Petkov, P.; Dudek, J.; Curien, D.; Lauss, B.; Angelis, G. de

    2010-06-04

    Tetrahedral symmetry in strongly interacting systems would establish a new class of quantum effects at subatomic scale. Excited states in {sup 156}Gd that could carry the information about the tetrahedral symmetry were populated in the {sup 155}Gd(n,{gamma}){sup 156}Gd reaction and studied using the GAMS4/5 Bragg spectrometers at the Institut Laue-Langevin. We have identified the 5{sub 1}{sup -{yields}}3{sub 1}{sup -} transition of 131.983(12) keV in {sup 156}Gd and determined its intensity to be 1.9(3)x10{sup -6} per neutron capture. The lifetime {tau}=220{sub -30}{sup +180}fs of the 5{sub 1}{sup -} state in {sup 156}Gd has been measured using the GRID technique. The resulting B(E2)=293{sub -134}{sup +61}Weisskopf unit rate of the 131.983 keV transition provides the intrinsic quadrupole moment of the 5{sub 1}{sup -} state in {sup 156}Gd to be Q{sub 0}=7.1{sub -1.6}{sup +0.7} b. This large value, comparable to the quadrupole moment of the ground state in {sup 156}Gd, gives strong evidence against tetrahedral symmetry in the lowest odd-spin, negative-parity band of {sup 156}Gd.

  7. A FAST ITERATIVE METHOD FOR SOLVING THE EIKONAL EQUATION ON TETRAHEDRAL DOMAINS.

    PubMed

    Fu, Zhisong; Kirby, Robert M; Whitaker, Ross T

    2013-01-01

    Generating numerical solutions to the eikonal equation and its many variations has a broad range of applications in both the natural and computational sciences. Efficient solvers on cutting-edge, parallel architectures require new algorithms that may not be theoretically optimal, but that are designed to allow asynchronous solution updates and have limited memory access patterns. This paper presents a parallel algorithm for solving the eikonal equation on fully unstructured tetrahedral meshes. The method is appropriate for the type of fine-grained parallelism found on modern massively-SIMD architectures such as graphics processors and takes into account the particular constraints and capabilities of these computing platforms. This work builds on previous work for solving these equations on triangle meshes; in this paper we adapt and extend previous two-dimensional strategies to accommodate three-dimensional, unstructured, tetrahedralized domains. These new developments include a local update strategy with data compaction for tetrahedral meshes that provides solutions on both serial and parallel architectures, with a generalization to inhomogeneous, anisotropic speed functions. We also propose two new update schemes, specialized to mitigate the natural data increase observed when moving to three dimensions, and the data structures necessary for efficiently mapping data to parallel SIMD processors in a way that maintains computational density. Finally, we present descriptions of the implementations for a single CPU, as well as multicore CPUs with shared memory and SIMD architectures, with comparative results against state-of-the-art eikonal solvers.

  8. Brønsted versus Lewis Acid Type Anion Recognition by Arylboronic Acids.

    PubMed

    Martínez-Aguirre, Mayte A; Yatsimirsky, Anatoly K

    2015-05-15

    Interactions between arylboronic acids and a series of anions as tetrabutylammonium salts in DMSO and MeCN were studied by (1)H and (11)B NMR as well as spectrophotometrically. Boronic acids act as Brønsted acid type receptors through hydrogen bonding with B(OH)2 hydroxyl groups toward Cl(-), Br(-), HSO4(-), and AcO(-), but they act as Lewis acid type receptors toward F(-) and H2PO4(-), which form tetrahedral adducts with the B(III) center of boronic acids, although there is also evidence for some contribution of hydrogen bonding with these anions. The Hammett plot for the binding constants of AcO(-) with 3- and 4-substituted phenylboronic acids in DMSO is nonlinear, with a small negative slope for electron-donating and weakly electron-accepting substituents and a large positive slope for strongly electron-accepting substituents. 3-Nitrophenylboronic acid recognizes zwitterions of amino acids in DMSO, and its UV absorption maximum undergoes a significant red shift in the presence of acetate anions, providing a means for sensing anions optically. Arylboronic acids as Brønsted acid type receptors show relatively low sensitivity to solvent polarity and are equally or even more efficient than widely employed proton donors such as ureas or dicarboxamides.

  9. Photo-responsive polymeric micelles.

    PubMed

    Huang, Yu; Dong, Ruijiao; Zhu, Xinyuan; Yan, Deyue

    2014-09-07

    Photo-responsive polymeric micelles have received increasing attention in both academic and industrial fields due to their efficient photo-sensitive nature and unique nanostructure. In view of the photo-reaction mechanism, photo-responsive polymeric micelles can be divided into five major types: (1) photoisomerization polymeric micelles, (2) photo-induced rearrangement polymeric micelles, (3) photocleavage polymeric micelles, (4) photo-induced crosslinkable polymeric micelles, and (5) photo-induced energy conversion polymeric micelles. This review highlights the recent advances of photo-responsive polymeric micelles, including the design, synthesis and applications in various biomedical fields. Especially, the influence of different photo-reaction mechanisms on the morphology, structure and properties of the polymeric micelles is emphasized. Finally, the possible future directions and perspectives in this emerging area are briefly discussed.

  10. Bound anionic states of adenine

    SciTech Connect

    Haranczyk, Maciej; Gutowski, Maciej S; Li, Xiang; Bowen, Kit H

    2007-03-20

    Anionic states of nucleic acid bases are involved in DNA damage by low-energy electrons and in charge transfer through DNA. Previous gas phase studies of free, unsolvated nucleic acid base parent anions probed only dipole-bound states, which are not present in condensed phase environments, but did not observe valence anionic states, which for purine bases, are thought to be adiabatically unbound. Contrary to this expectation, we have demonstrated that some thus far ignored tautomers of adenine, which result from enamine-imine transformations, support valence anionic states with electron vertical detachment energies as large as 2.2 eV, and at least one of these anionic tautomers is adiabatically bound. Moreover, we predict that the new anionic tautomers should also dominate in solutions and should be characterized by larger values of electron vertical detachment energy than the canonical valence anion. All of the new-found anionic tautomers might be formed in the course of dissociative electron attachment followed by a hydrogen atom attachment to a carbon atom, and they might affect the structure and properties of DNA and RNA exposed to low-energy electrons. The discovery of these valence anionic states of adenine was facilitated by the development of: (i) a new experimental method for preparing parent anions of nucleic acid bases for photoelectron experiments, and (ii) a new combinatorial/ quantum chemical approach for identification of the most stable tautomers of organic molecules. The computational portion of this work was supported by the: (i) Polish State Committee for Scientific Research (KBN) Grants: DS/8000-4-0140-7 (M.G.) and N204 127 31/2963 (M.H.), (ii) European Social Funds (EFS) ZPORR/2.22/II/2.6/ARP/U/2/05 (M.H.), and (iii) US DOE Office of Biological and Environmental Research, Low Dose Radiation Research Program (M.G.). M.H. holds the Foundation for Polish Science (FNP) award for young scientists. The calculations were performed at the Academic

  11. On the influence of tetrahedral covalent-hybridization on electronic band structure of topological insulators from first principles

    SciTech Connect

    Zhang, X. M.; Xu, G. Z.; Liu, E. K.; Wang, W. H. Wu, G. H.; Liu, Z. Y.

    2015-01-28

    Based on first-principles calculations, we investigate the influence of tetrahedral covalent-hybridization between main-group and transition-metal atoms on the topological band structures of binary HgTe and ternary half-Heusler compounds, respectively. Results show that, for the binary HgTe, when its zinc-blend structure is artificially changed to rock-salt one, the tetrahedral covalent-hybridization will be removed and correspondingly the topologically insulating band character lost. While for the ternary half-Heusler system, the strength of covalent-hybridization can be tuned by varying both chemical compositions and atomic arrangements, and the competition between tetrahedral and octahedral covalent-hybridization has been discussed in details. As a result, we found that a proper strength of tetrahedral covalent-hybridization is probably in favor to realizing the topologically insulating state with band inversion occurring at the Γ point of the Brillouin zone.

  12. Geometric multigrid to accelerate the solution of the quasi-static electric field problem by tetrahedral finite elements.

    PubMed

    Hollaus, K; Weiss, B; Magele, Ch; Hutten, H

    2004-02-01

    The acceleration of the solution of the quasi-static electric field problem considering anisotropic complex conductivity simulated by tetrahedral finite elements of first order is investigated by geometric multigrid.

  13. Specific solubility behavior of quaternary ammonium-based poly(ionic liquid) particles by changing counter anion.

    PubMed

    Tokuda, Masayoshi; Minami, Hideto

    2013-05-15

    The solubility behavior of poly(ionic liquid) (PIL) particles, which were prepared by dispersion polymerization of ([2-(methacryloyloxy)ethyl]trimethylammonium bis(trifluoromethanesulfonyl)amide), [MTMA][TFSA], was observed in detail. The solubility of PILs was varied by changing the counter anion. A PIL with [TFSA] anion does not dissolve in polar solvents such as ethanol; however, a PIL with Br anions does dissolve in ethanol. Upon the addition of LiBr to ethanol solution at high concentrations (>2.5 wt.%), the PIL particles dissolved from their outer surface and the counter anions [TFSA] were replaced with Br anions on the particle surfaces. On the other hand, in the case of the ethanol solutions at low LiBr concentrations (<2.5 wt.%), a specific solubility behavior was observed: domains inside the PIL particles were generated before their dissolution, most likely due to osmotic pressure. Moreover, PIL particles having hollow structures were prepared using this specific solubility behavior.

  14. Tetrahedral lander

    NASA Technical Reports Server (NTRS)

    Roberts, Michael L. (Inventor)

    1993-01-01

    An apparatus and method is disclosed for decelerating and absorbing impact of a re-entry vehicle suitable for payloads that are relatively light as well as payloads weighing several tons or more. The apparatus includes four inflatable legs displaced equidistantly from each other around a capsule or housing which contains a payload. The legs are inflated at a designated altitude after entering earth's atmosphere to slow the descent of the re-entry vehicle. Connected between each of the four legs are drag inducing surfaces that deploy as the legs inflate. The drag inducing surfaces are triangularly shaped with one such surface being connected between each pair of legs for a total of six drag inducing surfaces. The legs have drag inducing outer surfaces which act to slow the descent of the re-entry vehicle.

  15. Lipase-catalyzed ring-opening polymerization of lactones to polyesters and its mechanistic aspects.

    PubMed

    Namekawa, S; Suda, S; Uyama, H; Kobayashi, S

    1999-01-01

    Lipase catalysis induced a ring-opening polymerization of lactones with different ring-sizes. Small-size (four-membered) and medium-size lactones (six- and seven-membered) as well as macrolides (12-, 13-, 16-, and 17-membered) were subjected to lipase-catalyzed polymerization. The polymerization behaviors depended primarily on the lipase origin and the monomer structure. The macrolides showing much lower anionic polymerizability were enzymatically polymerized faster than epsilon-caprolactone. The granular immobilized lipase derived from Candida antartica showed extremely efficient catalysis in the polymerization of epsilon-caprolactone. Single-step terminal functionalization of the polyester was achieved by initiator and terminator methods. The enzymatic polymerizability of lactones was quantitatively evaluated by Michaelis-Menten kinetics.

  16. Influence of the Rigid Connection Between Discs in the Tetrahedral Prisms on Equivalent Stresses When Cutting Work Faces

    NASA Astrophysics Data System (ADS)

    Khoreshok, A. A.; Mametyev, L. E.; Borisov, A. Yu; Vorobyev, A. V.

    2016-04-01

    This paper presents the results of modeling of the stressed state of structural elements of the paired fastening points of the two disc tools to the tetrahedral prisms of the working bodies of the roadheaders of selective action when cutting work faces of heterogeneous structure. The advantages of cooperative mode rotation to separate two disc tools on each of the tetrahedral prisms placed between the axial cutting crowns.

  17. Hydrogen in anion vacancies of semiconductors

    SciTech Connect

    Du, Mao-Hua; Singh, David J

    2009-01-01

    Density functional calculations show that, depending on the anion size, hydrogen in anion vacancies of various II-VI semiconductors can be either two-fold or four-fold coordinated, and has either amphoteric or shallow donor character. In general, the multi-coordination of hydrogen in an anion vacancy is the indication of an anionic H, H { ion, in the relatively ionic environment. In more covalent semiconductors, H would form a single cation-H bond in the anion vacancy.

  18. Radiation stability of anion-exchange resins based on epichlorohydrin and vinylpyridines

    SciTech Connect

    Zainutdinov, S.S.; Dzhalilov, A.T.; Askarov, M.A.

    1983-02-01

    The vigorous development of nuclear technology and atomic energy and the hydrometallurgy of the rare and radioactive metals has made it necessary to create and use ion-exchange materials possessing a high resistance to the action of ionizing radiations and the temperature. In view of this, the necessity has arisen for obtaining ion-exchange materials possessing adequate radiation stability. The results of an investigation of the radiation stability of anion-exchange resins based on the products of spontaneous polymerization in the interaction of epichlorohydrin with vinylpyridines show that they possess higher radiation resistance than the industrial anion-exchange resin AN-31 used at the present time.

  19. New approach based on tetrahedral-mesh geometry for accurate 4D Monte Carlo patient-dose calculation

    NASA Astrophysics Data System (ADS)

    Han, Min Cheol; Yeom, Yeon Soo; Kim, Chan Hyeong; Kim, Seonghoon; Sohn, Jason W.

    2015-02-01

    In the present study, to achieve accurate 4D Monte Carlo dose calculation in radiation therapy, we devised a new approach that combines (1) modeling of the patient body using tetrahedral-mesh geometry based on the patient’s 4D CT data, (2) continuous movement/deformation of the tetrahedral patient model by interpolation of deformation vector fields acquired through deformable image registration, and (3) direct transportation of radiation particles during the movement and deformation of the tetrahedral patient model. The results of our feasibility study show that it is certainly possible to construct 4D patient models (= phantoms) with sufficient accuracy using the tetrahedral-mesh geometry and to directly transport radiation particles during continuous movement and deformation of the tetrahedral patient model. This new approach not only produces more accurate dose distribution in the patient but also replaces the current practice of using multiple 3D voxel phantoms and combining multiple dose distributions after Monte Carlo simulations. For routine clinical application of our new approach, the use of fast automatic segmentation algorithms is a must. In order to achieve, simultaneously, both dose accuracy and computation speed, the number of tetrahedrons for the lungs should be optimized. Although the current computation speed of our new 4D Monte Carlo simulation approach is slow (i.e. ~40 times slower than that of the conventional dose accumulation approach), this problem is resolvable by developing, in Geant4, a dedicated navigation class optimized for particle transportation in tetrahedral-mesh geometry.

  20. New approach based on tetrahedral-mesh geometry for accurate 4D Monte Carlo patient-dose calculation.

    PubMed

    Han, Min Cheol; Yeom, Yeon Soo; Kim, Chan Hyeong; Kim, Seonghoon; Sohn, Jason W

    2015-02-21

    In the present study, to achieve accurate 4D Monte Carlo dose calculation in radiation therapy, we devised a new approach that combines (1) modeling of the patient body using tetrahedral-mesh geometry based on the patient's 4D CT data, (2) continuous movement/deformation of the tetrahedral patient model by interpolation of deformation vector fields acquired through deformable image registration, and (3) direct transportation of radiation particles during the movement and deformation of the tetrahedral patient model. The results of our feasibility study show that it is certainly possible to construct 4D patient models (= phantoms) with sufficient accuracy using the tetrahedral-mesh geometry and to directly transport radiation particles during continuous movement and deformation of the tetrahedral patient model. This new approach not only produces more accurate dose distribution in the patient but also replaces the current practice of using multiple 3D voxel phantoms and combining multiple dose distributions after Monte Carlo simulations. For routine clinical application of our new approach, the use of fast automatic segmentation algorithms is a must. In order to achieve, simultaneously, both dose accuracy and computation speed, the number of tetrahedrons for the lungs should be optimized. Although the current computation speed of our new 4D Monte Carlo simulation approach is slow (i.e. ~40 times slower than that of the conventional dose accumulation approach), this problem is resolvable by developing, in Geant4, a dedicated navigation class optimized for particle transportation in tetrahedral-mesh geometry.

  1. Organic anion uptake by hepatocytes.

    PubMed

    Wolkoff, Allan W

    2014-10-01

    Many of the compounds taken up by the liver are organic anions that circulate tightly bound to protein carriers such as albumin. The fenestrated sinusoidal endothelium of the liver permits these compounds to have access to hepatocytes. Studies to characterize hepatic uptake of organic anions through kinetic analyses, suggested that it was carrier-mediated. Attempts to identify specific transporters by biochemical approaches were largely unsuccessful and were replaced by studies that utilized expression cloning. These studies led to identification of the organic anion transport proteins (oatps), a family of 12 transmembrane domain glycoproteins that have broad and often overlapping substrate specificities. The oatps mediate Na(+)-independent organic anion uptake. Other studies identified a seven transmembrane domain glycoprotein, Na(+)/taurocholate transporting protein (ntcp) as mediating Na(+)-dependent uptake of bile acids as well as other organic anions. Although mutations or deficiencies of specific members of the oatp family have been associated with transport abnormalities, there have been no such reports for ntcp, and its physiologic role remains to be determined, although expression of ntcp in vitro recapitulates the characteristics of Na(+)-dependent bile acid transport that is seen in vivo. Both ntcp and oatps traffic between the cell surface and intracellular vesicular pools. These vesicles move through the cell on microtubules, using the microtubule based motors dynein and kinesins. Factors that regulate this motility are under study and may provide a unique mechanism that can alter the plasma membrane content of these transporters and consequently their accessibility to circulating ligands.

  2. Organic Anion Uptake by Hepatocytes

    PubMed Central

    Wolkoff, Allan W.

    2016-01-01

    Many of the compounds taken up by the liver are organic anions that circulate tightly bound to protein carriers such as albumin. The fenestrated sinusoidal endothelium of the liver permits these compounds to have access to hepatocytes. Studies to characterize hepatic uptake of organic anions through kinetic analyses, suggested that it was carrier-mediated. Attempts to identify specific transporters by biochemical approaches were largely unsuccessful and were replaced by studies that utilized expression cloning. These studies led to identification of the organic anion transport proteins (oatps), a family of 12 transmembrane domain glycoproteins that have broad and often overlapping substrate specificities. The oatps mediate Na+-independent organic anion uptake. Other studies identified a seven transmembrane domain glycoprotein, Na+/taurocholate transporting protein (ntcp) as mediating Na+-dependent uptake of bile acids as well as other organic anions. Although mutations or deficiencies of specific members of the oatp family have been associated with transport abnormalities, there have been no such reports for ntcp, and its physiologic role remains to be determined, although expression of ntcp in vitro recapitulates the characteristics of Na+-dependent bile acid transport that is seen in vivo. Both ntcp and oatps traffic between the cell surface and intracellular vesicular pools. These vesicles move through the cell on microtubules, using the microtubule based motors dynein and kinesins. Factors that regulate this motility are under study and may provide a unique mechanism that can alter the plasma membrane content of these transporters and consequently their accessibility to circulating ligands. PMID:25428858

  3. Pu Anion Exchange Process Intensification

    SciTech Connect

    Taylor-Pashow, K.

    2015-10-08

    This project seeks to improve the efficiency of the plutonium anion-exchange process for purifying Pu through the development of alternate ion-exchange media. The objective of the project in FY15 was to develop and test a porous foam monolith material that could serve as a replacement for the current anion-exchange resin, Reillex® HPQ, used at the Savannah River Site (SRS) for purifying Pu. The new material provides advantages in efficiency over the current resin by the elimination of diffusive mass transport through large granular resin beads. By replacing the large resin beads with a porous foam there is much more efficient contact between the Pu solution and the anion-exchange sites present on the material. Several samples of a polystyrene based foam grafted with poly(4-vinylpyridine) were prepared and the Pu sorption was tested in batch contact tests.

  4. Anions in Nucleic Acid Crystallography.

    PubMed

    D'Ascenzo, Luigi; Auffinger, Pascal

    2016-01-01

    Nucleic acid crystallization buffers contain a large variety of chemicals fitting specific needs. Among them, anions are often solely considered for pH-regulating purposes and as cationic co-salts while their ability to directly bind to nucleic acid structures is rarely taken into account. Here we review current knowledge related to the use of anions in crystallization buffers along with data on their biological prevalence. Chloride ions are frequently identified in crystal structures but display low cytosolic concentrations. Hence, they are thought to be distant from nucleic acid structures in the cell. Sulfate ions are also frequently identified in crystal structures but their localization in the cell remains elusive. Nevertheless, the characterization of the binding properties of these ions is essential for better interpreting the solvent structure in crystals and consequently, avoiding mislabeling of electron densities. Furthermore, understanding the binding properties of these anions should help to get clues related to their potential effects in crowded cellular environments.

  5. Tetrahedrally coordinated disordered Cu2SnS3-Cu2ZnSnS4-ZnS alloys with tunable optical and electronic properties

    SciTech Connect

    Erslev, Peter T.; Young, Matthew R.; Li, Jian V.; Siah, Sin Cheng; Chakraborty, Rupak; Du, Hui; Lad, Robert J.; Buonassisi, Tonio; Teeter, Glenn

    2014-08-28

    A key requirement for large-scale deployment of photovoltaic technologies is the development of highly functional materials with controllable opto-electronic properties. In this work, we report on the room-temperature synthesis of disordered alloys of the Earth-abundant, tetrahedrally coordinated semiconductors Cu2SnS3, Cu2ZnSnS4 (CZTS), and ZnS as (Cu2SnS3)1-x(ZnS)x. The resulting disordered semiconductors are found to have continuously and independently tunable optical and electronic properties. Quasi-isovalent alloying on the cation sublattice allows the optical band gap to be varied continuously from 1.1 eV to 2.8 eV. Aliovalent alloying leads to independent control of carrier concentration over at least three orders of magnitude. A conceptual framework describing these disordered materials is presented, in which the structural disorder, constrained by local tetrahedral coordination of both anions and cations, leads to the observed high degree of tunability of the opto-electronic properties. These materials are not only independently interesting, but the developed framework also applies to the opto-electronic properties of kesterite CZTS materials as well as provides a basis for the development of new semiconductors.

  6. Organic-inorganic compounds with strong nonlinear optical properties based on 2,4,6-trimethylpyridinium and tetrahedral BF4- networks

    NASA Astrophysics Data System (ADS)

    Wojtaś, Maciej; Bil, Andrzej; Jakubas, Ryszard; Gągor, Anna; Pietraszko, Adam; Czupiński, Olaf; Tylczyński, Zbigniew; Isakov, Dmitry

    2011-04-01

    A different organic-inorganic crystal—[2,4,6-trimethylpyridinium][BF4]—of nonlinear optical properties at room temperature was synthesized and characterized. The compound is built up of the organic [2,4,6-trimethylpyridinium] cations incorporated into inorganic, tetrahedral BF4 anions. It crystallizes at room temperature in the polar space group Pmn21, and undergoes three first-order phase transitions at [cooling (heating)] 241 (245) K, 297 (328) K, and 389 (406) K. The lowest temperature ferroic phase transition (ferroelastic; mm2→m type) is related to the significant pyroelectric effect. The compound was studied by single-crystal x-ray diffraction at several temperatures, using thermal (differential scanning calorimetry and thermogravimetric analysis) methods and dielectric spectroscopy. The piezoelectric, pyroelectric, and second-harmonic generation (SHG) properties were determined. Density-functional theory calculations in two stable phases are given. The [2,4,6-trimethylpyridinium][BF4] crystal exhibits a SHG efficiency of 1.7 times that of KDP. The mechanism of structural phase transitions in the title compound is discussed.

  7. Variable Effect during Polymerization

    ERIC Educational Resources Information Center

    Lunsford, S. K.

    2005-01-01

    An experiment performing the polymerization of 3-methylthiophene(P-3MT) onto the conditions for the selective electrode to determine the catechol by using cyclic voltammetry was performed. The P-3MT formed under optimized conditions improved electrochemical reversibility, selectivity and reproducibility for the detection of the catechol.

  8. Flame retardant polymeric materials

    SciTech Connect

    Lewin, M.; Atlas, S.M.; Pearce, E.M.

    1982-01-01

    The flame retardation of polyolefins is the focus of this volume. Methods for reduction of smoke and experimental evaluation of flammability parameters for polymeric materials are discussed. The flammability evaluation methods for textiles and the use of mass spectrometry for analysis of polymers and their degradation products are also presented.

  9. Polymerized and functionalized triglycerides

    USDA-ARS?s Scientific Manuscript database

    Plant oils are useful sustainable raw materials for the development of new chemical products. As part of our research emphasis in sustainability and green polymer chemistry, we have explored a new method for polymerizing epoxidized triglycerides with the use of fluorosulfonic acid. Depending on the ...

  10. Variable Effect during Polymerization

    ERIC Educational Resources Information Center

    Lunsford, S. K.

    2005-01-01

    An experiment performing the polymerization of 3-methylthiophene(P-3MT) onto the conditions for the selective electrode to determine the catechol by using cyclic voltammetry was performed. The P-3MT formed under optimized conditions improved electrochemical reversibility, selectivity and reproducibility for the detection of the catechol.

  11. Protein specific polymeric immunomicrospheres

    NASA Technical Reports Server (NTRS)

    Rembaum, Alan (Inventor); Yen, Shiao-Ping S. (Inventor); Dreyer, William J. (Inventor)

    1980-01-01

    Small, round, bio-compatible microspheres capable of covalently bonding proteins and having a uniform diameter below about 3500 A are prepared by substantially instantaneously initiating polymerization of an aqueous emulsion containing no more than 35% total monomer including an acrylic monomer substituted with a covalently bondable group such as hydroxyl, amino or carboxyl and a minor amount of a cross-linking agent.

  12. The effects of non-ionic polymeric surfactants on the cleaning of biofouled hydrogel materials.

    PubMed

    Guan, Allan; Li, Zhenyu; Phillips, K Scott

    2015-01-01

    Block co-polymer surfactants have been used for cleaning hydrogel medical devices that contact the body (e.g., contact lenses) because of their biocompatibility. This work examined the relationship between concentration and detergency of two non-ionic polymeric surfactants (Pluronic F127 and Triton X-100) for cleaning protein soil, with anionic surfactants (sodium dodecyl sulfate and sodium laureth sulfate) as positive controls. Surface plasmon resonance was used to quantify removal of simulated tear soil from self-assembled monolayer surfaces, and a microplate format was used to study the removal of fluorescently labeled soil proteins from contact lenses. While detergency increased as a function of concentration for anionic surfactants, it decreased with concentration for the two polymeric surfactants. The fact that the protein detergency of some non-ionic polymeric surfactants did not increase with concentration above the critical micelle concentration could have implications for optimizing the tradeoff between detergency and biocompatibility.

  13. Stereocontrolled Self-Assembly and Self-Sorting of Luminescent Europium Tetrahedral Cages.

    PubMed

    Yan, Liang-Liang; Tan, Chun-Hong; Zhang, Guang-Lu; Zhou, Li-Peng; Bünzli, Jean-Claude; Sun, Qing-Fu

    2015-07-08

    Coordination-directed self-assembly has become a well-established technique for the construction of functional supramolecular structures. In contrast to the most often exploited transition metals, trivalent lanthanides Ln(III) have been less utilized in the design of polynuclear self-assembled structures despite the wealth of stimulating applications of these elements. In particular, stereochemical control in the assembly of lanthanide chiral cage compounds is not easy to achieve in view of the usually large lability of the Ln(III) ions. We report here the first examples of stereoselective self-assembly of chiral luminescent europium coordination tetrahedral cages and their intriguing self-sorting behavior. Two pairs of R and S ligands are designed on the basis of the pyridine-2,6-dicarboxamide coordination unit, bis(tridentate) L1 and tris(tridentate) L2. Corresponding chiral Eu4(L1)6 and Eu4(L2)4 topological tetrahedral cages are independently assembled via edge- and face-capping design strategies, respectively. The chirality of the ligand is transferred during the self-assembly process to give either Δ or Λ metal stereochemistry. The self-assembled cages are characterized by NMR, high-resolution ESI-TOF-MS, and in one case by X-ray crystallography. Strict control of stereoselectivity is confirmed by CD spectroscopy and NMR enantiomeric differentiation experiments. Narcissistic self-sorting is observed in the self-assembly process when two differently shaped ligands L1 and L2 are mixed. More impressively, distinct self-sorting behavior between Eu4(L1)6 and Eu4(L2)4 coordination cages is observed for the first time when racemic mixtures of ligands are used. We envisage that chiral luminescent lanthanide tetrahedral cages could be used in chiroptical probes\\sensors and enantioselective catalysis.

  14. Island of Rare Earth Nuclei with Tetrahedral and Octahedral Symmetries: Possible Experimental Evidence

    SciTech Connect

    Dudek, J.; Dubray, N.; Pangon, V.; Dobaczewski, J.; Olbratowski, P.; Schunck, N.

    2006-08-18

    Calculations using realistic mean-field methods suggest the existence of nuclear shapes with tetrahedral T{sub d} and/or octahedral O{sub h} symmetries sometimes at only a few hundreds of keV above the ground states in some rare earth nuclei around {sup 156}Gd and {sup 160}Yb. The underlying single-particle spectra manifest exotic fourfold rather than Kramers's twofold degeneracies. The associated shell gaps are very strong, leading to a new form of shape coexistence in many rare earth nuclei. We present possible experimental evidence of the new symmetries based on the published experimental results--although an unambiguous confirmation will require dedicated experiments.

  15. A ROBUST ARBITRARILY HIGH ORDER TRANSPORT METHOD OF THE CHARACTERISTIC TYPE FOR UNSTRUCTURED TETRAHEDRAL GRIDS

    SciTech Connect

    R. M. Ferrer; Y. Y. Azmy

    2009-05-01

    We present a robust arbitrarily high order transport method of the characteristic type for unstructured tetrahedral grids. Previously encountered difficulties have been addressed through the reformulation of the method based on coordinate transformations, evaluation of the moments balance relation as a linear system of equations involving the expansion coefficients of the projected basis, and the asymptotic expansion of the integral kernels in the thin cell limit. The proper choice of basis functions for the high-order spatial expansion of the solution is discussed and its effect on problems involving scattering discussed. Numerical tests are presented to illustrate the beneficial effect of these improvements, and the improved robustness they yield.

  16. Preliminary design of a large tetrahedral truss/hexagonal panel aerobrake structural system

    NASA Technical Reports Server (NTRS)

    Dorsey, John T.; Mikulas, Martin M., Jr.

    1990-01-01

    This paper introduces an aerobrake structural concept consisting of two primary components: (1) a lightweight erectable tetrahedral support truss, and (2) a heatshield composed of individual sandwich hexagonal panels which, when attached to the truss, function as a continuous aerobraking surface. A general preliminary analysis procedure to design the aerobrake components is developed, and values of the aerobrake design parameters which minimize the mass and packaging volume for a 120-foot-diameter aerobrake are determined. Sensitivity of the aerobrake design to variations in design parameters is also assessed.

  17. Preliminary design of a large tetrahedral truss/hexagonal panel aerobrake structural system

    NASA Technical Reports Server (NTRS)

    Dorsey, John T.; Mikulas, Martin M., Jr.

    1990-01-01

    This paper introduces an aerobrake structural concept consisting of two primary components: (1) a lightweight erectable tetrahedral support truss, and (2) a heatshield composed of individual sandwich hexagonal panels which, when attached to the truss, function as a continuous aerobraking surface. A general preliminary analysis procedure to design the aerobrake components is developed, and values of the aerobrake design parameters which minimize the mass and packaging volume for a 120-foot-diameter aerobrake are determined. Sensitivity of the aerobrake design to variations in design parameters is also assessed.

  18. Tetrahedral-Mesh Simulation of Turbulent Flows with the Space-Time Conservative Schemes

    NASA Technical Reports Server (NTRS)

    Chang, Chau-Lyan; Venkatachari, Balaji; Cheng, Gary C.

    2015-01-01

    Direct numerical simulations of turbulent flows are predominantly carried out using structured, hexahedral meshes despite decades of development in unstructured mesh methods. Tetrahedral meshes offer ease of mesh generation around complex geometries and the potential of an orientation free grid that would provide un-biased small-scale dissipation and more accurate intermediate scale solutions. However, due to the lack of consistent multi-dimensional numerical formulations in conventional schemes for triangular and tetrahedral meshes at the cell interfaces, numerical issues exist when flow discontinuities or stagnation regions are present. The space-time conservative conservation element solution element (CESE) method - due to its Riemann-solver-free shock capturing capabilities, non-dissipative baseline schemes, and flux conservation in time as well as space - has the potential to more accurately simulate turbulent flows using unstructured tetrahedral meshes. To pave the way towards accurate simulation of shock/turbulent boundary-layer interaction, a series of wave and shock interaction benchmark problems that increase in complexity, are computed in this paper with triangular/tetrahedral meshes. Preliminary computations for the normal shock/turbulence interactions are carried out with a relatively coarse mesh, by direct numerical simulations standards, in order to assess other effects such as boundary conditions and the necessity of a buffer domain. The results indicate that qualitative agreement with previous studies can be obtained for flows where, strong shocks co-exist along with unsteady waves that display a broad range of scales, with a relatively compact computational domain and less stringent requirements for grid clustering near the shock. With the space-time conservation properties, stable solutions without any spurious wave reflections can be obtained without a need for buffer domains near the outflow/farfield boundaries. Computational results for the

  19. Magnetic cellulose ionomer/layered double hydroxide: An efficient anion exchange platform with enhanced diclofenac adsorption property.

    PubMed

    Hossein Beyki, Mostafa; Mohammadirad, Mosleh; Shemirani, Farzaneh; Saboury, Ali Akbar

    2017-02-10

    Polymeric ionomers with anion exchange capability are considered to be classes of environmentally friendly compounds as combination of them with anionic layered hydroxides constitute emerging advance materials. Biosorption by polymeric ionomer - layered double hydroxide (LDH) hybrid material exhibits an attractive green, low cost and low toxic - clean way. As a result, a novel anion exchange platform has been developed by the reaction of CaAl - LDH with Fe(2+), cellulose solution, epichlorohydrin and pyridine. Magnetite cellulose - LDH (MCL) and the ionomer were used for efficient biosorption of diclofenac sodium (DF). Results showed that ionomer has more efficiency for DF adsorption relative to MCL. Magnetite ionomer showed fast equilibrium time (2min) with maximum uptake of 268mgg(-1). Isotherm and Kinetic models were also studied. Regeneration of the sorbent was performed with a mixture of methanol -NaOH (2.0molL(-1)) solution.

  20. The nature and evolution of excess electron binding in cluster anions studied via negative ion photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Hendricks, Jay H.

    1997-07-01

    The technique of negative ion photoelectron spectroscopy (NIPES) has been used to study a variety of cluster anion systems with the aim of elucidating the nature and evolution of excess electron binding in clusters. The systems studied include molecular and cluster dipole- bound anions, conventional valence molecular anions, ion- molecule cluster anions, solvated electron cluster anions, metal cluster anions, metal oxide anions, and metal hydride anions. The generation and characterization of nanophase Lunsford catalyst, and the study of gas- phase anionic polymerization reactions were also conducted. The studies of dipole-bound anions, (Uracil)/sp-, (Uracil...Xe)/sp-, (Thymine)/sp-, (1- Methylcytosine)/sp-, (HF)2-, (H2O)2-, (EG)2-, where EG = Ethylene Glycol, (CH3CN[/cdots]H2O)/sp-,/ (HCl[/cdots] H2O)/sp-,/ (HCN[/cdots]H2O)/sp-, and (H2S)4- provide some of the best experimental evidence to date confirming the long standing predictions of theory that an excess electron can be bound to a dipole field if the dipole moment of the neutral molecule or cluster exceeds a critical minimum value. The photodetachment of the conventional valence anions /[(2,4,6-tricyanobenzene)/sp-, (CAN3-3HCl)/sp-, where CAN = 2- choloracrylonitrile, (CH3NO2)/sp-/], metal cluster anions /[Lin=1-7-/], metal oxide anions /[NaO/sp-,/ KO/sp-,/ RbO/sp-, and CsO/sp-/] and metal hydride anions /[LiH/sp-,/ LiD/sp-/] enabled the first time determinations of vertical detachment energies, and adiabatic election affinities. The studies of ion-molecule cluster anions /[O/sp- (Ar)n=1-26,34,/ NO/sp-(Ar)n=1-14,/ O/sp- (Kr)n=1-4,/ O/sp-(Xe)n=1-4,/ O/sp-(N2),/ NO/sp-(Kr),/ NO/sp-(Xe)n=1-3,/ NO/sp- (N2O)n=1-5, and NO/sp-(EG),/ (Uracil[/cdots]H2O)/sp-,/ (Uracil[/cdots]Xe)/sp-/] permitted the energetics and structure of microscopic ion solvation to be examined as a function of cluster size and cluster solvent. The photodetachment of solvated the electron clusters anions /[(H2O)n-,/ [(H2O)x[/cdots](NH3)y

  1. Anion binding in biological systems

    NASA Astrophysics Data System (ADS)

    Feiters, Martin C.; Meyer-Klaucke, Wolfram; Kostenko, Alexander V.; Soldatov, Alexander V.; Leblanc, Catherine; Michel, Gurvan; Potin, Philippe; Küpper, Frithjof C.; Hollenstein, Kaspar; Locher, Kaspar P.; Bevers, Loes E.; Hagedoorn, Peter-Leon; Hagen, Wilfred R.

    2009-11-01

    We compare aspects of biological X-ray absorption spectroscopy (XAS) studies of cations and anions, and report on some examples of anion binding in biological systems. Brown algae such as Laminaria digitata (oarweed) are effective accumulators of I from seawater, with tissue concentrations exceeding 50 mM, and the vanadate-containing enzyme haloperoxidase is implicated in halide accumulation. We have studied the chemical state of iodine and its biological role in Laminaria at the I K edge, and bromoperoxidase from Ascophyllum nodosum (knotted wrack) at the Br K edge. Mo is essential for many forms of life; W only for certain archaea, such as Archaeoglobus fulgidus and the hyperthermophilic archaeon Pyrococcus furiosus, and some bacteria. The metals are bound and transported as their oxo-anions, molybdate and tungstate, which are similar in size. The transport protein WtpA from P. furiosus binds tungstate more strongly than molybdate, and is related in sequence to Archaeoglobus fulgidus ModA, of which a crystal structure is known. We have measured A. fulgidus ModA with tungstate at the W L3 (2p3/2) edge, and compared the results with the refined crystal structure. XAS studies of anion binding are feasible even if only weak interactions are present, are biologically relevant, and give new insights in the spectroscopy.

  2. OH3- and O2H5- double Rydberg anions: Predictions and comparisons with NH4- and N2H7-

    NASA Astrophysics Data System (ADS)

    Melin, Junia; Ortiz, J. V.

    2007-07-01

    A low barrier in the reaction pathway between the double Rydberg isomer of OH3- and a hydride-water complex indicates that the former species is more difficult to isolate and characterize through anion photoelectron spectroscopy than the well known double Rydberg anion (DRA), tetrahedral NH4-. Electron propagator calculations of vertical electron detachment energies (VEDEs) and isosurface plots of the electron localization function disclose that the transition state's electronic structure more closely resembles that of the DRA than that of the hydride-water complex. Possible stabilization of the OH3- DRA through hydrogen bonding or ion-dipole interactions is examined through calculations on O2H5- species. Three O2H5- minima with H-(H2O)2, hydrogen-bridged, and DRA-molecule structures resemble previously discovered N2H7- species and have well separated VEDEs that may be observable in anion photoelectron spectra.

  3. Bicontinuous Polymeric Microemulsions from Polydisperse Diblock Copolymers

    SciTech Connect

    Ellison, Christopher J.; Meuler, Adam J.; Qin, Jian; Evans, Christopher M.; Wolf, Lynn M.; Bates, Frank S.

    2009-06-12

    Polymeric bicontinuous microemulsions are thermodynamically stable structures typically formed by ternary blends of immiscible A and B homopolymers and a macromolecular surfactant such as an AB diblock copolymer. Investigations of these bicontinuous morphologies have largely focused on model systems in which all components have narrow molecular weight distributions. Here we probe the effects of AB diblock polydispersity in ternary blends of polystyrene (PS), polyisoprene (PI), and poly(styrene-b-isoprene) (PS-PI). Three series of blends were prepared using the same PS and PI homopolymers; two of them contain nearly monodisperse components while the third includes a polydisperse PS-PI diblock. The PS and PI homopolymers and two of the PS-PI diblocks were prepared by anionic polymerization using sec-butyllithium and have narrow molecular weight distributions. The polydisperse PS-PI diblock was prepared by anionic polymerization using the functional organolithium 3-tert-butyldimethylsilyloxy-1-propyllithium; this diblock has a polydisperse PS block (M{sub w}/M{sub n} = 1.57) and a nearly monodisperse PI block (Mw/Mn < 1.1). The phase behavior of the three series of blends was probed using a combination of dynamic mechanical spectroscopy, small-angle X-ray scattering, and cloud point measurements, and a bicontinuous microemulsion channel was identified in each system. These results prove that monodisperse components are not required to form bicontinuous microemulsions and highlight the utility of polydispersity as a tool to tune polymer blend phase behavior. The random-phase approximation, originally advanced by de Gennes, and self-consistent field theory are used to provide a theoretical supplement to the experimental work. These theories are able to predict the directions of the polydispersity-driven shifts in domain spacing, order-disorder transition temperatures, and the location of the microemulsion channel. Self-consistent field theory is also used in conjunction

  4. Bicontinuous polymeric microemulsions from polydisperse diblock copolymers.

    PubMed

    Ellison, Christopher J; Meuler, Adam J; Qin, Jian; Evans, Christopher M; Wolf, Lynn M; Bates, Frank S

    2009-03-26

    Polymeric bicontinuous microemulsions are thermodynamically stable structures typically formed by ternary blends of immiscible A and B homopolymers and a macromolecular surfactant such as an AB diblock copolymer. Investigations of these bicontinuous morphologies have largely focused on model systems in which all components have narrow molecular weight distributions. Here we probe the effects of AB diblock polydispersity in ternary blends of polystyrene (PS), polyisoprene (PI), and poly(styrene-b-isoprene) (PS-PI). Three series of blends were prepared using the same PS and PI homopolymers; two of them contain nearly monodisperse components while the third includes a polydisperse PS-PI diblock. The PS and PI homopolymers and two of the PS-PI diblocks were prepared by anionic polymerization using sec-butyllithium and have narrow molecular weight distributions. The polydisperse PS-PI diblock was prepared by anionic polymerization using the functional organolithium 3-tert-butyldimethylsilyloxy-1-propyllithium; this diblock has a polydisperse PS block (Mw/Mn = 1.57) and a nearly monodisperse PI block (Mw/Mn < 1.1). The phase behavior of the three series of blends was probed using a combination of dynamic mechanical spectroscopy, small-angle X-ray scattering, and cloud point measurements, and a bicontinuous microemulsion channel was identified in each system. These results prove that monodisperse components are not required to form bicontinuous microemulsions and highlight the utility of polydispersity as a tool to tune polymer blend phase behavior. The random-phase approximation, originally advanced by de Gennes, and self-consistent field theory are used to provide a theoretical supplement to the experimental work. These theories are able to predict the directions of the polydispersity-driven shifts in domain spacing, order-disorder transition temperatures, and the location of the microemulsion channel. Self-consistent field theory is also used in conjunction with the

  5. Gallium based low-interaction anions

    DOEpatents

    King, Wayne A.; Kubas, Gregory J.

    2000-01-01

    The present invention provides: a composition of the formula M.sup.+x (Ga(Y).sub.4.sup.-).sub.x where M is a metal selected from the group consisting of lithium, sodium, potassium, cesium, calcium, strontium, thallium, and silver, x is an integer selected from the group consisting of 1 or 2, each Y is a ligand selected from the group consisting of aryl, alkyl, hydride and halide with the proviso that at least one Y is a ligand selected from the group consisting of aryl, alkyl and halide; a composition of the formula (R).sub.x Q.sup.+ Ga(Y).sub.4.sup.- where Q is selected from the group consisting of carbon, nitrogen, sulfur, phosphorus and oxygen, each R is a ligand selected from the group consisting of alkyl, aryl, and hydrogen, x is an integer selected from the group consisting of 3 and 4 depending upon Q, and each Y is a ligand selected from the group consisting of aryl, alkyl, hydride and halide with the proviso that at least one Y is a ligand selected from the group consisting of aryl, alkyl and halide; an ionic polymerization catalyst composition including an active cationic portion and a gallium based weakly coordinating anion; and bridged anion species of the formula M.sup.+x.sub.y [X(Ga(Y.sub.3).sub.z ].sup.-y.sub.x where M is a metal selected from the group consisting of lithium, sodium, potassium, magnesium, cesium, calcium, strontium, thallium, and silver, x is an integer selected from the group consisting of 1 or 2, X is a bridging group between two gallium atoms, y is an integer selected from the group consisting 1 and 2, z is an integer of at least 2, each Y is a ligand selected from the group consisting of aryl, alkyl, hydride and halide with the proviso that at least one Y is a ligand selected from the group consisting of aryl, alkyl and halide.

  6. Polymeric ion conductors

    SciTech Connect

    Nagai, J.; Mizuhashi, M.; Kamimori, T.

    1990-12-31

    There are several requirements for (polymeric) ion conductors in electrochromic window applications: (1) they have high ionic conductivity (desirably, > 1 {times} 10{sup {minus}4} Scm{sup {minus}1}); (2) they have high chemical and electrochemical stabilities with respect to the wide usable potential window and thermal and UV stabilities; (3) they are transparent in a specific wavelength region, which is, however, dependent of applications; and (4) they have enough adhesiveness to the substrates and have acceptable mechanical properties. Many kinds of polymeric ionic conductors have since been reported and some of them were applied to electrochromic uses. In this chapter, electrochemical and physicochemical properties of these materials are reviewed. However, certain aspects such as crystallographic studies and conduction models in detail have been omitted, which are still controversial.

  7. Organometallic polymerization catalysts

    SciTech Connect

    Waymouth, R.M.

    1993-12-31

    Well-defined transition metal catalysts have resulted in exciting new opportunities in polymer synthesis. The stereochemistry of vinyl polymers can be rationally controlled with choice of the appropriate catalysts. Studies with optically active catalyst precursors have revealed considerable information on the absolute stereochemistry of olefin polymerization and have led to the synthesis of novel chiral polyolefins. The development of homogeneous olefin metathesis catalysts has also led to a variety of well-defined new polymer structures with controlled molecular weight and molecular weight distribution. Recent advances in understanding the mechanisms and stereochemistry of homogeneous transition metal catalyzed polymerization will be discussed. The ability to control polymer structure through catalyst design presents exciting opportunities in the synthesis of {open_quotes}tailor-made{close_quotes} macromolecules.

  8. Screening of anionic-modified polymers in terms of stability, disintegration, and swelling behavior.

    PubMed

    Laffleur, Flavia; Ijaz, Muhammad; Menzel, Claudia

    2017-11-01

    This study aimed to screen the stability, disintegration, and swelling behavior of chemically modified anionic polymers. Investigated polymers were well-known and widely used staples of the pharmaceutical and medical field, namely, alginate (AL), carboxymethyl cellulose (CMC), polycarbophil (PC), and hyaluronic acid (HA). On the basis of amide bond formation between the carboxylic acid moieties of anionic polymers and the primary amino group of the modification ligand cysteine (CYS), the modified polymers were obtained. Unmodified polymers served as controls throughout all studies. With the Ellman's assay, modification degrees were determined of synthesized polymeric excipients. Stability assay in terms of erosion study at physiological conditions were performed. Moreover, water uptake of compressed polymeric discs were evaluated and further disintegration studies according to the USP were carried out to define the potential ranking. Results ranking figured out PCCYS > CMCCYS > HACYS > ALCYS in terms of water uptake capacity compared to respective controls. Cell viability assays on Caco-2 cell line as well as on RPMI 2650 (ATTC CCL30) proved modification not being harmful to those. Due to the results of this study, an intense screening of prominent anionic polymer derivate was performed in order to help the pharmaceutical research for the best choice of polymeric excipients for developments of controlled drug release systems.

  9. Artificial intelligence approach to planning the robotic assembly of large tetrahedral truss structures

    NASA Technical Reports Server (NTRS)

    Homemdemello, Luiz S.

    1992-01-01

    An assembly planner for tetrahedral truss structures is presented. To overcome the difficulties due to the large number of parts, the planner exploits the simplicity and uniformity of the shapes of the parts and the regularity of their interconnection. The planning automation is based on the computational formalism known as production system. The global data base consists of a hexagonal grid representation of the truss structure. This representation captures the regularity of tetrahedral truss structures and their multiple hierarchies. It maps into quadratic grids and can be implemented in a computer by using a two-dimensional array data structure. By maintaining the multiple hierarchies explicitly in the model, the choice of a particular hierarchy is only made when needed, thus allowing a more informed decision. Furthermore, testing the preconditions of the production rules is simple because the patterned way in which the struts are interconnected is incorporated into the topology of the hexagonal grid. A directed graph representation of assembly sequences allows the use of both graph search and backtracking control strategies.

  10. A Reconstructed Discontinuous Galerkin Method for the Compressible Flows on Unstructured Tetrahedral Grids

    SciTech Connect

    Hong Luo; Yidong Xia; Robert Nourgaliev; Chunpei Cai

    2011-06-01

    A reconstruction-based discontinuous Galerkin (RDG) method is presented for the solution of the compressible Navier-Stokes equations on unstructured tetrahedral grids. The RDG method, originally developed for the compressible Euler equations, is extended to discretize viscous and heat fluxes in the Navier-Stokes equations using a so-called inter-cell reconstruction, where a smooth solution is locally reconstructed using a least-squares method from the underlying discontinuous DG solution. Similar to the recovery-based DG (rDG) methods, this reconstructed DG method eliminates the introduction of ad hoc penalty or coupling terms commonly found in traditional DG methods. Unlike rDG methods, this RDG method does not need to judiciously choose a proper form of a recovered polynomial, thus is simple, flexible, and robust, and can be used on unstructured grids. The preliminary results indicate that this RDG method is stable on unstructured tetrahedral grids, and provides a viable and attractive alternative for the discretization of the viscous and heat fluxes in the Navier-Stokes equations.

  11. Identifying Vortex-Core-Line using a tetrahedral satellite configuration: Field Topology Approach

    NASA Astrophysics Data System (ADS)

    Jiang, Yao; Lembege, Bertrand; Nishikawa, Ken-ichi; Cai, DongSheng; Hasegawa, Hiroshi

    2016-04-01

    Identifying vortices are the key to understanding the turbulence in plasma shear layers. Here, the term 'vortex' or 'vortex core' is associated with a region of Galilean invariance [Jeong and Hussain, 1995]. Unfortunately, no single precise definition of a vortex is currently universally accepted, despite the fact that many space plasma authors claim that many observations have detected "vortices" (as Kelvin-Helmholtz vortices at/around the magnetopause). By using the four satellite velocity data, and Taylor series, we expand the velocity data around the satellites, calculate its first order tensor, and linearly approximate the field. We can identify the vortex structures by using various vortex identification criteria as follows: (i) The first criterion is Q-criterion that defines vortices as regions in which the vorticity energy prevails other energies; (ii) the second criterion is the lambda2-criterion that is related to the minus of the Hessian matrix of the pressure related term; and (iii) the third criterion requires the existence of vortex-core-lines that is the Galilean invariance inside the four satellite tetrahedral region. Using these methods, we can identify and analyze more precisely the 3D vortex using tetrahedral satellite configuration.

  12. Octahedral versus tetrahedral coordination of Al in synthetic micas determined by XANES

    SciTech Connect

    Mottana, A.; Ventura, G.D.; Robert, J.L.

    1997-05-01

    We used the JUMBO monochromator at SSRL to measure the Al K-edge X-ray absorption spectra of synthetic micas having variable Al content and occupancy, from 0 to 2/3 in the octahedral M positions, and 0 to 2/3 in the tetrahedral T positions. The measured Al K edges differ markedly, but the differences may have a common explanation: (1) Micas containing 1/3 Al in M or {1/4} Al in T have K edges that differ in the energy and intensity of the first two features, which are related to interaction of Al with its first-shell nearest neighbors (O and OH or F). They are nearly identical to the K edges of reference minerals such as albite (tetrahedral Al only) or grossular (octahedral Al only). (2) Micas containing Al in both M and T have K edges that can be interpreted as a weighed combination of the simple edges. 39 refs., 4 figs., 1 tab.

  13. Structure and mechanical properties of low stress tetrahedral amorphous carbon films prepared by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Bonelli, M.; Ferrari, A. C.; Fioravanti, A.; Li Bassi, A.; Miotello, A.; Ossi, P. M.

    2002-02-01

    Tetrahedral amorphous carbon films have been produced by pulsed laser deposition, at a wavelength of 248 nm, ablating highly oriented pyrolytic graphite at room temperature, in a 10-2 Pa vacuum, at fluences ranging between 0.5 and 35 Jcm-2. Both (100) Si wafers and wafers covered with a SiC polycrystalline interlayer were used as substrates. Film structure was investigated by Raman spectroscopy at different excitation wavelength from 633 nm to 229 nm and by transmission Electron Energy Loss Spectroscopy. The films, which are hydrogen-free, as shown by Fourier Transform Infrared Spectroscopy, undergo a transition from mainly disordered graphitic to up to 80% tetrahedral amorphous carbon (ta-C) above a threshold laser fluence of 5 J cm-2. By X-ray reflectivity roughness, density and cross-sectional layering of selected samples were studied. Film hardness as high as 70 GPa was obtained by nanoindentation on films deposited with the SiC interlayer. By scratch test film adhesion and friction coefficients between 0.06 and 0.11 were measured. By profilometry we obtained residual stress values not higher than 2 GPa in as-deposited 80% sp3 ta-C films.

  14. Tetrahedral collapse: a rotational toy model of simultaneous dark-matter halo, filament and wall formation

    NASA Astrophysics Data System (ADS)

    Neyrinck, Mark C.

    2016-07-01

    We discuss an idealized model of halo formation, in which a collapsing halo node is tetrahedral, with a filament extruding from each of its four faces, and with a wall connecting each pair of filaments. In the model, filaments generally spin when they form, and the halo spins if and only if there is some rotation in filaments. This is the simplest possible fully three-dimensional halo collapse in the `origami approximation', in which voids are irrotational, and the dark-matter sheet out of which dark-matter structures form is allowed to fold in position-velocity phase space, but not stretch (i.e. it cannot vary in density along a stream). Up to an overall scaling, the four filament directions, and only three other quantities, such as filament spins, suffice to determine all of the collapse's properties: the shape, mass, and spin of the halo; the densities per unit length and spins of all filaments; and masses per unit area of the walls. If the filaments are arranged regular-tetrahedrally, filament properties obey simple laws, reminiscent of angular-momentum conservation. The model may be most useful in understanding spin correlations between neighbouring galaxies joined by filaments; these correlations would give intrinsic alignments between galaxies, essential to understand for accurate cosmological weak-lensing measurements.

  15. Maintaining tetrahedral mesh quality in response to time-dependent topological and geometrical deformation

    SciTech Connect

    Kuprat, A.; George, D.

    1998-12-01

    When modeling deformation of geometrically complex regions, unstructured tetrahedral meshes provide the flexibility necessary to track interfaces as they change geometrically and topologically. In the class of time-dependent simulations considered in this paper, multimaterial interfaces are represented by sets of triangular facets, and motion of the interfaces is controlled by physical considerations. The motion of interior points in the conforming tetrahedral mesh (i.e., points not on interfaces) is arbitrary and may be chosen to produce good element shapes. In the context of specified boundary motion driven by physical considerations, they have found that a rather large glossary of mesh changes is required to allow the simulation to survive all the transitions of interface geometry and topology that occur during time evolution. This paper will describe mesh changes required to maintain good element quality as the geometry evolves, as well as mesh changes required to capture changes i n topology that occur when material regions collapse or pinch off. This paper will present a detailed description of mesh changes necessary for capturing the aforementioned geometrical and topological changes, as implemented in the code GRAIN3D, and will provide examples from a metallic grain growth simulation in which the normal velocity of the grain boundary is proportional to mean curvature.

  16. Polymeric Microcapsule Arrays.

    DTIC Science & Technology

    1995-03-24

    support, microencapsulation and entrapment within a membrane/film or gel. The ideal enzyme immobilization method would (1) Employ mild chemical...yields hollow polymeric microcapsules of uniform diameter and length. These microcapsules are arranged in a high density array in which the...individual capsules protrude from a surface like the bristles of a brush. We have developed procedures for filling these microcapsules with high

  17. Frontal Polymerization in Microgravity

    NASA Technical Reports Server (NTRS)

    Pojman, John A.

    1999-01-01

    Frontal polymerization systems, with their inherent large thermal and compositional gradients, are greatly affected by buoyancy-driven convection. Sounding rocket experiments allowed the preparation of benchmark materials and demonstrated that methods to suppress the Rayleigh-Taylor instability in ground-based research did not significantly affect the molecular weight of the polymer. Experiments under weightlessness show clearly that bubbles produced during the reaction interact very differently than under 1 g.

  18. The Anion Effect on Li(+) Ion Coordination Structure in Ethylene Carbonate Solutions.

    PubMed

    Jiang, Bo; Ponnuchamy, Veerapandian; Shen, Yuneng; Yang, Xueming; Yuan, Kaijun; Vetere, Valentina; Mossa, Stefano; Skarmoutsos, Ioannis; Zhang, Yufan; Zheng, Junrong

    2016-09-15

    Rechargeable lithium ion batteries are an attractive alternative power source for a wide variety of applications. To optimize their performances, a complete description of the solvation properties of the ion in the electrolyte is crucial. A comprehensive understanding at the nanoscale of the solvation structure of lithium ions in nonaqueous carbonate electrolytes is, however, still unclear. We have measured by femtosecond vibrational spectroscopy the orientational correlation time of the CO stretching mode of Li(+)-bound and Li(+)-unbound ethylene carbonate molecules, in LiBF4, LiPF6, and LiClO4 ethylene carbonate solutions with different concentrations. Surprisingly, we have found that the coordination number of ethylene carbonate in the first solvation shell of Li(+) is only two, in all solutions with concentrations higher than 0.5 M. Density functional theory calculations indicate that the presence of anions in the first coordination shell modifies the generally accepted tetrahedral structure of the complex, allowing only two EC molecules to coordinate to Li(+) directly. Our results demonstrate for the first time, to the best of our knowledge, the anion influence on the overall structure of the first solvation shell of the Li(+) ion. The formation of such a cation/solvent/anion complex provides a rational explanation for the ionic conductivity drop of lithium/carbonate electrolyte solutions at high concentrations.

  19. Developments in polymerization lamps.

    PubMed

    Jiménez-Planas, Amparo; Martín, Juan; Abalos, Camilo; Llamas, Rafael

    2008-02-01

    Polymerization shrinkage of composite resins and the consequent stress generated at the composite-tooth interface continue to pose a serious clinical challenge. The development of high-intensity halogen lamps and the advent of curing units providing higher energy performance, such as laser lamps, plasma arc units, and, most recently, light-emitting diode (LED) curing units, have revolutionized polymerization lamp use and brought major changes in light-application techniques. A comprehensive review of the literature yielded the following conclusions: (1) the most reliable curing unit for any type of composite resin is the high-density halogen lamp, fitted with a programming device to enable both pulse-delay and soft-start techniques; (2) if any other type of curing unit is used, information must be available on the compatibility of the unit with the composite materials to be used; (3) polymerization lamp manufacturers need to focus on the ongoing development of LED technology; (4) further research is required to identify the most reliable light-application techniques.

  20. Ion exchange polymers for anion separations

    DOEpatents

    Jarvinen, Gordon D.; Marsh, S. Fredric; Bartsch, Richard A.

    1997-01-01

    Anion exchange resins including at least two positively charged sites and a ell-defined spacing between the positive sites are provided together with a process of removing anions or anionic metal complexes from aqueous solutions by use of such resins. The resins can be substituted poly(vinylpyridine) and substituted polystyrene.

  1. Ion exchange polymers for anion separations

    DOEpatents

    Jarvinen, G.D.; Marsh, S.F.; Bartsch, R.A.

    1997-09-23

    Anion exchange resins including at least two positively charged sites and a well-defined spacing between the positive sites are provided together with a process of removing anions or anionic metal complexes from aqueous solutions by use of such resins. The resins can be substituted poly(vinylpyridine) and substituted polystyrene.

  2. Binding Hydrated Anions with Hydrophobic Pockets.

    PubMed

    Sokkalingam, Punidha; Shraberg, Joshua; Rick, Steven W; Gibb, Bruce C

    2016-01-13

    Using a combination of isothermal titration calorimetry and quantum and molecular dynamics calculations, we demonstrate that relatively soft anions have an affinity for hydrophobic concavity. The results are consistent with the anions remaining partially hydrated upon binding, and suggest a novel strategy for anion recognition.

  3. Polymerization and photochromism of ammonium molybdate in porous glass

    NASA Astrophysics Data System (ADS)

    Pak, V. N.; Borisov, A. N.

    2016-08-01

    Modification of porous glass (PG) plates is carried out by impregnation with aqueous solutions of ammonium molybdate (NH4)2MoO4 with subsequent removal of water at 120°C. A long-wavelength shift of absorption spectra upon accumulation of the salt in PG indicates polymerization of MoO 4 2- anions at low concentrations of the encapsulated salt. Photochromism manifests itself as the anionic forms in PG become larger. UV irradiation of the modified plates causes enhancement of continuous absorption in the visible range. The proposed mechanism of photoreduction of the polianions in PG involves the removal of oxygen atoms from the bridging-Mo-O-Mo-bonds and stabilization of the colored forms by means of conjugation of the electrons released from the 4 d-levels of pentavalent molybdenum.

  4. Introduction of Living Polymerization. Living and/or Controlled Polymerization

    DTIC Science & Technology

    1994-06-30

    separated into kinetic and synthetic. The intention of this paper is not to review existing and proclaimed living systems but to discuss the essence of a...o1 OFFICE OF NAVAL RESEARCH S4 CONTRACT N00014-94-1-0101 I R&T Code 31321075 Technical Report No. 10 INTRODUCTION TO LIVING POLYMERIZATION. LIVING ...TITLE AND SUBTITLE S. FUNDING NUMBERS Introduction to Living Polymerization. Living and/or Controlled Polymerization N00014-94-1-0101 6. AUTHOR(S

  5. Geometrical and algebraic approach to central molecular chirality: a chirality index and an Aufbau description of tetrahedral molecules.

    PubMed

    Capozziello, Salvatore; Lattanzi, Alessandra

    2006-08-01

    On the basis of empirical Fischer projections, we develop an algebraic approach to the central molecular chirality of tetrahedral molecules. The elements of such an algebra are obtained from the 24 projections which a single chiral tetrahedron can generate in S and R absolute configurations. They constitute a matrix representation of the O4 orthogonal group. According to this representation, given a molecule with n chiral centres, it is possible to define an "index of chirality chi identical with {n, p}", where n is the number of stereogenic centres of the molecule and p the number of permutations observed under rotations and superimpositions of the tetrahedral molecule to its mirror image. The chirality index not only assigns the global chirality of a given tetrahedral chain, but indicates also a way to predict the same property for new compounds, which can be built up consistently.

  6. Molecular cloning, nucleotide sequence, and abscisic acid induction of a suberization-associated highly anionic peroxidase.

    PubMed

    Roberts, E; Kolattukudy, P E

    1989-06-01

    A highly anionic peroxidase induced in suberizing cells was suggested to be the key enzyme involved in polymerization of phenolic monomers to generate the aromatic matrix of suberin. The enzyme encoded by a potato cDNA was found to be highly homologous to the anionic peroxidase induced in suberizing tomato fruit. A tomato genomic library was screened using the potato anionic peroxidase cDNA and one genomic clone was isolated that contained two tandemly oriented anionic peroxidase genes. These genes were sequenced and were 96% and 87% identical to the mRNA for potato anionic peroxidase. Both genes consist of three exons with the relative positions of their two introns being conserved between the two genes. Primer extension analysis showed that only one of the genes is expressed in the periderm of 3 day wound-healed tomato fruits. Southern blot analyses suggested that there are two copies each of the two highly homologous genes per haploid genome in both potato and tomato. Abscisic acid (ABA) induced the accumulation of the anionic peroxidase transcripts in potato and tomato callus tissues. Northern blots showed that peroxidase mRNA was detectable at 2 days and was maximal at 8 days after transfer of potato callus to solid agar media containing 10(-4) M ABA. The transcripts induced by ABA in both potato and tomato callus were identical in size to those induced in wound-healing potato tuber and tomato fruit. The anionic peroxidase peptide was detected in extracts of potato callus grown on the ABA-containing media by western blot analysis. The results support the suggestion that stimulation of suberization by ABA involves the induction of the highly anionic peroxidase.

  7. Modeling anion adsorption on kaolinite

    SciTech Connect

    Weerasooriya, R.; Wickramarathna, H.U.S.

    1999-05-15

    Anion adsorption onto kaolinite was quantified using the triple layer surface complexation model. Fluoride adsorption data were described by both anion exchange and H-bonded complexation mechanisms. The outer-sphere complexation mechanism was used to describe the weak adsorption of Cl{sup {minus}}, Br{sup {minus}}, and I{sup {minus}} on kaolinite. The F{sup {minus}} adsorption in the presence of Br{sup {minus}} or I{sup {minus}} was decreased over a range of pH 4--5 whereas Cl{sup {minus}} showed a negligible effect. Competition for binding sites appeared to be an important factor in determining the adsorptive behavior of F{sup {minus}} in Br{sup {minus}} or I{sup {minus}} mediated systems.

  8. Anion Solvation in Carbonate Electrolytes

    SciTech Connect

    Zhang, Zhengcheng

    2015-11-16

    With the correlation between Li+ solvation and interphasial chemistry on anodes firmly established in Li-ion batteries, the effect of cation–solvent interaction has gone beyond bulk thermodynamic and transport properties and become an essential element that determines the reversibility of electrochemistry and kinetics of Li-ion intercalation chemistries. As of now, most studies are dedicated to the solvation of Li+, and the solvation of anions in carbonate-based electrolytes and its possible effect on the electrochemical stability of such electrolytes remains little understood. As a mirror effort to prior Li+ solvation studies, this work focuses on the interactions between carbonate-based solvents and two anions (hexafluorophosphate, PF6–, and tetrafluoroborate, BF4–) that are most frequently used in Li-ion batteries. The possible correlation between such interaction and the interphasial chemistry on cathode surface is also explored.

  9. Laser cooling of molecular anions.

    PubMed

    Yzombard, Pauline; Hamamda, Mehdi; Gerber, Sebastian; Doser, Michael; Comparat, Daniel

    2015-05-29

    We propose a scheme for laser cooling of negatively charged molecules. We briefly summarize the requirements for such laser cooling and we identify a number of potential candidates. A detailed computation study with C_{2}^{-}, the most studied molecular anion, is carried out. Simulations of 3D laser cooling in a gas phase show that this molecule could be cooled down to below 1 mK in only a few tens of milliseconds, using standard lasers. Sisyphus cooling, where no photodetachment process is present, as well as Doppler laser cooling of trapped C_{2}^{-}, are also simulated. This cooling scheme has an impact on the study of cold molecules, molecular anions, charged particle sources, and antimatter physics.

  10. Aza compounds as anion receptors

    DOEpatents

    Lee, Hung Sui; Yang, Xiao-Qing; McBreen, James

    1998-01-06

    A family of aza-ether based compounds including linear, multi-branched and aza-crown ethers is provided. When added to non-aqueous battery electrolytes, the family of aza-ether based compounds acts as neutral receptors to complex the anion moiety of the electrolyte salt thereby increasing the conductivity and the transference number of Li.sup.+ ion in alkali metal batteries.

  11. Aza compounds as anion receptors

    DOEpatents

    Lee, H.S.; Yang, X.Q.; McBreen, J.

    1998-01-06

    A family of aza-ether based compounds including linear, multi-branched and aza-crown ethers is provided. When added to non-aqueous battery electrolytes, the family of aza-ether based compounds acts as neutral receptors to complex the anion moiety of the electrolyte salt thereby increasing the conductivity and the transference number of Li{sup +} ion in alkali metal batteries. 3 figs.

  12. Ionol (BHT) produces superoxide anion.

    PubMed

    Smirnova, E G; Lyubimov, Yu I; Malinina, T G; Lyubimova, E Yu; Alexandrushkina, N I; Vanyushin, B F; Kolesova, G M; Yaguzhinsky, L S

    2002-11-01

    In aqueous medium etiolated wheat seedlings release superoxide anion (O2*-). Interaction of a synthetic antioxidant, butylated hydroxytoluene (BHT, ionol), with oxygen in the aqueous medium is accompanied by O2*- formation. This suggests that under certain conditions BHT behaves as a prooxidant. A natural antioxidant, superoxide dismutase (SOD), and also a wound healing preparation, emulsified denatured placenta (EDP), do not exhibit the prooxidant properties. In contrast to BHT, they reduce O2*- production by the etiolated wheat seedling system.

  13. Anion-Anion Bonding and Topology in Ternary Iridium Seleno-Stannides.

    PubMed

    Trump, Benjamin A; Tutmaher, Jake A; McQueen, Tyrel M

    2015-12-21

    The synthesis and physical properties of two new and one known Ir-Sn-Se compound are reported. Their crystal structures are elucidated with transmission electron microscopy and powder X-ray diffraction. IrSn0.45Se1.55 is a pyrite phase which consists of tilted corner-sharing IrX6 octahedra with randomly distributed (Sn-Se)(4-) and (Se-Se)(2-) dimers. Ir2Sn3Se3 is a known trigonally distorted skutterudite that consists of cooperatively tilted corner-sharing IrSn3Se3 octahedra with ordered (Sn-Se)2(4-) tetramers. Ir2SnSe5 is a layered, distorted β-MnO2 (pyrolusite) structure consisting of a double IrSe6 octrahedral row, corner sharing in the a direction and edge sharing in the b direction. This distorted pyrolusite contains (Se-Se)(2-) dimers and Se(2-) anions, and each double row is "capped" with a (Sn-Se)n polymeric chain. Resistivity, specific heat, and magnetization measurements show that all three have insulating and diamagnetic behavior, indicative of low-spin 5d(6) Ir(3+). Electronic structure calculations on Ir2Sn3Se3 show a single, spherical, nonspin-orbit split valence band and suggest that Ir2Sn3Se3 is topologically nontrivial under tensile strain due to inversion of Ir-d and Se-p states.

  14. Sol-gel chemistry by ring-opening polymerization

    SciTech Connect

    RAHIMIAN,KAMYAR; LOY,DOUGLAS A.

    2000-02-07

    Sol-gel processing of materials is plagued by shrinkage during polymerization of the alkoxide monomers and processing (aging and drying) of the resulting gels. The authors have developed a new class of hybrid organic-inorganic materials based on the solventless ring-opening polymerization (ROP) of monomers bearing the 2,2,5,5-tetramethyl-2,5-disilaoxacyclopentyl group, which permits them to drastically reduce shrinkage in sol-gel processed materials. Because the monomers are polymerized through a chain growth mechanism catalyzed by base rather than the step growth mechanism normally used in sol-gel systems, hydrolysis and condensation products are entirely eliminated. Furthermore, since water is not required for hydrolysis, an alcohol solvent is not necessary. Monomers with two disilaoxacyclopentyl groups, separated by a rigid phenylene group or a more flexible alkylene group, were prepared through disilylation of the corresponding diacetylenes, followed by ring closure and hydrogenation. Anionic polymerization of these materials, either neat or with 2,2,5,5-tetramethyl-2,5-disila-1-oxacyclopentane as a copolymer, affords thermally stable transparent gels with no visible shrinkage. These materials provide an easy route to the introduction of sol-gel type materials in encapsulation of microelectronics, which they have successfully demonstrated.

  15. Hosting anions. The energetic perspective.

    PubMed

    Schmidtchen, Franz P

    2010-10-01

    Hosting anions addresses the widely spread molecular recognition event of negatively charged species by dedicated organic compounds in condensed phases at equilibrium. The experimentally accessible energetic features comprise the entire system including the solvent, any buffers, background electrolytes or other components introduced for e.g. analysis. The deconvolution of all these interaction types and their dependence on subtle structural variation is required to arrive at a structure-energy correlation that may serve as a guide in receptor construction. The focus on direct host-guest interactions (lock-and-key complementarity) that have dominated the binding concepts of artificial receptors in the past must be widened in order to account for entropic contributions which constitute very significant fractions of the total free energy of interaction. Including entropy necessarily addresses the ambiguity and fuzziness of the host-guest structural ensemble and requires the appreciation of the fact that most liquid phases possess distinct structures of their own. Apparently, it is the perturbation of the intrinsic solvent structure occurring upon association that rules ion binding in polar media where ions are soluble and abundant. Rather than specifying peculiar structural elements useful in anion binding this critical review attempts an illumination of the concepts and individual energetic contributions resulting in the final observation of specific anion recognition (95 references).

  16. Molecular orbital (MSXα) calculations of s-electron densities of tetrahedrally coordinated ferric iron: Comparison with experimental isomer shifts

    NASA Astrophysics Data System (ADS)

    Tang Kai, A.; Annersten, H.; Ericsson, T.

    1980-04-01

    The MSXα method has been used to calculate the s-electron densities at the nucleus for tetrahedrally coordinated ferric iron, (FeO4)5-, comparing the observed increase in isomer shift values with increasing Fe-O separation. The results give an isomer shift calibration constant of -0.3 (a.u. mm×s-1) assuming a constant ratio for the iron and oxygen sphere radii for the different polyhedra sizes. It is suggested that increasing bonding distances in tetrahedral coordination polyhedra are the dominant factors determining the value of the isomer shifts in Fe-Mg-silicates.

  17. Cryoprotective properties of completely synthetic polyampholytes via reversible addition-fragmentation chain transfer (RAFT) polymerization and the effects of hydrophobicity.

    PubMed

    Rajan, Robin; Jain, Minkle; Matsumura, Kazuaki

    2013-01-01

    A completely synthetic polyampholyte cryoprotectant was developed with cationic and anionic monomers by reversible addition-fragmentation chain transfer polymerization. The neutralized random polyampholyte, which had an equal composition ratio of monomers, showed high cryoprotective properties in mammalian cells. Introduction of a small amount of hydrophobic monomer enhanced cell viability after cryopreservation, indicating the importance of hydrophobicity. Leakage experiments confirmed that these polyampholytes protected the cell membrane during cryopreservation. Due to low cytotoxicity, this polyampholyte has the potential to replace the convention cryoprotective agent dimethyl sulfoxide. The present study is the first to show that we can design a polymeric cryoprotectant that will protect the cell membrane during freezing using appropriate polymerization techniques.

  18. Hafnocene-Based Olefin Polymerizations

    NASA Astrophysics Data System (ADS)

    Diesner, T.; Troll, C.; Rieger, B.

    Zirconocenes have been used for a long time in the field of olefin polymerization using MAO as cocatalyst. The equivalent hafnocenes were seldom used due to a lack of productivity while using MAO activation. In the last few years borane and borate activation has come into the focus of research for olefin polymerization. A variety of different hafnocenes were used to investigate the polymerization mechanism and the different cocatalysts.

  19. Bimorphic polymeric photomechanical actuator

    NASA Technical Reports Server (NTRS)

    Sarkisov, Sergey S. (Inventor); Curley, Michael J. (Inventor); Adamovsky, Grigory (Inventor); Sarkisov, Jr., Sergey S. (Inventor); Fields, Aisha B. (Inventor)

    2006-01-01

    A bimorphic polymeric photomechanical actuator, in one embodiment using polyvinylidene fluoride (PVDF) as a photosensitive body, transmitting light over fiber optic cables, and controlling the shape and pulse duration of the light pulse to control movement of the actuator. Multiple light beams are utilized to generate different ranges of motion for the actuator from a single photomechanical body and alternative designs use multiple light beams and multiple photomechanical bodies to provide controlled movement. Actuator movement using one or more ranges of motion is utilized to control motion to position an actuating element in three dimensional space.

  20. Sustainable polymerizations in recoverable microemulsions.

    PubMed

    Chen, Zhenzhen; Yan, Feng; Qiu, Lihua; Lu, Jianmei; Zhou, Yinxia; Chen, Jiaxin; Tang, Yishan; Texter, John

    2010-03-16

    Free radical and atom-transfer radical polymerizations were conducted in monomer/ionic liquid microemulsions. After the polymerization and isolation of the resultant polymers, the mixture of the catalyst and ionic liquids (surfactant and continuous phase) can be recovered and reused, thereby dramatically improving the environmental sustainability of such chemical processing. The addition of monomer to recovered ionic liquid mixtures regenerates transparent, stable microemulsions that are ready for the next polymerization cycle upon addition of initiator. The method combines the advantages of IL recycling and microemulsion polymerization and minimizes environmental disposable effects from surfactants and heavy metal ions.

  1. Polymerization Evaluation by Spectrophotometric Measurements.

    ERIC Educational Resources Information Center

    Dunach, Jaume

    1985-01-01

    Discusses polymerization evaluation by spectrophotometric measurements by considering: (1) association degrees and molar absorptivities; (2) association degrees and equilibrium constants; and (3) absorbance and equilibrium constants. (JN)

  2. Anion-directed assemblies of cationic metal-organic frameworks based on 4,4'-bis(1,2,4-triazole): syntheses, structures, luminescent and anion exchange properties.

    PubMed

    Li, Xinxiong; Gong, Yaqiong; Zhao, Huaixia; Wang, Ruihu

    2014-11-17

    Three cationic metal-organic frameworks (MOFs), Ag(btr)·PF6·0.5CH3CN (1), Ag2(btr)2(H2O)·2CF3SO3·H2O (2), and Ag2(btr)2(NO3)·NO3 (3), were prepared from reaction of 4,4'-bis(1,2,4-triazole) (btr) with silver salts containing different anions. Complex 1 is a three-dimensional (3-D) framework constructed from tetrahedral-shaped nanoscale coordination cages with PF6(-) as counteranions. 2 and 3 are 3-D architectures containing 1-D channels, in which charge-balancing CF3SO3(-) and NO3(-) are located in their respective channels. Luminescent emission of 1-3 shows an obvious red shift compared with the btr ligand. Anion exchange studies show that 1 is able to selectively exchange MnO4(-) in aqueous solution with a modest capacity of 0.56 mol mol(-1); the luminescent emission of 1 is quickly quenched upon MnO4(-) exchange.

  3. From anion receptors to transporters.

    PubMed

    Gale, Philip A

    2011-03-15

    Cystic fibrosis is the most well-known of a variety of diseases termed channelopathies, in which the regulation of ion transport across cell membranes is so disrupted that the threshold of a pathology is passed. The human toll exacted by these diseases has led a number of research groups, including our own, to create compounds that mediate ion transport across lipid bilayers. In this Account, we discuss three classes of synthetic compounds that were refined to bind and transport anions across lipid bilayer membranes. All of the compounds were originally designed as anion receptors, that is, species that would simply create stable complexes with anions, but were then further developed as transporters. By studying structurally simple systems and varying their properties to change the degree of preorganization, the affinity for anions, or the lipophilicity, we have begun to rationalize why particular anion transport mechanisms (cotransport or antiport processes) occur in particular cases. For example, we have studied the chloride transport properties of receptors based on the closely related structures of isophthalamide and pyridine-2,6-dicarboxamide: the central ring in each case was augmented with pendant methylimidazole groups designed to cotransport H(+) and Cl(-). We observed that the more preorganized pyridine-based receptor was the more efficient transporter, a finding replicated with a series of isophthalamides in which one contained hydroxyl groups designed to preorganize the receptor. This latter class of compound, together with the natural product prodigiosin, can transport bicarbonate (as part of a chloride/bicarbonate antiport process) across lipid bilayer membranes. We have also studied the membrane transport properties of calix[4]pyrroles. Although the parent meso-octamethylcalix[4]pyrrole functions solely as a Cs(+)/Cl(-) cotransporter, other compounds with increased anion affinities can function through an antiport process. One example is octafluoro

  4. An assessment of the adaptive unstructured tetrahedral grid, Euler Flow Solver Code FELISA

    NASA Technical Reports Server (NTRS)

    Djomehri, M. Jahed; Erickson, Larry L.

    1994-01-01

    A three-dimensional solution-adaptive Euler flow solver for unstructured tetrahedral meshes is assessed, and the accuracy and efficiency of the method for predicting sonic boom pressure signatures about simple generic models are demonstrated. Comparison of computational and wind tunnel data and enhancement of numerical solutions by means of grid adaptivity are discussed. The mesh generation is based on the advancing front technique. The FELISA code consists of two solvers, the Taylor-Galerkin and the Runge-Kutta-Galerkin schemes, both of which are spacially discretized by the usual Galerkin weighted residual finite-element methods but with different explicit time-marching schemes to steady state. The solution-adaptive grid procedure is based on either remeshing or mesh refinement techniques. An alternative geometry adaptive procedure is also incorporated.

  5. Epitaxially stabilized iridium spinel oxide without cations in the tetrahedral site

    NASA Astrophysics Data System (ADS)

    Kuriyama, Hiromichi; Matsuno, Jobu; Niitaka, Seiji; Uchida, Masaya; Hashizume, Daisuke; Nakao, Aiko; Sugimoto, Kunihisa; Ohsumi, Hiroyuki; Takata, Masaki; Takagi, Hidenori

    2010-05-01

    Single-crystalline thin film of an iridium dioxide polymorph Ir2O4 has been fabricated by the pulsed laser deposition of LixIr2O4 precursor and the subsequent Li-deintercalation using soft chemistry. Ir2O4 crystallizes in a spinel (AB2O4) without A cations in the tetrahedral site, which is isostructural to λ-MnO2. Ir ions form a pyrochlore sublattice, which is known to give rise to a strong geometrical frustration. This Ir spinel was found to be a narrow gap insulator, in remarkable contrast to the metallic ground state of rutile-type IrO2. We argue that an interplay of a strong spin-orbit coupling and a Coulomb repulsion gives rise to an insulating ground state as in a layered perovskite Sr2IrO4.

  6. Self-assembly of a tetrahedral 58-nuclear barium vanadium oxide cluster.

    PubMed

    Kastner, Katharina; Puscher, Bianka; Streb, Carsten

    2013-01-07

    We report the synthesis and characterization of a molecular barium vanadium oxide cluster featuring high nuclearity and high symmetry. The tetrameric, 2.3 nm cluster H(5)[Ba(10)(NMP)(14)(H(2)O)(8)[V(12)O(33)](4)Br] is based on a bromide-centred, octahedral barium scaffold which is capped by four previously unknown [V(12)O(33)](6-) clusters in a tetrahedral fashion. The compound represents the largest polyoxovanadate-based heterometallic cluster known to date. The cluster is formed in organic solution and it is suggested that the bulky N-methyl-2-pyrrolidone (NMP) solvent ligands allow the isolation of this giant molecule and prevent further condensation to a solid-state metal oxide. The cluster is fully characterized using single-crystal XRD, elemental analysis, ESI mass spectrometry and other spectroscopic techniques.

  7. Three-dimensional modeling of capsule implosions in OMEGA tetrahedral hohlraums

    SciTech Connect

    Schnittman, J. D.; Craxton, R. S.

    2000-07-01

    Tetrahedral hohlraums have been proposed as a means for achieving the highly uniform implosions needed for ignition with inertial confinement fusion (ICF) [J. D. Schnittman and R. S. Craxton, Phys. Plasmas 3, 3786 (1996)]. Recent experiments on the OMEGA laser system have achieved good drive uniformity consistent with theoretical predictions [J. M. Wallace et al., Phys. Rev. Lett. 82, 3807 (1999)]. To better understand these experiments and future investigations of high-convergence ICF implosions, the three-dimensional (3-D) view-factor code BUTTERCUP has been expanded to model the time-dependent radiation transport in the hohlraum and the hydrodynamic implosion of the capsule. Additionally, a 3-D postprocessor has been written to simulate x-ray images of the imploded core. Despite BUTTERCUP's relative simplicity, its predictions for radiation drive temperatures, fusion yields, and core deformation show close agreement with experiment. (c) 2000 American Institute of Physics.

  8. Three-dimensional modeling of capsule implosions in OMEGA tetrahedral hohlraums

    NASA Astrophysics Data System (ADS)

    Schnittman, J. D.; Craxton, R. S.

    2000-07-01

    Tetrahedral hohlraums have been proposed as a means for achieving the highly uniform implosions needed for ignition with inertial confinement fusion (ICF) [J. D. Schnittman and R. S. Craxton, Phys. Plasmas 3, 3786 (1996)]. Recent experiments on the OMEGA laser system have achieved good drive uniformity consistent with theoretical predictions [J. M. Wallace et al., Phys. Rev. Lett. 82, 3807 (1999)]. To better understand these experiments and future investigations of high-convergence ICF implosions, the three-dimensional (3-D) view-factor code BUTTERCUP has been expanded to model the time-dependent radiation transport in the hohlraum and the hydrodynamic implosion of the capsule. Additionally, a 3-D postprocessor has been written to simulate x-ray images of the imploded core. Despite BUTTERCUP's relative simplicity, its predictions for radiation drive temperatures, fusion yields, and core deformation show close agreement with experiment.

  9. Structural stiffness, strength and dynamic characteristics of large tetrahedral space truss structures

    NASA Technical Reports Server (NTRS)

    Mikulas, M. M., Jr.; Bush, H. G.; Card, M. F.

    1977-01-01

    Physical characteristics of large skeletal frameworks for space applications are investigated by analyzing one concept: the tetrahedral truss, which is idealized as a sandwich plate with isotropic faces. Appropriate analytical relations are presented in terms of the truss column element properties which for calculations were taken as slender graphite/epoxy tubes. Column loads, resulting from gravity gradient control and orbital transfer, are found to be small for the class structure investigated. Fundamental frequencies of large truss structures are shown to be an order of magnitude lower than large earth based structures. Permissible loads are shown to result in small lateral deflections of the truss due to low-strain at Euler buckling of the slender graphite/epoxy truss column elements. Lateral thermal deflections are found to be a fraction of the truss depth using graphite/epoxy columns.

  10. Single walled carbon nanotube network—Tetrahedral amorphous carbon composite film

    SciTech Connect

    Iyer, Ajai Liu, Xuwen; Koskinen, Jari; Kaskela, Antti; Kauppinen, Esko I.; Johansson, Leena-Sisko

    2015-06-14

    Single walled carbon nanotube network (SWCNTN) was coated by tetrahedral amorphous carbon (ta-C) using a pulsed Filtered Cathodic Vacuum Arc system to form a SWCNTN—ta-C composite film. The effects of SWCNTN areal coverage density and ta-C coating thickness on the composite film properties were investigated. X-Ray photoelectron spectroscopy measurements prove the presence of high quality sp{sup 3} bonded ta-C coating on the SWCNTN. Raman spectroscopy suggests that the single wall carbon nanotubes (SWCNTs) forming the network survived encapsulation in the ta-C coating. Nano-mechanical testing suggests that the ta-C coated SWCNTN has superior wear performance compared to uncoated SWCNTN.

  11. Supported Tetrahedral Oxo-Sn Catalyst: Single Site, Two Modes of Catalysis

    SciTech Connect

    Beletskiy, Evgeny V.; Hou, Xianliang; Shen, Zhongliang; Gallagher, James R.; Miller, Jeffrey T.; Wu, Yuyang; Li, Tiehu; Kung, Mayfair C.; Kung, Harold H.

    2016-03-17

    Mild calcination in ozone of a (POSS)-Sn- (POSS) complex grafted on silica generated a heterogenized catalyst that mostly retained the tetrahedral coordination of its homogeneous precursor, as evidenced by spectroscopic characterizations using EXAFS, NMR, UV-vis, and DRIFT. The Sn centers are accessible and uniform and can be quantified by stoichiometric pyridine poisoning. This Sn-catalyst is active in hydride transfer reactions as a typical solid Lewis acid. However, the Sn centers can also create Brønsted acidity with alcohol by binding the alcohol strongly as alkoxide and transferring the hydroxyl H to the neighboring Sn-O-Si bond. The resulting acidic silanol is active in epoxide ring opening and acetalization reactions.

  12. Electric dipole moments in {sup 230,232}U and implications for tetrahedral shapes

    SciTech Connect

    Ntshangase, S. S.; Bark, R. A.; Datta, P.; Lawrie, E. A.; Lawrie, J. J.; Lieder, R. M.; Mullins, S. M.; Aschman, D. G.; Mohammed, H.; Stankiewicz, M. A.; Bvumbi, S.; Masiteng, P. L.; Shirinda, O.; Davidson, P. M.; Nieminen, P.; Wilson, A. N.; Dinoko, T. S.; Sharpey-Shafer, J. F.; Elbasher, M. E. A.; Juhasz, K.

    2010-10-15

    The nuclei {sup 230}U and {sup 232}U were populated in the compound nucleus reactions {sup 232}Th({alpha},6n) and {sup 232}Th({alpha},4n), respectively. Gamma rays from these nuclei were observed in coincidence with a recoil detector. A comprehensive set of in-band E2 transitions were observed in the lowest lying negative-parity band of {sup 232}U while one E2 transition was also observed for {sup 230}U. These allowed B(E1;I{sup -{yields}}I{sup +}-1)/B(E2;I{sup -{yields}}I{sup -}-2) ratios to be extracted and compared with systematics. The values are similar to those of their Th and Ra isotones. The possibility of a tetrahedral shape for the negative-parity U bands appears difficult to reconcile with the measured Q{sub 2} values for the isotone {sup 226}Ra.

  13. First-principles study of anharmonic phonon effects in tetrahedral semiconductors via an external electric field

    NASA Astrophysics Data System (ADS)

    Dabiri, Zohreh; Kazempour, Ali; Sadeghzadeh, Mohammad Ali

    2016-11-01

    The strength of phonon anharmonicity is investigated in the framework of the Density Functional Perturbation Theory via an applied constant electric field. In contrast to routine approaches, we have employed the electric field as an effective probe to quest after the quasi-harmonic and anharmonic effects. Two typical tetrahedral semiconductors (diamond and silicon) have been selected to test the efficiency of this approach. In this scheme the applied field is responsible for establishing the perturbation and also inducing the anharmonicity in systems. The induced polarization is a result of changing the electronic density while ions are located at their ground state coordinates or at a specified strain. Employing this method, physical quantities of the semiconductors are calculated in presence of the electron-phonon interaction directly and, phonon-phonon interaction, indirectly. The present approach, which is in good agreement with previous theoretical and experimental studies, can be introduced as a benchmark to simply investigate the anharmonicity and pertinent consequences in materials.

  14. Multistage structural evolution in simple monatomic supercritical fluids: superstable tetrahedral local order.

    PubMed

    Ryltsev, R E; Chtchelkatchev, N M

    2013-11-01

    The local order units of dense simple liquid are typically three-dimensional (close packed) clusters: hcp, fcc, and icosahedrons. We show that the fluid demonstrates the superstable tetrahedral local order up to temperatures several orders of magnitude higher than the melting temperature and down to critical density. While the solid-like local order (hcp, fcc) disappears in the fluid at much lower temperatures and far above critical density. We conclude that the supercritical fluid shows the temperature (density)-driven two-stage "melting" of the three-dimensional local order. We also find that the structure relaxation times in the supercritical fluid are much larger than ones estimated for weakly interactive gas even far above the melting line.

  15. Comparative morphology of configurations with reduced part count derived from the octahedral-tetrahedral truss

    NASA Technical Reports Server (NTRS)

    Lalvani, Haresh; Collins, Timothy J.

    1991-01-01

    Morphology (the study of structure and form) of the octahedral-tetrahedral (octet) truss is described. Both the geometry and symmetry of the octet truss are considered. Morphological techniques based on symmetry operations are presented which enable the derivation of reduced-part-count truss configurations from the octet truss by removing struts and nodes. These techniques are unique because their Morphological origination and they allow for the systematic generation and analysis of a large variety of structures. Methods for easily determining the part count and redundancy of infinite truss configurations are presented. Nine examples of truss configurations obtained by applying the derivation techniques are considered. These configurations are structurally stable while at the same time exhibiting significant reductions in part count. Some practical and analytical considerations, such as structural performance, regarding the example reduced-part-count truss geometries are briefly discussed.

  16. Electrochemical switching with 3D DNA tetrahedral nanostructures self-assembled at gold electrodes.

    PubMed

    Abi, Alireza; Lin, Meihua; Pei, Hao; Fan, Chunhai; Ferapontova, Elena E; Zuo, Xiaolei

    2014-06-11

    Nanomechanical switching of functional three-dimensional (3D) DNA nanostructures is crucial for nanobiotechnological applications such as nanorobotics or self-regulating sensor and actuator devices. Here, DNA tetrahedral nanostructures self-assembled onto gold electrodes were shown to undergo the electronically addressable nanoswitching due to their mechanical reconfiguration upon external chemical stimuli. That enables construction of robust surface-tethered electronic nanodevices based on 3D DNA tetrahedra. One edge of the tetrahedron contained a partially self-complementary region with a stem-loop hairpin structure, reconfigurable upon hybridization to a complementary DNA (stimulus DNA) sequence. A non-intercalative ferrocene (Fc) redox label was attached to the reconfigurable tetrahedron edge in such a way that reconfiguration of this edge changed the distance between the electrode and Fc.

  17. Evaluation of a 3D point cloud tetrahedral tomographic reconstruction method

    PubMed Central

    Pereira, N F; Sitek, A

    2011-01-01

    Tomographic reconstruction on an irregular grid may be superior to reconstruction on a regular grid. This is achieved through an appropriate choice of the image space model, the selection of an optimal set of points and the use of any available prior information during the reconstruction process. Accordingly, a number of reconstruction-related parameters must be optimized for best performance. In this work, a 3D point cloud tetrahedral mesh reconstruction method is evaluated for quantitative tasks. A linear image model is employed to obtain the reconstruction system matrix and five point generation strategies are studied. The evaluation is performed using the recovery coefficient, as well as voxel- and template-based estimates of bias and variance measures, computed over specific regions in the reconstructed image. A similar analysis is performed for regular grid reconstructions that use voxel basis functions. The maximum likelihood expectation maximization reconstruction algorithm is used. For the tetrahedral reconstructions, of the five point generation methods that are evaluated, three use image priors. For evaluation purposes, an object consisting of overlapping spheres with varying activity is simulated. The exact parallel projection data of this object are obtained analytically using a parallel projector, and multiple Poisson noise realizations of these exact data are generated and reconstructed using the different point generation strategies. The unconstrained nature of point placement in some of the irregular mesh-based reconstruction strategies has superior activity recovery for small, low-contrast image regions. The results show that, with an appropriately generated set of mesh points, the irregular grid reconstruction methods can out-perform reconstructions on a regular grid for mathematical phantoms, in terms of the performance measures evaluated. PMID:20736496

  18. Quantifying tetrahedral adduct formation and stabilization in the cysteine and the serine proteases.

    PubMed

    Cleary, Jennifer A; Doherty, William; Evans, Paul; Malthouse, J Paul G

    2015-10-01

    Two new papain inhibitors have been synthesized where the terminal α-carboxyl groups of Z-Phe-Ala-COOH and Ac-Phe-Gly-COOH have been replaced by a proton to give Z-Phe-Ala-H and Ac-Phe-Gly-H. We show that for papain, replacing the terminal carboxylate group of a peptide inhibitor with a hydrogen atom decreases binding 3-4 fold while replacing an aldehyde or glyoxal group with a hydrogen atom decreases binding by 300,000-1,000,000 fold. Thiohemiacetal formation by papain with aldehyde or glyoxal inhibitors is shown to be ~10,000 times more effective than hemiacetal or hemiketal formation with chymotrypsin. It is shown using effective molarities, that for papain, thiohemiacetal stabilization is more effective with aldehyde inhibitors than with glyoxal inhibitors. The effective molarity obtained when papain is inhibited by an aldehyde inhibitor is similar to the effective molarity obtained when chymotrypsin is inhibited by glyoxal inhibitors showing that both enzymes can stabilize tetrahedral adducts by similar amounts. Therefore the greater potency of aldehyde and glyoxal inhibitors with papain is not due to greater thiohemiacetal stabilization by papain compared to the hemiketal and hemiacetal stabilization by chymotrypsin, instead it reflects the greater intrinsic reactivity of the catalytic thiol group of papain compared to the catalytic hydroxyl group of chymotrypsin. It is argued that while the hemiacetals and thiohemiacetals formed with the serine and cysteine proteases respectively can mimic the catalytic tetrahedral intermediate they are also analogues of the productive and non-productive acyl intermediates that can be formed with the cysteine and serine proteases.

  19. Organometallic Polymeric Conductors

    NASA Technical Reports Server (NTRS)

    1997-01-01

    For aerospace applications, the use of polymers can result in tremendous weight savings over metals. Suitable polymeric materials for some applications like EMI shielding, spacecraft grounding, and charge dissipation must combine high electrical conductivity with long-term environmental stability, good processability, and good mechanical properties. Recently, other investigators have reported hybrid films made from an electrically conductive polymer combined with insulating polymers. In all of these instances, the films were prepared by infiltrating an insulating polymer with a precursor for a conductive polymer (either polypyrrole or polythiophene), and oxidatively polymerizing the precursor in situ. The resulting composite films have good electrical conductivity, while overcoming the brittleness inherent in most conductive polymers. The highest conductivities reported (approximately 4/Scm) were achieved with polythiophene in a polystyrene host polymer. The best films using a polyamide as base polymer were four orders of magnitude less conductive than the polystyrene films. The authors suggested that this was because polyimides were unable to swell sufficiently for infiltration of monomer as in the polystyrene. It was not clear, however, if the different conductivities obtained were merely the result of differing oxidation conditions. Oxidation time, temperature and oxidant concentration varied widely among the studies.

  20. Gratings in polymeric waveguides

    NASA Astrophysics Data System (ADS)

    Mishakov, G.; Sokolov, V.; Kocabas, A.; Aydinli, A.

    2007-04-01

    Laser-induced formation of polymer Bragg grating filters for Dense Wavelength Division Multiplexing (DWDM) applications is discussed. Acrylate monomers halogenated with both fluorine and chlorine, which possess absorption losses less than 0.25 dB/cm and wide choice of refractive indices (from 1.3 to 1.5) in the 1.5 μm telecom wavelength region were used. The monomers are highly intermixable thus permitting to adjust the refractive index of the composition within +/-0.0001. Moreover they are photocurable under UV exposure and exhibit high contrast in polymerization. These properties make halogenated acrylates very promising for fabricating polymeric waveguides and photonic circuits. Single-mode polymer waveguides were fabricated on silicon wafers using resistless contact lithography. Submicron index gratings have been written in polymer waveguides using holographic exposure with He-Cd laser beam (325 nm) through a phase mask. Both uniform and apodized gratings have been fabricated. The gratings are stable and are not erased by uniform UV exposure. The waveguide gratings possess narrowband reflection spectra in the 1.5 μm wavelength region of 0.4 nm width, nearly rectangular shape of the stopband and reflectivity R > 99%. The fabricated Bragg grating filters can be used for multiplexing/demultiplexing optical signals in high-speed DWDM optical fiber networks.

  1. Reactions of the tetrahedral clusters [MCo(3)(CO)(12)](-) (M = Ru, Fe) with functional mono- and diynes.

    PubMed

    Choualeb, Aldjia; Braunstein, Pierre; Rosé, Jacky; Welter, Richard

    2004-01-12

    The tetrahedral cluster [RuCo(3)(CO)(12)](-) reacts with various alkynes, including the new PhCtbd1;CC(O)NHCH(2)Ctbd1;CH (L(1)()), to afford the butterfly clusters [RuCo(3)(CO)(10)(micro(4)-eta(2)-RC(2)R')](-) (1, R = R' = C(O)OMe; 2, R = H, R' = Ph; 3, R = H, R' = MeC=CH(2); 4, R = H, R' = CH(2)OCH(2)Ctbd1;CH; 5, R = H, R' = CH(2)NHC(O)Ctbd1;CPh), in which the ruthenium atom occupies a hinge position and the alkyne is coordinated in a micro(4)-eta(2) fashion. Reaction of the anions 1-3 with [Cu(NCMe)(4)]BF(4) led to selective loss of the 12e fragment Co(CO)(-) to form [RuCo(2)(CO)(9)(micro(3)-eta(2)-RC(2)R')] (6, R = R' = C(O)OMe; 7, R = H, R' = Ph; 8, R = H, R' = MeC=CH(2)). To prepare functionalized RuCo(3) or FeCo(3) clusters that could be subsequently condensed with a silica matrix via the sol-gel method, we reacted [MCo(3)(CO)(12)](-) (M = Ru, Fe) with the alkyne PhCtbd1;CC(O)NH(CH(2))(3)Si(OMe)(3)(L(2)()) and obtained the butterfly clusters [MCo(3)(CO)(10)(micro(4)-eta(2)-PhC(2)C(O)NH(CH(2))(3)Si(OMe)(3))](-) 9 and 10, respectively. Air-stable [RuCo(3)(CO)(10)(micro(4)-eta(2)-Me(3)SiC(2)Ctbd1;CSiMe(3))](-) (11) was obtained from 1,4-bis(trimethylsilyl)butadiyne and reacted with [Cu(NCMe)(4)]BF(4) to give [RuCo(2)(CO)(9)(micro(3)-eta(2)-HC(2)Ctbd1;CSiMe(3))] (12), owing to partial ligand proto-desilylation, and not the expected [RuCo(2)(CO)(9)(micro(3)-eta(2)-Me(3)SiC(2)Ctbd1;CSiMe(3))]. Reaction of 11 with [NO]BF(4) afforded, in addition to 12, [RuCo(3)(CO)(9)(NO)(micro(4)-eta(2)-Me(3)SiC(2)Ctbd1;CSiMe(3))] (13) owing to selective CO substitution on a wing-tip cobalt atom with NO. The thermal reaction of 11 with [AuCl(PPh(3))] led to replacement of a CO on Ru by the PPh(3) originating from [AuCl(PPh(3))] and afforded [RuCo(3)(CO)(9)(PPh(3))(micro(4)-eta(2)-Me(3)SiC(2)Ctbd1;CSiMe(3))](-) (14), also obtained directly by reaction of 11 with one equivalent of PPh(3). Proto-desilylation of 11 using TBAF/THF-H(2)O afforded [RuCo(3)(CO)(10)(micro(4)-eta(2)-Me(3)Si

  2. Non-Isocyanate Polyurethane Soft Nanoparticles Obtained by Surfactant-Assisted Interfacial Polymerization.

    PubMed

    Bossion, Amaury; Jones, Gavin O; Taton, Daniel; Mecerreyes, David; Hedrick, James L; Ong, Zhan Yuin; Yang, Yi Yan; Sardon, Haritz

    2017-02-28

    Polyurethanes (PUs) are considered ideal candidates for drug delivery applications due to their easy synthesis, excellent mechanical properties, and biodegradability. Unfortunately, methods for preparing well-defined PU nanoparticles required miniemulsion polymerization techniques with a nontrivial control of the polymerization conditions due to the inherent incompatibility of isocyanate-containing monomers and water. In this work, we report the preparation of soft PU nanoparticles in a one-pot process using interfacial polymerization that employs a non-isocyanate polymerization route that minimizes side reactions with water. Activated pentafluorophenyl dicarbonates were polymerized with diamines and/or triamines by interfacial polymerization in the presence of an anionic emulsifier, which afforded non-isocyanate polyurethane (NIPU) nanoparticles with sizes in the range of 200-300 nm. Notably, 5 wt % of emulsifier was required in combination with a trifunctional amine to achieve stable PU dispersions and avoid particle aggregation. The versatility of this polymerization process allows for incorporation of functional groups into the PU nanoparticles, such as carboxylic acids, which can encapsulate the chemotherapeutic doxorubicin through ionic interactions. Altogether, this waterborne synthetic method for functionalized NIPU soft nanoparticles holds great promise for the preparation of drug delivery nanocarriers.

  3. Photoinitiated polymerization of methyl methacrylate using Q-sized ZnO colloids

    SciTech Connect

    Hoffman, A.J.; Yee, H.; Mills, G.; Hoffmann, M.R.

    1992-06-25

    Q-sized ZnO particles are determined to be efficient photoinitiators of methyl methacrylate polymerization. The effects of semiconductor particle size, solvent, initiator concentration, monomer concentration, and light intensity on reaction rates are examined. The reaction path is initiated anionically, followed by free-radical propogation steps. Polymerization increases with increased photoinitiator and monomer concentration and particle size; it also has a dependence upon the square root of the light intensity. Illumination-induced holes are scavenged by the solvent. 29 refs., 8 figs., 2 tabs.

  4. Electronic Transitions as a Probe of Tetrahedral versus Octahedral Coordination in Nickel(II) Complexes: An Undergraduate Inorganic Chemistry Experiment.

    ERIC Educational Resources Information Center

    Filgueiras, Carlos A. L.; Carazza, Fernando

    1980-01-01

    Discusses procedures, theoretical considerations, and results of an experiment involving the preparation of a tetrahedral nickel(II) complex and its transformation into an octahedral species. Suggests that fundamental aspects of coordination chemistry can be demonstrated by simple experiments performed in introductory level courses. (Author/JN)

  5. The role of fcc tetrahedral subunits in the phase behavior of medium sized Lennard-Jones clusters.

    PubMed

    Saika-Voivod, Ivan; Poon, Louis; Bowles, Richard K

    2010-08-21

    The free energy of a 600-atom Lennard-Jones cluster is calculated as a function of surface and bulk crystallinity in order to study the structural transformations that occur in the core of medium sized clusters. Within the order parameter range studied, we find the existence of two free energy minima at temperatures near freezing. One minimum, at low values of both bulk and surface order, belongs to the liquid phase. The second minimum exhibits a highly ordered core with a disordered surface and is related to structures containing a single fcc-tetrahedral subunit, with an edge length of seven atoms (l=7), located in the particle core. At lower temperatures, a third minimum appears at intermediate values of the bulk order parameter which is shown to be related to the formation of multiple l=6 tetrahedra in the core of the cluster. We also use molecular dynamics simulations to follow a series of nucleation events and find that the clusters freeze to structures containing l=5, 6, 7, and 8 sized tetrahedra as well as those containing no tetrahedral units. The structural correlations between bulk and surface order with the size of the tetrahedral units in the cluster core are examined. Finally, the relationships between the formation of fcc tetrahedral subunits in the core, the phase behavior of medium sized clusters and the nucleation of noncrystalline global structures such as icosahedra and decahedra are discussed.

  6. Electronic Transitions as a Probe of Tetrahedral versus Octahedral Coordination in Nickel(II) Complexes: An Undergraduate Inorganic Chemistry Experiment.

    ERIC Educational Resources Information Center

    Filgueiras, Carlos A. L.; Carazza, Fernando

    1980-01-01

    Discusses procedures, theoretical considerations, and results of an experiment involving the preparation of a tetrahedral nickel(II) complex and its transformation into an octahedral species. Suggests that fundamental aspects of coordination chemistry can be demonstrated by simple experiments performed in introductory level courses. (Author/JN)

  7. Perpendicularly Aligned, Anion Conducting Nanochannels in Block Copolymer Electrolyte Films

    SciTech Connect

    Arges, Christopher G.; Kambe, Yu; Suh, Hyo Seon; Ocola, Leonidas E.; Nealey, Paul F.

    2016-03-08

    Connecting structure and morphology to bulk transport properties, such as ionic conductivity, in nanostructured polymer electrolyte materials is a difficult proposition because of the challenge to precisely and accurately control order and the orientation of the ionic domains in such polymeric films. In this work, poly(styrene-block-2-vinylpyridine) (PSbP2VP) block copolymers were assembled perpendicularly to a substrate surface over large areas through chemical surface modification at the substrate and utilizing a versatile solvent vapor annealing (SVA) technique. After block copolymer assembly, a novel chemical vapor infiltration reaction (CVIR) technique selectively converted the 2-vinylpyridine block to 2-vinyl n-methylpyridinium (NMP+ X-) groups, which are anion charge carriers. The prepared block copolymer electrolytes maintained their orientation and ordered nanostructure upon the selective introduction of ion moieties into the P2VP block and post ion-exchange to other counterion forms (X- = chloride, hydroxide, etc.). The prepared block copolymer electrolyte films demonstrated high chloride ion conductivities, 45 mS cm(-1) at 20 degrees C in deionized water, the highest chloride ion conductivity for anion conducting polymer electrolyte films. Additionally, straight-line lamellae of block copolymer electrolytes were realized using chemoepitaxy and density multiplication. The devised scheme allowed for precise and accurate control of orientation of ionic domains in nanostructured polymer electrolyte films and enables a platform for future studies that examines the relationship between polymer electrolyte structure and ion transport.

  8. Coating of plasma polymerized film

    NASA Technical Reports Server (NTRS)

    Morita, S.; Ishibashi, S.

    1980-01-01

    Plasma polymerized thin film coating and the use of other coatings is suggested for passivation film, thin film used for conducting light, and solid body lubrication film of dielectrics of ultra insulators for electrical conduction, electron accessories, etc. The special features of flow discharge development and the polymerized film growth mechanism are discussed.

  9. Amplification of actin polymerization forces

    PubMed Central

    Dmitrieff, Serge; Nédélec, François

    2016-01-01

    The actin cytoskeleton drives many essential processes in vivo, using molecular motors and actin assembly as force generators. We discuss here the propagation of forces caused by actin polymerization, highlighting simple configurations where the force developed by the network can exceed the sum of the polymerization forces from all filaments. PMID:27002174

  10. Amplification of actin polymerization forces.

    PubMed

    Dmitrieff, Serge; Nédélec, François

    2016-03-28

    The actin cytoskeleton drives many essential processes in vivo, using molecular motors and actin assembly as force generators. We discuss here the propagation of forces caused by actin polymerization, highlighting simple configurations where the force developed by the network can exceed the sum of the polymerization forces from all filaments.

  11. Platelet interaction with polymerizing fibrin.

    PubMed

    Niewiarowski, S; Regoeczi, E; Stewart, G J; Senyl, A F; Mustard, J F

    1972-03-01

    Interaction of washed pig, rabbit, or human platelets with fibrinogen was studied during its transition to fibrin using photometric, isotopic, and electron microscopic techniques. Untreated fibrinogen and fully polymerized fibrin had no detectable effect on platelets. Fibrinogen, incubated with low concentrations of reptilase or thrombin, formed intermediate products which readily became associated with platelets and caused their aggregation. Neutralization of the thrombin did not prevent this interaction. In the absence of fibrinogen, reptilase did not affect platelets. The interaction of polymerizing fibrin with platelets was accompanied by small losses of platelet constituents (serotonin, adenine nucleotides, platelet factor 4, and lactic dehydrogenase). This loss did not appear to be the result of the platelet release reaction. Inhibitors of the release reaction or of adenosine diphosphate (ADP)-induced aggregation did not prevent the interaction of platelets with polymerizing fibrin. Apyrase or prostaglandin E(1) (PGE(1)) reduced the extent of platelet aggregation by polymerizing fibrin, but the amount of protein associated with platelets was slightly increased. The interaction of polymerizing fibrin with platelets was completely inhibited by ethylenediaminetetraacetate (EDTA) or ethylene glycol bis (beta-aminoethyl ether) N, N,N',N'-tetraacetic acid (EGTA).Fibers formed in solutions of polymerizing fibrin were larger in the presence than in the absence of washed platelets, suggesting that platelets affect fibrin polymerization. The adherence of platelets to polymerizing fibrin may be responsible for the establishment of links between platelets and fibrin in hemostatic plugs and thrombi.

  12. Vibrational Autodetachment in Nitroalkane Anions

    NASA Astrophysics Data System (ADS)

    Adams, Christopher L.; Weber, J. Mathias

    2010-06-01

    Nitroalkanes have electron affinities ge 1370 cm-1, well below the excitation energies for CH stretching modes, with the excess charge localized on the nitro group. Upon absorption of an IR photon in a CH stretching vibrational mode, the absorbed energy is redistributed in the molecule. If enough energy is transferred to the NO2 stretching/wagging modes, the excess electron residing on the nitro group is emitted. Vibrational autodetachment (VAD) spectra encode information regarding intramolecular vibrational relaxation (IVR) processes leading up to electron emission. We present VAD photoelectron spectroscopy of polyatomic molecular anions and discuss how a VAD photoelectron spectrum can be modeled.

  13. Synthesis and structure of Li 4Sr 3Ge 2N 6: a new quaternary nitride containing Ge 2N 610- anions

    NASA Astrophysics Data System (ADS)

    Park, Dong Gon; Gál, Zoltán A.; DiSalvo, Francis J.

    2003-04-01

    A new Li-containing quaternary nitride, Li 4Sr 3Ge 2N 6, was obtained as single crystals from constituent elements in molten Na. It crystallizes in space group C2/ m (No. 12) with a=6.1398(7) Å, b=10.021(1) Å, c=6.3130(7) Å, β=91.279(2)°, and Z=2. It contains the first example of isolated nitridogermanate anions of Ge 2N 610-, which is also the first example of edge-sharing tetrahedral [GeN 4].

  14. Pyrazole complexes as anion receptors.

    PubMed

    Nieto, Sonia; Pérez, Julio; Riera, Lucía; Riera, Víctor; Miguel, Daniel

    2006-03-01

    The behavior of the receptors [Re(CO)3(Hdmpz)3]BAr'4 (Hdmpz = 3,5-dimethylpyrazole) (1) and [Re(CO)3(HtBupz)3]BAr'4 (HtBupz = 3(5)-tert-butylpyrazole) (2; Ar' = 3,5-bis(trifluoromethyl)phenyl) toward the anions fluoride, chloride, bromide, iodide, hydrogensulfate, dihydrogenphosphate, nitrate, and perrhenate was studied in CD3CN solution. In most cases, the receptors were stable. Anion exchange was fast, and binding constants were calculated from the NMR titration profiles. The structure of the adduct [Re(CO)3(HtBupz)3] x NO3 (3) was determined by X-ray diffraction. Two pyrazole moieties are hydrogen-bonded to one nitrate oxygen atom, and the third pyrazole moiety is hydrogen-bonded to an oxygen atom of an adjacent nitrate, leading to infinite chains. The structure of the adduct [Re(CO)3(Hdmpz)3]BAr'4acetone (4), also determined by X-ray diffraction, showed a similar interaction of two pyrazole N-H groups with the acetone oxygen atom. F- and H2PO4(-) deprotonate the receptors, and HSO4(-) decomposed 1. The structure of one of the decomposition products (5), determined by X-ray diffraction, is consistent with pyrazole protonation and substitution by sulfate.

  15. Tunable electronic interactions between anions and perylenediimide.

    PubMed

    Goodson, Flynt S; Panda, Dillip K; Ray, Shuvasree; Mitra, Atanu; Guha, Samit; Saha, Sourav

    2013-08-07

    Over the past decade anion-π interaction has emerged as a new paradigm of supramolecular chemistry of anions. Taking advantage of the electronic nature of anion-π interaction, we have expanded its boundaries to charge-transfer (CT) and formal electron transfer (ET) events by adjusting the electron-donating and accepting abilities of anions and π-acids, respectively. To establish that ET, CT, and anion-π interactions could take place between different anions and π-acids as long as their electronic and structural properties are conducive, herein, we introduce 3,4,9,10-perylenediimide (PDI-1) that selectively undergoes thermal ET from strong Lewis basic hydroxide and fluoride anions, but remains electronically and optically silent to poor Lewis basic anions, as ET and CT events are turned OFF. These interactions have been fully characterized by UV/Vis, NMR, and EPR spectroscopies. These results demonstrate the generality of anion-induced ET events in aprotic solvents and further refute a notion that strong Lewis basic hydroxide and fluoride ions can only trigger nucleophilic attack to form covalent bonds instead of acting as sacrificial electron donors to π-acids under appropriate conditions.

  16. A new copper borophosphate with novel polymeric chains and its structural correlation with raw materials in molten hydrated flux synthesis

    SciTech Connect

    Duan, Ruijing; Liu, Wei Cao, Lixin; Su, Ge; Xu, Hongmei; Zhao, Chenggong

    2014-02-15

    A novel copper borophosphate, Cu{sub 3}[B{sub 2}P{sub 3}O{sub 12}(OH){sub 3}] has been prepared by the molten hydrated flux method. Its crystal structure was determined by the single-crystal X-ray diffraction (monoclinic, Cc, a=6.1895 Å, b=13.6209 Å, c=11.9373 Å, β=97.62°, V=997.5 Å{sup 3}, Z=4). The three-dimensional framework of the titled compound, is composed by two kinds of polymeric chains and isolated PO{sub 4} tetrahedral. One novel 4-membered tetrahedral rings has been observed in borophosphates. Magnetic measurements indicate that the title compound exits antiferromagnetic interactions. Due to the special reaction medium created by the molten hydrated flux method, a possible structural correlation between the final solids and the raw materials has been noted. - Graphical abstract: The 3D structure consists of a framework composed of CuO{sub x} polyhedra, BO{sub 4} and PO{sub 4} tetrahedra. A intersection angle between the metal chains and borophosphate chains can be noted. Display Omitted - Highlights: • A novel copper borophosphate has been prepared by the molten hydrated flux method. • One novel 4-membered tetrahedral ring has been observed firstly in borophosphates. • A possible structural correlation between the final solids and the raw materials has been noted.

  17. Interpenetrating metal-organic frameworks formed by self-assembly of tetrahedral and octahedral building blocks

    SciTech Connect

    Lu Yongming; Lan Yaqian; Xu Yanhong; Su Zhongmin; Li Shunli; Zang Hongying; Xu Guangjuan

    2009-11-15

    To investigate the relationship between topological types and molecular building blocks (MBBs), we have designed and synthesized a series of three-dimensional (3D) interpenetrating metal-organic frameworks based on different polygons or polyhedra under hydrothermal conditions, namely [Cd(bpib){sub 0.5}(L{sup 1})] (1), [Cd(bpib){sub 0.5}(L{sup 2})].H{sub 2}O (2), [Cd(bpib){sub 0.5}(L{sup 3})] (3) and [Cd(bib){sub 0.5}(L{sup 1})] (4), where bpib=1,4-bis(2-(pyridin-2-yl)-1H-imidazol-1-yl)butane, bib=1,4-bis(1H-imidazol-1-yl)butane, H{sub 2}L{sup 1}=4-(4-carboxybenzyloxy)benzoic acid, H{sub 2}L{sup 2}=4,4'-(ethane-1,2-diylbis(oxy))dibenzoic acid and H{sub 2}L{sup 3}=4,4'-(1,4-phenylenebis(methylene))bis(oxy)dibenzoic acid, respectively. Their structures have been determined by single crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra, and thermogravimetric (TG) analyses. Compounds 1-3 display alpha-Po topological nets with different degrees of interpenetration based on the similar octahedral [Cd{sub 2}(-COO){sub 4}] building blocks. Compound 4 is a six-fold interpenetrating diamondoid net based on tetrahedral MBBs. By careful inspection of these structures, we find that various carboxylic ligands and N-donor ligands with different coordination modes and conformations, and metal centers with different geometries are important for the formation of the different MBBs. It is believed that different topological types lie on different MBBs with various polygons or polyhedra. Such as four- and six-connected topologies are formed by tetrahedral and octahedral building blocks. In addition, with the increase of carboxylic ligands' length, the degrees of interpenetration have been changed in the alpha-Po topological nets. And the luminescent properties of these compounds have been investigated in detail. - Graphical abstract: A series of three-dimensional interpenetrating metal-organic frameworks based on different polygons or polyhedra

  18. The synthesis and complex anion-vacancy ordered structure of La{sub 0.33}Sr{sub 0.67}MnO{sub 2.42}

    SciTech Connect

    Dixon, Edward; Hadermann, Joke; Hayward, Michael A.

    2011-07-15

    The low-temperature topotactic reduction of La{sub 0.33}Sr{sub 0.67}MnO{sub 3} with NaH results in the formation of La{sub 0.33}Sr{sub 0.67}MnO{sub 2.42}. A combination of neutron powder and electron diffraction data show that La{sub 0.33}Sr{sub 0.67}MnO{sub 2.42} adopts a novel anion-vacancy ordered structure with a 6-layer OOTOOT' stacking sequence of the 'octahedral' and tetrahedral layers (Pcmb, a=5.5804(1) A, b=23.4104(7) A, c=11.2441(3) A). A significant concentration of anion vacancies at the anion site, which links neighbouring 'octahedral' layers means that only 25% of the 'octahedral' manganese coordination sites actually have 6-fold MnO{sub 6} coordination, the remainder being MnO{sub 5} square-based pyramidal sites. The chains of cooperatively twisted apex-linked MnO{sub 4} tetrahedra adopt an ordered -L-R-L-R- arrangement within each tetrahedral layer. This is the first published example of a fully refined structure of this type which exhibits such intralayer ordering of the twisted tetrahedral chains. The rationale behind the contrasting structures of La{sub 0.33}Sr{sub 0.67}MnO{sub 2.42} and other previously reported reduced La{sub 1-x}Sr{sub x}MnO{sub 3-y} phases is discussed. - Graphical Abstract: The topotactic reduction of the perovskite phase La{sub 0.33}Sr{sub 0.67}MnO{sub 3} with NaH yields La{sub 0.33}Sr{sub 0.67}MnO{sub 2.42(3)}, which adopts a novel anion vacancy ordered structure with a 6-layer OOTOOT' stacking sequence of the 'octahedral' and tetrahedral layers. The anion site that links the neighbouring octahedral layers is partially occupied so only 25% of the 'octahedral' manganese sites actually have 6-fold MnO{sub 6} coordination. Highlights: > Topotactic reduction with NaH to form a mixed valent Mn{sup 2+}/Mn{sup 3+} phase. > Novel layered anion-vacancy ordered structure. > Comparison to related brownmillerite structure types.

  19. Anion adsorption induced surface reconstructions

    NASA Astrophysics Data System (ADS)

    Tang, Lei

    2005-11-01

    Surface stress plays an important role in the behavior of solid surfaces. Potential-controlled anion adsorption in electrolytes alters the surface stress of the electrode and results in morphology changes to the surfaces. With a combination of potential-induced surface stress measurement and in situ electrochemical scanning tunneling microscopy (STM), it is demonstrated that anion adsorption induces changes in structure of thin films and modifies the growth morphology and stress evolution in epitaxially grown films. Surface structural transitions in the heteroepitaxial system consisting of one to two gold monolayers on platinum substrates were observed. By increasing the potential, structural transitions, from (1 x 1), to a striped phase, to a hexagonal structure, occurred in the gold bilayer. This hexagonal structure was related to the formation of an ordered sulfate adlayer with a ( 3x7 ) structure. Such transitions were repeatable by cycling the potential. Furthermore, the transitions between various dislocation structures were affected by anion adsorption. The surface composition of the gold bilayer on Pt was measured by underpotential deposition of copper. By subtracting the contribution of a pure Pt surface from the gold bi-layer on Pt, a stress change of -2.4 N/m was observed, which agrees with the stress change of -2.46 N/m predicted to accompany formation of 1.5 MLs of coherent Au on Pt(111) from epitaxy theory. The Cu monolayer deposited on Au(111) from an acid sulfate electrolyte was found to be pseudomorphic while the Cu monolayer formed on Au(111) in vacuum was incoherent. The stress-thickness change associated with the coherent monolayer of copper on Au(111) in electrolyte was -0.6 N/m, while conventional epitaxy theories predict a value of +7.76 N/m. STM results elucidated the sulfate adsorption on the copper monolayer caused an expansion of the layer as evidenced by a Moire Structure. For the Cu monolayer on Au(111), the sulfate-induced expansion

  20. Polymeric potassium triformatocobalt(II)

    PubMed Central

    Wöhlert, Susanne; Wriedt, Mario; Jess, Inke; Näther, Christian

    2011-01-01

    In the crystal structure of the title compound, poly[tri-μ-formato-cobalt(II)potassium], [CoK(CHO2)3]n the Co2+ cations are coordinated by six O-bonded formate anions in an octa­hedral coordination mode and the K+ cations are eightfold coordinated by seven O-bonded formate anions within irregular polyhedra. The Co2+ cations are connected by bridging formate anions into a three-dimensional coordination network in which the K+ cations are embedded. The asymmetric unit consits of one Co2+ cation located on a center of inversion, one K+ cation located on a twofold axis and two crystallographically independent formato anions, of which one is located on a twofold axis and the other occupies a general position. PMID:21753951

  1. Production of monodisperse, polymeric microspheres

    NASA Technical Reports Server (NTRS)

    Rembaum, Alan (Inventor); Rhim, Won-Kyu (Inventor); Hyson, Michael T. (Inventor); Chang, Manchium (Inventor)

    1990-01-01

    Very small, individual polymeric microspheres with very precise size and a wide variation in monomer type and properties are produced by deploying a precisely formed liquid monomer droplet, suitably an acrylic compound such as hydroxyethyl methacrylate into a containerless environment. The droplet which assumes a spheroid shape is subjected to polymerizing radiation such as ultraviolet or gamma radiation as it travels through the environment. Polymeric microspheres having precise diameters varying no more than plus or minus 5 percent from an average size are recovered. Many types of fillers including magnetic fillers may be dispersed in the liquid droplet.

  2. Melting line of polymeric nitrogen

    NASA Astrophysics Data System (ADS)

    Yakub, L. N.

    2013-05-01

    We made an attempt to predict location of the melting line of polymeric nitrogen using two equations for Helmholtz free energy: proposed earlier for cubic gauche-structure and developed recently for liquid polymerized nitrogen. The P-T relation, orthobaric densities and latent heat of melting were determined using a standard double tangent construction. The estimated melting temperature decreases with increasing pressure, alike the temperature of molecular-nonmolecular transition in solid. We discuss the possibility of a triple point (solid-molecular fluid-polymeric fluid) at ˜80 GPa and observed maximum of melting temperature of nitrogen.

  3. Organometallic Polymeric Conductors

    NASA Technical Reports Server (NTRS)

    Youngs, Wiley J.

    1997-01-01

    For aerospace applications, the use of polymers can result in tremendous weight savings over metals. Suitable polymeric materials for some applications like EMI shielding, spacecraft grounding, and charge dissipation must combine high electrical conductivity with long-term environmental stability, good processability, and good mechanical properties. Recently, other investigators have reported hybrid films made from an electrically conductive polymer combined with insulating polymers. In all of these instances, the films were prepared by infiltrating an insulating polymer with a precursor for a conductive polymer (either polypyrrole or polythiophene), and oxidatively polymerizing the precursor in situ. The resulting composite films have good electrical conductivity, while overcoming the brittleness inherent in most conductive polymers. Many aerospace applications require a combination of properties. Thus, hybrid films made from polyimides or other engineering resins are of primary interest, but only if conductivities on the same order as those obtained with a polystyrene base could be obtained. Hence, a series of experiments was performed to optimize the conductivity of polyimide-based composite films. The polyimide base chosen for this study was Kapton. 3-MethylThiophene (3MT) was used for the conductive phase. Three processing variables were identified for producing these composite films, namely time, temperature, and oxidant concentration for the in situ oxidation. Statistically designed experiments were used to examine the effects of these variables and synergistic/interactive effects among variables on the electrical conductivity and mechanical strength of the films. Multiple linear regression analysis of the tensile data revealed that temperature and time have the greatest effect on maximum stress. The response surface of maximum stress vs. temperature and time (for oxidant concentration at 1.2 M) is shown. Conductivity of the composite films was measured for

  4. High temperature structural, polymeric foams from high internal emulsion polymerization

    SciTech Connect

    Hoisington, M.A.; Duke, J.R.; Apen, P.G.

    1996-02-01

    In 1982, a high internal phase emulsion (HIPE) polymerization process to manufacture microcellular, polymeric foam systems was patented by Unilever. This patent discloses a polymerization process that occurs in a water-in-oil emulsion in which the water represents at least 76% of the emulsion by volume. The oil phase consists of vinyl monomers such as styrene and acrylates that are crosslinked by divinyl monomers during polymerization. After polymerization and drying to remove the water phase, the result is a crosslinked polymer foam with an open cell microstructure that is homogeneous throughout in terms of morphology, density, and mechanical properties. Since 1982, numerous patents have examined various HIPE polymerized foam processing techniques and applications that include absorbents for body fluids, cleaning materials, and ion exchange systems. All the published HIPE polymerized foams have concentrated on materials for low temperature applications. Copolymerization of styrene with maleic anhydride and N-substituted maleimides to produce heat resistant thermoplastics has been studied extensively. These investigations have shown that styrene will free radically copolymerize with N-substituted maleimides to create an alternating thermoplastic copolymer with a Tg of approximately 200{degrees}C. However, there are many difficulties in attempting the maleimide styrene copolymerization in a HIPE such as lower polymerization temperatures, maleimide solubility difficulties in both styrene and water, and difficulty obtaining a stable HIPE with a styrene/maleimide oil phase. This work describes the preparation of copolymer foams from N-ethylmaleimide and Bis(3-ethyl-5-methyl-4-maleimide-phenyl)methane with styrene based monomers and crosslinking agents.

  5. Cause and Cure - Deterioration in Accuracy of CFD Simulations With Use of High-Aspect-Ratio Triangular Tetrahedral Grids

    NASA Technical Reports Server (NTRS)

    Chang, Sin-Chung; Chang, Chau-Lyan; Venkatachari, Balaji Shankar

    2017-01-01

    Traditionally high-aspect ratio triangular/tetrahedral meshes are avoided by CFD re-searchers in the vicinity of a solid wall, as it is known to reduce the accuracy of gradient computations in those regions and also cause numerical instability. Although for certain complex geometries, the use of high-aspect ratio triangular/tetrahedral elements in the vicinity of a solid wall can be replaced by quadrilateral/prismatic elements, ability to use triangular/tetrahedral elements in such regions without any degradation in accuracy can be beneficial from a mesh generation point of view. The benefits also carry over to numerical frameworks such as the space-time conservation element and solution element (CESE), where triangular/tetrahedral elements are the mandatory building blocks. With the requirement of the CESE method in mind, a rigorous mathematical framework that clearly identities the reason behind the difficulties in use of such high-aspect ratio triangular/tetrahedral elements is presented here. As will be shown, it turns out that the degree of accuracy deterioration of gradient computation involving a triangular element is hinged on the value of its shape factor Gamma def = sq sin Alpha1 + sq sin Alpha2 + sq sin Alpha3, where Alpha1; Alpha2 and Alpha3 are the internal angles of the element. In fact, it is shown that the degree of accuracy deterioration increases monotonically as the value of Gamma decreases monotonically from its maximal value 9/4 (attained by an equilateral triangle only) to a value much less than 1 (associated with a highly obtuse triangle). By taking advantage of the fact that a high-aspect ratio triangle is not necessarily highly obtuse, and in fact it can have a shape factor whose value is close to the maximal value 9/4, a potential solution to avoid accuracy deterioration of gradient computation associated with a high-aspect ratio triangular grid is given. Also a brief discussion on the extension of the current mathematical framework to the

  6. Nexal membrane permeability to anions

    PubMed Central

    1978-01-01

    The permeability of the septa of the earthworm in the median axon has been calculated for the anions fluorescein and its halogen derivatives. The values ranged from 5.4 X 10(-5) to 4 X 10(-6) cm/s. Previously, the septa had been shown to contain nexuses. By using freeze-fracture material, the surface area of nexus on the septal membranes was determined to be 4.5%, very similar to the percentage of nexus in the intercalated disk of mammalian myocardium. Plasma membrane permeability to these dyes was also calculated and shown to be much less than that of the septal membranes. In addition, an estimate of cytoplasmic binding for each dye was made, and most dyes showed little or no binding with the exception of aminofluorescein. PMID:702107

  7. Solar Cell Materials by Design: Hybrid Pyroxene Corner-Sharing VO4 Tetrahedral Chains.

    PubMed

    El-Mellouhi, Fedwa; Akande, Akinlolu; Motta, Carlo; Rashkeev, Sergey N; Berdiyorov, Golibjon; Madjet, Mohamed El-Amine; Marzouk, Asma; Bentria, El Tayeb; Sanvito, Stefano; Kais, Sabre; Alharbi, Fahhad H

    2017-05-09

    Hybrid organic-inorganic frameworks provide numerous combinations of materials with a wide range of structural and electronic properties, which enable their use in various applications. In recent years, some of these hybrid materials-especially lead-based halide perovskites-have been successfully used for the development of highly efficient solar cells. The large variety of possible hybrid materials has inspired the search for other organic-inorganic frameworks that may exhibit enhanced performance over conventional lead halide perovskites. In this study, a new class of low-dimensional hybrid oxides for photovoltaic applications was developed by using electronic structure calculations in combination with analysis from existing materials databases, with a focus on vanadium oxide pyroxenes (tetrahedron-based frameworks), mainly due to their high stability and nontoxicity. Pyroxenes were screened with different cations [A] and detailed computational studies of their structural, electronic, optical and transport properties were performed. Low-dimensional hybrid vanadate pyroxenes [A]VO3 (with molecular cations [A] and corner-sharing VO4 tetrahedral chains) were found to satisfy all physical requirements needed to develop an efficient solar cell (a band gap of 1.0-1.7 eV, strong light absorption and good electron-transport properties). © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Multiple-Armed Tetrahedral DNA Nanostructures for Tumor-Targeting, Dual-Modality in Vivo Imaging.

    PubMed

    Jiang, Dawei; Sun, Yanhong; Li, Jiang; Li, Qian; Lv, Min; Zhu, Bing; Tian, Tian; Cheng, Dengfeng; Xia, Jiaoyun; Zhang, Lan; Wang, Lihua; Huang, Qing; Shi, Jiye; Fan, Chunhai

    2016-02-01

    In this work, we have developed multiple-armed DNA tetrahedral nanostructures (TDNs) for dual-modality in vivo imaging using near-infrared (NIR) fluorescence and single-photon emission computed tomography (SPECT). We found that the presence of arm strands in TDNs remarkably enhanced their in vitro stability, allowing them to stay intact for at least 12 h in serum. By using NIR fluorescence imaging, we evaluated in mice the pharmacokinetics of TDNs, which exhibited distinctly different in vivo biodistribution patterns compared with those of double-stranded (ds)DNA. We also noticed that TDNs had twofold longer circulation time in the blood system than that of dsDNA. With the use of multiple-armed TDNs, we could precisely anchor an exact number of functional groups including tumor-targeting folic acid (FA), NIR emitter Dylight 755, and radioactive isotope (99m)Tc on prescribed positions of TDNs, which showed the capability of targeted imaging ability in cancer cells. Furthermore, we realized noninvasive tumor-targeting imaging in tumor-bearing mice by using both NIR and SPECT modalities.

  9. A point-centered arbitrary Lagrangian Eulerian hydrodynamic approach for tetrahedral meshes

    DOE PAGES

    Morgan, Nathaniel R.; Waltz, Jacob I.; Burton, Donald E.; ...

    2015-02-24

    We present a three dimensional (3D) arbitrary Lagrangian Eulerian (ALE) hydrodynamic scheme suitable for modeling complex compressible flows on tetrahedral meshes. The new approach stores the conserved variables (mass, momentum, and total energy) at the nodes of the mesh and solves the conservation equations on a control volume surrounding the point. This type of an approach is termed a point-centered hydrodynamic (PCH) method. The conservation equations are discretized using an edge-based finite element (FE) approach with linear basis functions. All fluxes in the new approach are calculated at the center of each tetrahedron. A multidirectional Riemann-like problem is solved atmore » the center of the tetrahedron. The advective fluxes are calculated by solving a 1D Riemann problem on each face of the nodal control volume. A 2-stage Runge–Kutta method is used to evolve the solution forward in time, where the advective fluxes are part of the temporal integration. The mesh velocity is smoothed by solving a Laplacian equation. The details of the new ALE hydrodynamic scheme are discussed. Results from a range of numerical test problems are presented.« less

  10. Residual stress and Raman spectra of laser deposited highly-tetrahedral-coordinated-amorphous-carbon films

    SciTech Connect

    Friedmann, T.A.; Siegal, M.P.; Tallant, D.R.; Simpson, R.L.; Dominguez, F.

    1994-05-01

    We are studying carbon thin films by using a pulsed excimer laser to ablate pyrolytic graphite targets to form highly tetrahedral coordinated amorphous carbon ({alpha}t-C) films. These films have been grown on room temperature p-type Si (100) substrates without the intentional incorporation of hydrogen. In order to understand and optimize the growth of {alpha}t-C films, parametric studies of the growth parameters have been performed. We have also introduced various background gases (H{sub 2}, N{sub 2} and Ar) and varied the background gas pressure during deposition. The residual compressive stress levels in the films have been measured and correlated to changes in the Raman spectra of the {alpha}t-C band near 1565 cm{sup {minus}1}. The residual compressive stress falls with gas pressure, indicating a decreasing atomic sp{sup 3}-bonded carbon fraction. We find that reactive gases such as hydrogen and nitrogen significantly alter the Raman spectra at higher pressures. These effects are due to a combination of chemical incorporation of nitrogen and hydrogen into the film as well as collisional cooling of the ablation plume. In contrast, films grown in non-reactive Ar background gases show much less dramatic changes in the Raman spectra at similar pressures.

  11. Output-Adaptive Tetrahedral Cut-Cell Validation for Sonic Boom Prediction

    NASA Technical Reports Server (NTRS)

    Park, Michael A.; Darmofal, David L.

    2008-01-01

    A cut-cell approach to Computational Fluid Dynamics (CFD) that utilizes the median dual of a tetrahedral background grid is described. The discrete adjoint is also calculated, which permits adaptation based on improving the calculation of a specified output (off-body pressure signature) in supersonic inviscid flow. These predicted signatures are compared to wind tunnel measurements on and off the configuration centerline 10 body lengths below the model to validate the method for sonic boom prediction. Accurate mid-field sonic boom pressure signatures are calculated with the Euler equations without the use of hybrid grid or signature propagation methods. Highly-refined, shock-aligned anisotropic grids were produced by this method from coarse isotropic grids created without prior knowledge of shock locations. A heuristic reconstruction limiter provided stable flow and adjoint solution schemes while producing similar signatures to Barth-Jespersen and Venkatakrishnan limiters. The use of cut-cells with an output-based adaptive scheme completely automated this accurate prediction capability after a triangular mesh is generated for the cut surface. This automation drastically reduces the manual intervention required by existing methods.

  12. Erasing no-man's land by thermodynamically stabilizing the liquid-liquid transition in tetrahedral particles.

    PubMed

    Smallenburg, Frank; Filion, Laura; Sciortino, Francesco

    2014-09-01

    One of the most controversial hypotheses for explaining the origin of the thermodynamic anomalies characterizing liquid water postulates the presence of a metastable second-order liquid-liquid critical point [1] located in the "no-man's land" [2]. In this scenario, two liquids with distinct local structure emerge near the critical temperature. Unfortunately, since spontaneous crystallization is rapid in this region, experimental support for this hypothesis relies on significant extrapolations, either from the metastable liquid or from amorphous solid water [3, 4]. Although the liquid-liquid transition is expected to feature in many tetrahedrally coordinated liquids, including silicon [5], carbon [6] and silica, even numerical studies of atomic and molecular models have been unable to conclusively prove the existence of this transition. Here we provide such evidence for a model in which it is possible to continuously tune the softness of the interparticle interaction and the flexibility of the bonds, the key ingredients controlling the existence of the critical point. We show that conditions exist where the full coexistence is thermodynamically stable with respect to crystallization. Our work offers a basis for designing colloidal analogues of water exhibiting liquid-liquid transitions in equilibrium, opening the way for experimental confirmation of the original hypothesis.

  13. Non-Axial Octupole Deformations and Tetrahedral Symmetry in Heavy Nuclei

    SciTech Connect

    Mazurek, Katarzyna; Dudek, Jerzy

    2005-11-21

    The total energies of about 120 nuclei in the Thorium region have been calculated within the macroscopic-microscopic method in the 5-dimensional space of deformation parameters {alpha}20, {alpha}22, {alpha}30, {alpha}32 and {alpha}40. The macroscopic energy term contains the nuclear surface-curvature dependence as proposed within the LSD approach. The microscopic energies are calculated with the Woods-Saxon single particle potential employing the universal set of parameters.We study a possible presence of the octupole axial and non-axial degrees of freedom all-over in the ({beta}, {gamma})-plane focussing on the ground-states, secondary minima and in the saddle points. In fact, a competition between axial and tri-axial octupole deformation parameters is obtained at the saddle points and in the secondary minima for many isotones with N > 136. The presence of the tetrahedral symmetry minima is predicted in numerous nuclei in the discussed region, although most of the time at relatively high excitation energies.

  14. Heterogeneous Nucleation of an n-Alkane on Tetrahedrally Coordinated Crystals.

    PubMed

    Bourque, Alexander J; Locker, C Rebecca; Rutledge, Gregory C

    2017-02-02

    Heterogeneous nucleation refers to the propensity for phase transformations to initiate preferentially on foreign surfaces, such as vessel walls, dust particles, or formulation additives. In crystallization, the form of the initial nucleus has ramifications for the crystallographic form, morphology, and properties of the resulting solid. Nevertheless, the discovery and design of nucleating agents remains a matter of trial and error because of the very small spatiotemporal scales over which the critical nucleus is formed and the extreme difficulty of examining such events empirically. Using molecular dynamics simulations, we demonstrate a method for the rapid screening of entire families of materials for activity as nucleating agents and for characterizing their mechanism of action. The method is applied to the crystallization of n-pentacontane, a model surrogate for polyethylene, on the family of tetrahedrally coordinated crystals, including diamond and silicon. A systematic variation of parameters in the interaction potential permits a comprehensive, physically based screening of nucleating agents in this class of materials, including both real and hypothetical candidates. The induction time for heterogeneous nucleation is shown to depend strongly on crystallographic registry between the nucleating agent and the critical nucleus, indicative of an epitaxial mechanism in this class of materials. Importantly, the severity of this registry requirement weakens with decreasing rigidity of the substrate and increasing strength of attraction to the surface of the nucleating agent. Employing this method, a high-throughput computational screening of nucleating agents becomes possible, facilitating the discovery of novel nucleating agents within a broad "materials genome" of possible additives.

  15. Surface sites and unrelaxed surface energies of tetrahedral silica polymorphs and silicate

    NASA Astrophysics Data System (ADS)

    Murashov, Vladimir V.; Demchuk, Eugene

    2005-12-01

    Surface properties of respirable silica, which represents a major occupational safety concern, were investigated computationally, and a model for quantitative characterization of crystalline silica surface sites was developed. It was found that the surface energy of crystalline solids, such as silica and silicates, can be calculated as a product of the surface site density and site energy. The energies of sites formed by faceting tetrahedral silica polymorphs and aluminosilicate were determined by parametric fitting ab initio surface energies to site densities. Boltzmann's statistics was used to describe the distribution of faces as an exponential function of unrelaxed surface energy in the comminuted crystalline solids. Using these findings, crystallographic face distributions on fractured quartz, coesite, tridymite, and cristobalite were derived and average silanol hydroxyl densities in fractured particulate of these materials were estimated as 0.070, 0.059, 0.058, and 0.055 Å -2, respectively. The proposed method of quantitative characterization of the surface bridges the gap between microscopic simulations and measurable observables, such as cytotoxicity of respirable silica.

  16. ATS Scattering from the Tetrahedral and Octahedral Site in Magnetite and Franklinite

    NASA Astrophysics Data System (ADS)

    Kanazawa, Masayuki; Hagiwara, Kazunari; Kokubun, Jun; Ishida, Kohtaro

    2002-07-01

    The pre-edge peak as well as the main peak just above the Fe K-absorption edge is observed for anisotropic tensor of susceptibility (ATS) scattering in magnetite, Fe3O4 (inverse spinel structure). In order to investigate the origin of the peaks, we study the ATS scattering in franklinite, ZnFe2O4 (normal spinel structure) which has Zn atoms in the tetrahedral A sites and Fe atoms in the octahedral B sites. In franklinite, only the main ATS peak is observed at almost the same energy as magnetite. Therefore, the pre-edge and main peaks of magnetite originate from the A and B site atoms, respectively. Because the dipole transition of A site atoms cannot excite ATS scattering, the dipole-quadrupole transition is investigated. The observed energy spectra for the (002) and (006) reflections in magnetite reveal that the pre-edge peak is due to the dipole-quadrupole transition of Fe atoms in the A sites. Comparing the main peak intensities of both reflections in magnetite and franklinite, we conclude that the main peak in franklinite is caused by dipole transition of the B site atoms. However the contribution of dipole-quadrupole transition is presumed in magnetite.

  17. Tetrahedral DNA probe coupling with hybridization chain reaction for competitive thrombin aptasensor.

    PubMed

    Chen, Ying-Xu; Huang, Ke-Jing; He, Liu-Liu; Wang, Yi-Han

    2017-09-15

    A novel competitive aptasensor for thrombin detection is developed by using a tetrahedral DNA (T-DNA) probe and hybridization chain reaction (HCR) signal amplification. Sulfur and nitrogen co-doped reduced graphene oxide (SN-rGO) is firstly prepared by a simple reflux method and used for supporting substrate of biosensor. Then, T-DNA probe is modified on the electrode by Au-S bond and a competition is happened between target thrombin and the complementary DNA (cDNA) of aptamer. The aptamer binding to thrombin forms an aptamer-target conjugate and make the cDNA remained, and subsequently hybridizes with the vertical domain of T-DNA. Finally, the cDNAs trigger HCR, which results in a great current response by the catalysis of horseradish peroxidase to the hydrogen peroxide + hydroquinone system. For thrombin detection, the proposed biosensor shows a wide linearity range of 10(-13)-10(-8)M and a low detection limit of 11.6fM (S/N = 3), which is hopeful to apply in biotechnology and clinical diagnosis. Copyright © 2017 Elsevier B.V. All rights reserved.

  18. Occurrence and characterization of a tetrahedral nucleopolyhedrovirus from Spilarctia obliqua (Walker).

    PubMed

    Senthil Kumar, C M; Jacob, T K; Devasahayam, S; D'Silva, Sharon; Jinsha, J; Rajna, S

    2015-11-01

    Spilarctia obliqua Walker (Lepidoptera: Arctiidae) is a polyphagous insect pest damaging pulses, oil seeds, cereals, vegetables and medicinal and aromatic plants in India. The pest also infests turmeric and ginger sporadically in Kerala. We observed an epizootic caused by a nucleopolyhedrovirus (NPV) in field populations of the insects in December 2013. The NPV was purified and characterized. The isolate was tetrahedral in shape and belonged to multicapsid NPV. The REN profile of the SpobNPV genome with Pst I, Xho I and HindIII enzymes showed a genome size of 99.1±3.9 kbp. Partialpolh, lef-8 and lef-9 gene sequences of the isolate showed a close relationship with HycuNPV and SpphNPV. Phylogram and K-2-P distances between similar isolates suggested inclusion of the present SpobNPV isolate to group I NPV. The biological activity of the isolate was tested under laboratory conditions against third instar larvae of S. obliqua and the LC50 was 4.37×10(3)OBs/ml occlusion bodies (OBs) per ml. The median survival time (ST50) was 181 h at a dose of 1×10(6)OBs/ml and 167 h at a dose of 1×10(8)OBs/ml. SpobNPV merits further field evaluation as a potential biological control agent of S. obliqua, a serious pest of many agriculturally important crops in the Oriental region. Copyright © 2015 Elsevier Inc. All rights reserved.

  19. Collision-induced absorption in mixtures of symmetrical linear and tetrahedral molecules - Methane-nitrogen

    NASA Technical Reports Server (NTRS)

    Birnbaum, G.; Borysow, A.; Buechele, A.

    1993-01-01

    The far infrared absorption of a CH4-N2 mixture was measured at 297, 195, and 162 K from 30 to 650/cm. The spectral invariants gamma1 and alpha1, proportional, respectively, to the zeroth and first spectral moments, due to bimolecular collisions between CH4 and N2 were obtained from these data and compared with theoretical values. The theory for collision-induced dipoles between a tetrahedral and a diatomic or symmetrical linear molecule includes contributions not previously considered. Whereas the theoretical values of gamma1 are only somewhat greater than experiment at all temperatures, the theoretical values of alpha1 are significantly lower than the experimental values. From the theoretical spectral moments for the various induced dipole components, the parameters of the BC shape were computed, and theoretical spectra were constructed. Good agreement was obtained at the lower frequencies, but with increasing frequencies the theoretical spectra were increasingly less intense than the experimental spectra. Although the accuracy of the theoretical results may suffer from the lack of a reliable potential function, it does not appear that this high frequency discrepancy can be removed by any conceivable modification in the potential.

  20. Split-Cell, Linear Characteristic Transport Method for Unstructured Tetrahedral Meshes

    SciTech Connect

    Mathews, Kirk A.; Miller, Rodney L.; Brennan, Charles R.

    2000-10-15

    The linear characteristic (LC) method is extended to unstructured meshes of tetrahedral cells in three-dimensional Cartesian coordinates. For each ordinate in a discrete ordinates sweep, each cell is split into subcells along a line parallel to the ordinate. Direct affine transformations among appropriate oblique Cartesian coordinate systems for the faces and interior of each cell and subcell are used to simplify the characteristic transport through each subcell. This approach is straightforward and eliminates computationally expensive trigonometric functions. An efficient and well-conditioned technique for evaluating the required integral moments of exponential functions is presented. Various test problems are used to demonstrate (a) the approach to cubic convergence as the mesh is refined, (b) insensitivity to the details of irregular meshes, and (c) numerical robustness. These tests also show that meshes should represent volumes of regions with curved as well as planar boundaries exactly and that cells should have optical thicknesses throughout the mesh that are more or less equal. A hybrid Monte Carlo/discrete ordinates method, together with MCNP, is used to distinguish between error introduced by the angular and the spatial quadratures. We conclude that the LC method should be a practical and reliable scheme for these meshes, presuming that the cells are not optically too thick.

  1. Tetrahedral node for Transmission-Line Modeling (TLM) applied to Bio-heat Transfer.

    PubMed

    Milan, Hugo F M; Gebremedhin, Kifle G

    2016-12-01

    Transmission-Line Modeling (TLM) is a numerical method used to solve complex and time-domain bio-heat transfer problems. In TLM, parallelepipeds are used to discretize three-dimensional problems. The drawback in using parallelepiped shapes is that instead of refining only the domain of interest, a large additional domain would also have to be refined, which results in increased computational time and memory space. In this paper, we developed a tetrahedral node for TLM applied to bio-heat transfer that does not have the drawback associated with the parallelepiped node. The model includes heat source, blood perfusion, boundary conditions and initial conditions. The boundary conditions could be adiabatic, temperature, heat flux, or convection. The predicted temperature and heat flux were compared against results from an analytical solution and the results agreed within 2% for a mesh size of 69,941 nodes and a time step of 5ms. The method was further validated against published results of maximum skin-surface temperature difference in a breast with and without tumor and the results agreed within 6%. The published results were obtained from a model that used parallelepiped TLM node. An open source software, TLMBHT, was written using the theory developed herein and is available for download free-of-charge. Copyright © 2016 Elsevier Ltd. All rights reserved.

  2. A point-centered arbitrary Lagrangian Eulerian hydrodynamic approach for tetrahedral meshes

    SciTech Connect

    Morgan, Nathaniel R.; Waltz, Jacob I.; Burton, Donald E.; Charest, Marc R.; Canfield, Thomas R.; Wohlbier, John G.

    2015-02-24

    We present a three dimensional (3D) arbitrary Lagrangian Eulerian (ALE) hydrodynamic scheme suitable for modeling complex compressible flows on tetrahedral meshes. The new approach stores the conserved variables (mass, momentum, and total energy) at the nodes of the mesh and solves the conservation equations on a control volume surrounding the point. This type of an approach is termed a point-centered hydrodynamic (PCH) method. The conservation equations are discretized using an edge-based finite element (FE) approach with linear basis functions. All fluxes in the new approach are calculated at the center of each tetrahedron. A multidirectional Riemann-like problem is solved at the center of the tetrahedron. The advective fluxes are calculated by solving a 1D Riemann problem on each face of the nodal control volume. A 2-stage Runge–Kutta method is used to evolve the solution forward in time, where the advective fluxes are part of the temporal integration. The mesh velocity is smoothed by solving a Laplacian equation. The details of the new ALE hydrodynamic scheme are discussed. Results from a range of numerical test problems are presented.

  3. Aptamer-modified tetrahedral DNA nanostructure for tumor-targeted drug delivery.

    PubMed

    Li, Qianshun; Zhao, Dan; Shao, Xiaoru; Lin, Shiyu; Xie, Xueping; Liu, Mengting; Ma, Wenjuan; Shi, Sirong; Lin, Yunfeng

    2017-10-09

    Tetrahedral DNA nanostructures (TDNs) are considered promising drug delivery carriers because they are permeable to cellular membrane and biocompatible and biodegradable. Furthermore, they can be modified by functional groups. To improve the drug-delivering ability of TDNs, we chose anticancer aptamer AS1411 to modify TDNs for tumor-targeted drug delivery. AS1411 can specifically bind to nucleolin, which is overexpressed on the cell membrane of tumor cells. Furthermore, AS1411 can inhibit NF-κB signaling and reduce the expression of bcl-2. In this study, we compared the intracellular localization of AS1411-modified TDNs (Apt-TDNs) with that of TDNs in different cells under hypoxic condition. Furthermore, we compared the effects of Apt-TDNs and TDNs on cell growth and cell cycle under hypoxic condition. A substantial amount of Apt-TDNs entered and accumulated in the nucleus of MCF-7 cells; however, the amount of Apt-TDNs that entered L929 cells was comparatively less. TDNs entered in much less quantity in MCF-7 cells than Apt-TDNs. Moreover, there was little difference in the amount of TDNs that entered L929 cells and MCF-7 cells. Apt-TDNs can inhibit MCF-7 cell growth and promote L929 cell growth, while TDNs can promote both MCF-7 and L929 cell growth. Thus, the results indicate that Apt-TDNs are more effective tumor-targeted drug delivery vehicles than TDNs, with the ability to specifically inhibit tumor cell growth.

  4. Isosurface Computation Made Simple: Hardware acceleration,Adaptive Refinement and tetrahedral Stripping

    SciTech Connect

    Pascucci, V

    2004-02-18

    This paper presents a simple approach for rendering isosurfaces of a scalar field. Using the vertex programming capability of commodity graphics cards, we transfer the cost of computing an isosurface from the Central Processing Unit (CPU), running the main application, to the Graphics Processing Unit (GPU), rendering the images. We consider a tetrahedral decomposition of the domain and draw one quadrangle (quad) primitive per tetrahedron. A vertex program transforms the quad into the piece of isosurface within the tetrahedron (see Figure 2). In this way, the main application is only devoted to streaming the vertices of the tetrahedra from main memory to the graphics card. For adaptively refined rectilinear grids, the optimization of this streaming process leads to the definition of a new 3D space-filling curve, which generalizes the 2D Sierpinski curve used for efficient rendering of triangulated terrains. We maintain the simplicity of the scheme when constructing view-dependent adaptive refinements of the domain mesh. In particular, we guarantee the absence of T-junctions by satisfying local bounds in our nested error basis. The expensive stage of fixing cracks in the mesh is completely avoided. We discuss practical tradeoffs in the distribution of the workload between the application and the graphics hardware. With current GPU's it is convenient to perform certain computations on the main CPU. Beyond the performance considerations that will change with the new generations of GPU's this approach has the major advantage of avoiding completely the storage in memory of the isosurface vertices and triangles.

  5. Insights into Substrate Specificity and Metal Activation of Mammalian Tetrahedral Aspartyl Aminopeptidase*

    PubMed Central

    Chen, Yuanyuan; Farquhar, Erik R.; Chance, Mark R.; Palczewski, Krzysztof; Kiser, Philip D.

    2012-01-01

    Aminopeptidases are key enzymes involved in the regulation of signaling peptide activity. Here, we present a detailed biochemical and structural analysis of an evolutionary highly conserved aspartyl aminopeptidase called DNPEP. We show that this peptidase can cleave multiple physiologically relevant substrates, including angiotensins, and thus may play a key role in regulating neuron function. Using a combination of x-ray crystallography, x-ray absorption spectroscopy, and single particle electron microscopy analysis, we provide the first detailed structural analysis of DNPEP. We show that this enzyme possesses a binuclear zinc-active site in which one of the zinc ions is readily exchangeable with other divalent cations such as manganese, which strongly stimulates the enzymatic activity of the protein. The plasticity of this metal-binding site suggests a mechanism for regulation of DNPEP activity. We also demonstrate that DNPEP assembles into a functionally relevant tetrahedral complex that restricts access of peptide substrates to the active site. These structural data allow rationalization of the enzyme's preference for short peptide substrates with N-terminal acidic residues. This study provides a structural basis for understanding the physiology and bioinorganic chemistry of DNPEP and other M18 family aminopeptidases. PMID:22356908

  6. Earliest stage of the tetrahedral nanochannel formation in cubosome particles from unilamellar nanovesicles.

    PubMed

    Angelov, Borislav; Angelova, Angelina; Garamus, Vasil M; Drechsler, Markus; Willumeit, Regine; Mutafchieva, Rada; Štěpánek, Petr; Lesieur, Sylviane

    2012-12-04

    Studies of nonequilibrium lipid polymorphism at the nanoscale contribute to the in-depth understanding of the structural pathways for formation of aqueous channels and emerging of channels-network ordering in liquid-crystalline (LC) nanovehicles. We present experimental structural evidence for the smallest tetrahedral-type lipid membrane aggregate, which involves completely formed nanochannels and occurs as an early intermediate state during the bilayer vesicle-to-cubosome particle transition. Nanovehicles are generated from a self-assembled lipid mixture and studied by means of high-resolution cryogenic transmission electron microscopy (cryo-TEM) and synchrotron radiation small-angle X-ray scattering (SAXS). The investigated lipid membrane composition allows for the stabilization of long-lived intermediates throughout the unilamellar vesicle-to-cubosome nanoparticle (NP) transformation at ambient temperature. The observed small cubosomic particles, with well-defined water channels, appear to be precursors of larger cubic membrane structures, thus confirming the theoretical modeling of nanochannel-network growth in diamond-type cubic lipid particles. The reported structural findings, highlighting that bilayer vesicle membrane packing and fusion are required for nanochanneled cubosome particle formation, are anticipated to advance the engineering of small lipid NPs with controllable channels for biomolecular loading and release.

  7. Correlation between substrate bias, growth process and structural properties of phosphorus incorporated tetrahedral amorphous carbon films

    NASA Astrophysics Data System (ADS)

    Liu, Aiping; Zhu, Jiaqi; Han, Jiecai; Wu, Huaping; Jia, Zechun

    2007-09-01

    We investigate the growth process and structural properties of phosphorus incorporated tetrahedral amorphous carbon (ta-C:P) films which are deposited at different substrate biases by filtered cathodic vacuum arc technique with PH 3 as the dopant source. The films are characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy, Raman spectroscopy, residual stress measurement, UV/VIS/NIR absorption spectroscopy and temperature-dependent conductivity measurement. The atomic fraction of phosphorus in the films as a function of substrate bias is obtained by XPS analysis. The optimum bias for phosphorus incorporation is about -80 V. Raman spectra show that the amorphous structures of all samples with atomic-scaled smooth surface are not remarkably changed when PH 3 is implanted, but some small graphitic crystallites are formed. Moreover, phosphorus impurities and higher-energetic impinging ions are favorable for the clustering of sp 2 sites dispersed in sp 3 skeleton and increase the level of structural ordering for ta-C:P films, which further releases the compressive stress and enhances the conductivity of the films. Our analysis establishes an interrelationship between microstructure, stress state, electrical properties, and substrate bias, which helps to understand the deposition mechanism of ta-C:P films.

  8. Insights into Substrate Specificity and Metal Activation of Mammalian Tetrahedral Aspartyl Aminopeptidase

    SciTech Connect

    Chen, Yuanyuan; Farquhar, Erik R.; Chance, Mark R.; Palczewski, Krzysztof; Kiser, Philip D.

    2012-07-11

    Aminopeptidases are key enzymes involved in the regulation of signaling peptide activity. Here, we present a detailed biochemical and structural analysis of an evolutionary highly conserved aspartyl aminopeptidase called DNPEP. We show that this peptidase can cleave multiple physiologically relevant substrates, including angiotensins, and thus may play a key role in regulating neuron function. Using a combination of x-ray crystallography, x-ray absorption spectroscopy, and single particle electron microscopy analysis, we provide the first detailed structural analysis of DNPEP. We show that this enzyme possesses a binuclear zinc-active site in which one of the zinc ions is readily exchangeable with other divalent cations such as manganese, which strongly stimulates the enzymatic activity of the protein. The plasticity of this metal-binding site suggests a mechanism for regulation of DNPEP activity. We also demonstrate that DNPEP assembles into a functionally relevant tetrahedral complex that restricts access of peptide substrates to the active site. These structural data allow rationalization of the enzyme's preference for short peptide substrates with N-terminal acidic residues. This study provides a structural basis for understanding the physiology and bioinorganic chemistry of DNPEP and other M18 family aminopeptidases.

  9. A spherical hohlraum design with tetrahedral 4 laser entrance holes and high radiation performance

    NASA Astrophysics Data System (ADS)

    Jiang, Shaoen; Jing, Longfei; Huang, Yunbao; Li, Haiyan; Huang, Tianxuan; Ding, Yongkun

    2016-12-01

    As usual cylindrical hohlraum with double laser ring cones may lead to serious laser-plasma interaction, such as the simulated Raman scatter and cross-beam energy transfer effect, spherical hohlraum with octahedral 6 Laser Entrance Holes (LEHs) and single cone laser beams, was investigated and reported to have a consistent high radiation symmetry during the whole implosion process. However, it has several potential challenges such as the smaller space left for diagnosis and the assembly of centrally located capsule. In this paper, based on the view-factor model, we investigate the radiation symmetry and the drive temperature on the capsule located in the spherical hohlraum with tetrahedral 4 LEHs and single cone laser beams, since there is more available space for laser disposition and diagnosis. Then, such target is optimized on the laser beam pointing direction to achieve a high radiation performance, i.e., the radiation symmetry and drive temperature on the capsule. Finally, an optimal spherical hohlraum with optimal laser beam pointing has been demonstrated and compared with the spherical hohlraum with octahedral 6 LEHs. The resulting radiation symmetry and the drive temperature shows that it has almost a similar radiation symmetry (the radiation asymmetry variation is no more than 0.2%), and higher drive temperature (the temperature has been increased by 1.73%, and an additional 133 kJ energy of 2 MJ energy for fusion can be saved).

  10. A Novel Spherical Hohlraum Design with Tetrahedral 4 Laser Entrance Holes and High Radiation Performance

    NASA Astrophysics Data System (ADS)

    Jing, Longfei; Huang, Yunbao; Jiang, Shaoen; Li, Haiyan; Huang, Tianxuan; Ding, Yongkun

    2016-10-01

    As usual cylindrical hohlraum with double laser ring cones may lead to serious CBET effect, spherical hohlraum with octahedral 6 LEHs and single laser ring cone is presented to achieve higher radiation symmetry during the fusion process. However, it has several potential problems such as the long run distance, smaller space is left for diagnose, and the assembly of centrally located capsule. In this paper, we investigate the radiation performance, i.e., radiation symmetry and drive temperature on the capsule in the spherical hohlraum with tetrahedral 4 LEHs and single laser ring cone, since there is more available space for laser disposition and diagnose. Then, such target is optimized on the laser beam pointing direction and shape sizes to achieve high radiation performance, or the radiation symmetry and drive temperature on the capsule. Finally, a novel spherical hohlraum with optimal laser beam pointing and shape size has been demonstrated to have almost similar radiation symmetry (the radiation asymmetry variation is no more than 0.2%), and higher drive temperature (the temperature has been increased by 1.73%, and additional 133 KJ energy of 2MJ energy for fusion can be utilized).. This work was supportedby NSAF#U1430124, and NSFC#51375185, #51405177, #11475154.

  11. A Novel Spherical Hohlraum Design with Tetrahedral 4 Laser Entrance Holes and High Radiation Performance

    NASA Astrophysics Data System (ADS)

    Huang, Yunbao; Jing, Longfei; Jiang, Shaoen

    2016-10-01

    As usual cylindrical hohlraum with double laser ring cones may lead to serious CBET, and LPI effect, spherical hohlraum with octahedral 6 LEHs and single laser ring cone is investigated and presented to achieve higher radiation symmetry during the fusion process. However, it has several potential problems such as the long run distance and the close distance between the spot and their closet LEH for the laser beams, smaller space is left for diagnose, and the assembly of centrally located capsule. In this paper, based on view-factor transportation model, we investigate the radiation symmetry and the drive temperature on the centrally located capsule in the spherical hohlraum with tetrahedral 4 LEHs and single laser ring cone, since there is more available space for laser disposition and diagnose. Then, such target is optimized on the laser beam pointing direction and shape sizes to achieve high radiation performance, or the radiation symmetry and drive temperature on the capsule. Finally, a novel spherical hohlraum with optimal laser beam pointing and shape size has been demonstrated to have almost similar radiation symmetry (the radiation asymmetry variation is no more than 0.2%), and higher drive temperature (the temperature has been increased by 1.73%, and additional 133 KJ energy of 2MJ energy for fusion can be utilized).

  12. Collision-induced absorption in mixtures of symmetrical linear and tetrahedral molecules - Methane-nitrogen

    NASA Technical Reports Server (NTRS)

    Birnbaum, G.; Borysow, A.; Buechele, A.

    1993-01-01

    The far infrared absorption of a CH4-N2 mixture was measured at 297, 195, and 162 K from 30 to 650/cm. The spectral invariants gamma1 and alpha1, proportional, respectively, to the zeroth and first spectral moments, due to bimolecular collisions between CH4 and N2 were obtained from these data and compared with theoretical values. The theory for collision-induced dipoles between a tetrahedral and a diatomic or symmetrical linear molecule includes contributions not previously considered. Whereas the theoretical values of gamma1 are only somewhat greater than experiment at all temperatures, the theoretical values of alpha1 are significantly lower than the experimental values. From the theoretical spectral moments for the various induced dipole components, the parameters of the BC shape were computed, and theoretical spectra were constructed. Good agreement was obtained at the lower frequencies, but with increasing frequencies the theoretical spectra were increasingly less intense than the experimental spectra. Although the accuracy of the theoretical results may suffer from the lack of a reliable potential function, it does not appear that this high frequency discrepancy can be removed by any conceivable modification in the potential.

  13. Pickering emulsion templated interfacial atom transfer radical polymerization for microencapsulation.

    PubMed

    Li, Jian; Hitchcock, Adam P; Stöver, Harald D H

    2010-12-07

    This Article describes a new microencapsulation method based on a Pickering emulsion templated interfacial atom transfer radical polymerization (PETI-ATRP). Cationic LUDOX CL nanoparticles were coated electrostatically with an anionic polymeric ATRP initiator, poly(sodium styrene sulfonate-co-2-(2-bromoisobutyryloxy)ethyl methacrylate) (PSB), prepared by radical copolymerization of sodium styrene sulfonate and 2-(2-bromoisobutyryloxy)ethyl methacrylate (BIEM). The resulting PSB-modified CL particles were surface active and could be used to stabilize oil-in-water Pickering emulsions. ATRP of water-soluble cross-linking monomers, confined to the oil-water interface by the surface-bound PSB, then led to nanoparticle/polymer composite shells. This method allowed encapsulation of core solvents (xylene, hexadecane, perfluoroheptane) with different solubility parameters. The microcapsule (MC) wall chemistry could accommodate different monomers, demonstrating the versatility of this method. Double-walled MCs were formed by sequentially carrying out PETI-ATRP and in situ polymerization of encapsulated monomers. The double-walled structure was verified by both transmission electron microscopy (TEM) and scanning transmission X-ray microscopy (STXM).

  14. Tripodal Receptors for Cation and Anion Sensors

    PubMed Central

    Kuswandi, Bambang; Nuriman; Verboom, Willem; Reinhoudt, David N.

    2006-01-01

    This review discusses different types of artificial tripodal receptors for the selective recognition and sensing of cations and anions. Examples on the relationship between structure and selectivity towards cations and anions are described. Furthermore, their applications as potentiometric ion sensing are emphasised, along with their potential applications in optical sensors or optodes.

  15. Kinetics of silica polymerization

    SciTech Connect

    Weres, O.; Yee, A.; Tsao, L.

    1980-05-01

    The polymerization of silicic acid in geothermal brine-like aqueous solutions to produce amorphous silica in colloidal form has been studied experimentally and theoretically. A large amount of high quality experimental data has been generated over the temperature rang 23 to 100{sup 0}C. Wide ranges of dissolved silica concentration, pH, and sodium chloride concentration were covered. The catalytic effects of fluoride and the reaction inhibiting effects of aluminum and boron were studied also. Two basic processes have been separately studied: the formation of new colloidal particles by the homogeneous nucleation process and the deposition of dissolved silica on pre-existing colloidal particles. A rigorous theory of the formation of colloidal particles of amorphous silica by homogeneous nucleation was developed. This theory employs the Lothe-Pound formalism, and is embodied in the computer code SILNUC which quantitatively models the homogeneous nucleation and growth of colloidal silica particles in more than enough detail for practical application. The theory and code were extensively used in planning the experimental work and analyzing the data produced. The code is now complete and running in its final form. It is capable of reproducing most of the experimental results to within experimental error. It is also capable of extrapolation to experimentally inaccessible conditions, i.e., high temperatures, rapidly varying temperature and pH, etc.

  16. Direct polymerization of proteins.

    PubMed

    Albayrak, Cem; Swartz, James R

    2014-06-20

    We report the synthesis of active polymers of superfolder green fluorescent protein (sfGFP) in one step using Click chemistry. Up to six copies of the non-natural amino acids (nnAAs) p-azido-l-phenylalanine (pAzF) or p-propargyloxy-l-phenylalanine (pPaF) were site-specifically inserted into sfGFP by cell-free protein synthesis (CFPS). sfGFP containing two or three copies of these nnAAs were coupled by copper-catalyzed azide-alkyne cycloaddition to synthesize linear or branched protein polymers, respectively. The protein polymers retained ≥63% of their specific activity (i.e., fluorescence) after coupling. Polymerization of a concentrated solution of triply substituted sfGFP resulted in fluorescent macromolecular particles. Our method can be generalized to synthesize polymers of a protein or copolymers of any two or more proteins, and the conjugation sites can be determined exactly by standard genetic manipulation. Polymers of proteins and small molecules can also be created with this technology to make a new class of scaffolds or biomaterials.

  17. Synthesis of Novel Hydrocarbon Soluble Multifunctional Anionic Initiators: Tools for Synthesis of Novel Dendrimer and Molecular Brush Polymer Architectures

    DTIC Science & Technology

    2015-02-09

    bearing bulky substituents and separated through ether or ethylene oxide linkages. Such a strategy should minimize aggregation and improve... ethylene oxide bridge at the meta- position of every DPE unit in the core molecule (Scheme 1). This imparts flexibility around the spacer and avoids...for anionic polymerization. The complete synthesis of the unsaturated tri-Diphenylethylene compound 4,4,4-(ethane-1,1,1-triyl)tris(((3-(1-phenylvinyl

  18. Anion-π Catalysis on Fullerenes.

    PubMed

    López-Andarias, Javier; Frontera, Antonio; Matile, Stefan

    2017-09-13

    Anion-π interactions on fullerenes are about as poorly explored as the use of fullerenes in catalysis. However, strong exchange-correlation contributions and the localized π holes on their surface promise unique selectivities. To elaborate on this promise, tertiary amines are attached nearby. Dependent on their positioning, the resulting stabilization of anionic transition states on fullerenes is shown to accelerate disfavored enolate addition and exo Diels-Alder reactions enantioselectively. The found selectivities are consistent with computational simulations, particularly concerning the discrimination of differently planarized and charge-delocalized enolate tautomers by anion-π interactions. Enolate-π interactions on fullerenes are much shorter than standard π-π interactions and anion-π interactions on planar surfaces, and alternative cation-π interactions are not observed. These findings open new perspectives with regard to anion-π interactions in general and the use of carbon allotropes in catalysis.

  19. Creating molecular macrocycles for anion recognition

    PubMed Central

    2016-01-01

    Summary The creation and functionality of new classes of macrocycles that are shape persistent and can bind anions is described. The genesis of triazolophane macrocycles emerges out of activity surrounding 1,2,3-triazoles made using click chemistry; and the same triazoles are responsible for anion capture. Mistakes made and lessons learnt in anion recognition provide deeper understanding that, together with theory, now provides for computer-aided receptor design. The lessons are acted upon in the creation of two new macrocycles. First, cyanostars are larger and like to capture large anions. Second is tricarb, which also favors large anions but shows a propensity to self-assemble in an orderly and stable manner, laying a foundation for future designs of hierarchical nanostructures. PMID:27340452

  20. Asymmetric Anion-π Catalysis on Perylenediimides.

    PubMed

    Wang, Chao; Miros, François N; Mareda, Jiri; Sakai, Naomi; Matile, Stefan

    2016-11-07

    Anion-π catalysis, that is the stabilization of anionic transition states on π-acidic aromatic surfaces, has so far been developed with naphthalenediimides (NDIs). This report introduces perylenediimides (PDIs) to anion-π catalysis. The quadrupole moment of PDIs (+23.2 B) is found to exceed that of NDIs and reach new records with acceptors in the core (+70.9 B), and their larger surface provides space to better accommodate chemical transformations. Unlike NDIs, the activity of PDI catalysts for enolate and enamine addition is determined by the twist of their π surface rather than their reducibility. These results, further strengthened by nitrate inhibition and circular dichroism spectroscopy, support an understanding of anion-π interactions centered around quadrupole moments, i.e., electrostatic contributions, rather than redox potentials and charge transfer. The large PDI surfaces provide access to the highest enantioselectivities observed so far in anion-π catalysis (96 % ee).

  1. Closing the gap on unmeasured anions

    PubMed Central

    Kellum, John A

    2003-01-01

    Many critically ill and injured patients, especially those with metabolic acidosis, have abnormally high levels of unmeasured anions in their blood. At the same time, such patients are prone to hypoalbuminemia, which makes the traditional anion gap calculation inaccurate. Thus, little is known about the epidemiology and clinical consequences of an excess in unmeasured anions in the blood. Indeed, even the etiology of these "missing ions" is often unclear. Unfortunately, more precise means of quantifying unmeasured anions, such as the strong ion gap (SIG), are cumbersome to use clinically. However, a simple means of correcting the anion gap can be used to estimate SIG and may provide additional insight into this common clinical problem. PMID:12793870

  2. High-pressure polymeric phases of carbon dioxide.

    PubMed

    Sun, Jian; Klug, Dennis D; Martonák, Roman; Montoya, Javier Antonio; Lee, Mal-Soon; Scandolo, Sandro; Tosatti, Erio

    2009-04-14

    Understanding the structural transformations of solid CO(2) from a molecular solid characterized by weak intermolecular bonding to a 3-dimensional network solid at high pressure has challenged researchers for the past decade. We employ the recently developed metadynamics method combined with ab initio calculations to provide fundamental insight into recent experimental reports on carbon dioxide in the 60-80 GPa pressure region. Pressure-induced polymeric phases and their transformation mechanisms are found. Metadynamics simulations starting from the CO(2)-II (P4(2)/mnm) at 60 GPa and 600 K proceed via an intermediate, partially polymerized phase, and finally yield a fully tetrahedral, layered structure (P-4m2). Based on the agreement between calculated and experimental Raman and X-ray patterns, the recently identified phase VI [Iota V, et al. (2007) Sixfold coordinated carbon dioxide VI. Nature Mat 6:34-38], assumed to be disordered stishovite-like, is instead interpreted as the result of an incomplete transformation of the molecular phase into a final layered structure. In addition, an alpha-cristobalite-like structure (P4(1)2(1)2), is predicted to be formed from CO(2)-III (Cmca) via an intermediate Pbca structure at 80 GPa and low temperatures (<300 K). Defects in the crystals are frequently observed in the calculations at 300 K whereas at 500 to 700 K, CO(2)-III transforms to an amorphous form, consistent with experiment [Santoro M, et al. (2006) Amorphous silica-like carbon dioxide. Nature 441:857-860], but the simulation yields additional structural details for this disordered solid.

  3. High-pressure polymeric phases of carbon dioxide

    PubMed Central

    Sun, Jian; Klug, Dennis D.; Martoňák, Roman; Montoya, Javier Antonio; Lee, Mal-Soon; Scandolo, Sandro; Tosatti, Erio

    2009-01-01

    Understanding the structural transformations of solid CO2 from a molecular solid characterized by weak intermolecular bonding to a 3-dimensional network solid at high pressure has challenged researchers for the past decade. We employ the recently developed metadynamics method combined with ab initio calculations to provide fundamental insight into recent experimental reports on carbon dioxide in the 60–80 GPa pressure region. Pressure-induced polymeric phases and their transformation mechanisms are found. Metadynamics simulations starting from the CO2-II (P42/mnm) at 60 GPa and 600 K proceed via an intermediate, partially polymerized phase, and finally yield a fully tetrahedral, layered structure (P-4m2). Based on the agreement between calculated and experimental Raman and X-ray patterns, the recently identified phase VI [Iota V, et al. (2007) Sixfold coordinated carbon dioxide VI. Nature Mat 6:34–38], assumed to be disordered stishovite-like, is instead interpreted as the result of an incomplete transformation of the molecular phase into a final layered structure. In addition, an α-cristobalite-like structure (P41212), is predicted to be formed from CO2-III (Cmca) via an intermediate Pbca structure at 80 GPa and low temperatures (<300 K). Defects in the crystals are frequently observed in the calculations at 300 K whereas at 500 to 700 K, CO2-III transforms to an amorphous form, consistent with experiment [Santoro M, et al. (2006) Amorphous silica-like carbon dioxide. Nature 441:857–860], but the simulation yields additional structural details for this disordered solid. PMID:19332796

  4. Metastable Polymeric Nitrogen: The Ultimate Green High-Energy-Density Material

    NASA Astrophysics Data System (ADS)

    Ciezak, Jennifer

    2007-06-01

    High-energy-high-density materials offering increased stability, vulnerability, and environmental safety are being aggressively pursued to meet the requirements of the DoD Joint Visions and Future Force. Nearly two decades ago, it was proposed that polymeric nitrogen would exceed all of these requirements and possess nearly five times the energy of any conventional energetic material in use today. The present study details an investigation into nitrogen polymerization using a novel high-pressure approach utilizing sodium azide as the starting material. Due to the weaker bonding structure of the anionic azide chains in comparison to a N-N triple bond, one expects that the azide chains will create single-covalently bonded polymeric networks more easily than diatomic nitrogen. A polymeric form of sodium azide was synthesized at high pressures, but the material was not metastable at ambient conditions, which precluded performance testing. Quantum chemical calculations have indicated stabilization of the polymeric structure at ambient conditions may be possible with the addition of hydrogen. Vibrational spectroscopic characterization suggests that a meta-stable polymeric form of nitrogen has been synthesized under high-pressure using sodium azide/hydrogen as the starting materials. This material remains stable at ambient conditions upwards of two weeks depending on the storage conditions.

  5. Polymerization of Ethylene Oxide, Propylene Oxide, and Other Alkylene Oxides: Synthesis, Novel Polymer Architectures, and Bioconjugation.

    PubMed

    Herzberger, Jana; Niederer, Kerstin; Pohlit, Hannah; Seiwert, Jan; Worm, Matthias; Wurm, Frederik R; Frey, Holger

    2016-02-24

    The review summarizes current trends and developments in the polymerization of alkylene oxides in the last two decades since 1995, with a particular focus on the most important epoxide monomers ethylene oxide (EO), propylene oxide (PO), and butylene oxide (BO). Classical synthetic pathways, i.e., anionic polymerization, coordination polymerization, and cationic polymerization of epoxides (oxiranes), are briefly reviewed. The main focus of the review lies on more recent and in some cases metal-free methods for epoxide polymerization, i.e., the activated monomer strategy, the use of organocatalysts, such as N-heterocyclic carbenes (NHCs) and N-heterocyclic olefins (NHOs) as well as phosphazene bases. In addition, the commercially relevant double-metal cyanide (DMC) catalyst systems are discussed. Besides the synthetic progress, new types of multifunctional linear PEG (mf-PEG) and PPO structures accessible by copolymerization of EO or PO with functional epoxide comonomers are presented as well as complex branched, hyperbranched, and dendrimer like polyethers. Amphiphilic block copolymers based on PEO and PPO (Poloxamers and Pluronics) and advances in the area of PEGylation as the most important bioconjugation strategy are also summarized. With the ever growing toolbox for epoxide polymerization, a "polyether universe" may be envisaged that in its structural diversity parallels the immense variety of structural options available for polymers based on vinyl monomers with a purely carbon-based backbone.

  6. Anion stripping as a general method to create cationic porous framework with mobile anions.

    PubMed

    Mao, Chengyu; Kudla, Ryan A; Zuo, Fan; Zhao, Xiang; Mueller, Leonard J; Bu, Xianhui; Feng, Pingyun

    2014-05-28

    Metal-organic frameworks (MOFs) with cationic frameworks and mobile anions have many applications from sensing, anion exchange and separation, to fast ion conductivity. Despite recent progress, the vast majority of MOFs have neutral frameworks. A common mechanism for the formation of neutral frameworks is the attachment of anionic species such as F(-) or OH(-) to the framework metal sites, neutralizing an otherwise cationic scaffolding. Here, we report a general method capable of converting such neutral frameworks directly into cationic ones with concurrent generation of mobile anions. Our method is based on the differential affinity between distinct metal ions with framework anionic species. Specifically, Al(3+) is used to strip F(-) anions away from framework Cr(3+) sites, leading to cationic frameworks with mobile Cl(-) anions. The subsequent anion exchange with OH(-) further leads to a porous network with mobile OH(-) anions. New materials prepared by anion stripping can undergo ion exchange with anionic organic dyes and also exhibit much improved ionic conductivity compared to the original unmodified MOFs.

  7. Polymerized supramolecular assemblies and biocompatibility

    NASA Astrophysics Data System (ADS)

    O'Brien, David F.

    2001-03-01

    The creation of durable, biomembrane-mimetic coatings for inorganic and polymeric surfaces that are biocompatible, i.e. resistant to nonspecific protein adsorption, remains an important goal that is expected to impact numerous fields. It has already been shown that the physical stability of lipid bilayer vesicles can be dramatically enhanced by cross-linking polymerization of reactive lipids, such as phosphatidylcholines. Bilayers of these same lipids on clean silicon dioxide surfaces can be formed by fusion of small bilayer vesicles with the surface. Radical initiated polymerization of these supported bilayers yields a stable poly(lipid) film that is not perturbed upon exposure to surfactant. Moreover, the cross-linked bilayer film can be removed from water into air with retention of the poly(lipid) bilayer structure. These polymerized bilayer films could be repeatedly transferred from water to air to water with no obvious change in their biocompatibility. The supported bilayer films were equally resistant to non-specific protein adsorption before and after polymerization. This indicates that biocompatible nature of the phosphorylcholine head group of the lipids was not compromised by polymerization of the lipids. The ability to maintain surface biocompatibility of membranes while substantially increasing their stability would appear to extend the technological uses of supramolecular assemblies of lipids.

  8. Efficient calculation of the quasi-static electrical potential on a tetrahedral mesh and its implementation in STEPS

    PubMed Central

    Hepburn, Iain; Cannon, Robert; De Schutter, Erik

    2013-01-01

    We describe a novel method for calculating the quasi-static electrical potential on tetrahedral meshes, which we call E-Field. The E-Field method is implemented in STEPS, which performs stochastic spatial reaction-diffusion computations in tetrahedral-based cellular geometry reconstructions. This provides a level of integration between electrical excitability and spatial molecular dynamics in realistic cellular morphology not previously achievable. Deterministic solutions are also possible. By performing the Rallpack tests we demonstrate the accuracy of the E-Field method. Efficient node ordering is an important practical consideration, and we find that a breadth-first search provides the best solutions, although principal axis ordering suffices for some geometries. We discuss potential applications and possible future directions, and predict that the E-Field implementation in STEPS will play an important role in the future of multiscale neural simulations. PMID:24194715

  9. Development of a fully automated CFD system for three-dimensional flow simulations based on hybrid prismatic-tetrahedral grids

    SciTech Connect

    Berg, J.W. van der; Maseland, J.E.J.; Oskam, B.

    1996-12-31

    In this paper an assessment of CFD methods based on the underlying grid type is made. It is safe to say that emerging CFD methods based on hybrid body-fitted grids of tetrahedral and prismatic cells using unstructured data storage schemes have the potential to satisfy the basic requirements of problem-turnaround-time and accuracy for complex geometries. The CFD system described in this paper is based on the hybrid prismatic-tetrahedral grid approach. In an analysis it is shown that the cells in the prismatic layer have to satisfy a central symmetry property in order to obtain a second-order accurate approximation of the viscous terms in the Reynolds-averaged Navier-Stokes equations. Prismatic grid generation is demonstrated for the ONERA M6 wing-alone configuration and the AS28G wing/body configuration.

  10. Efficient calculation of the quasi-static electrical potential on a tetrahedral mesh and its implementation in STEPS.

    PubMed

    Hepburn, Iain; Cannon, Robert; De Schutter, Erik

    2013-01-01

    We describe a novel method for calculating the quasi-static electrical potential on tetrahedral meshes, which we call E-Field. The E-Field method is implemented in STEPS, which performs stochastic spatial reaction-diffusion computations in tetrahedral-based cellular geometry reconstructions. This provides a level of integration between electrical excitability and spatial molecular dynamics in realistic cellular morphology not previously achievable. Deterministic solutions are also possible. By performing the Rallpack tests we demonstrate the accuracy of the E-Field method. Efficient node ordering is an important practical consideration, and we find that a breadth-first search provides the best solutions, although principal axis ordering suffices for some geometries. We discuss potential applications and possible future directions, and predict that the E-Field implementation in STEPS will play an important role in the future of multiscale neural simulations.

  11. Synthesis of tetrahedral quasi-type-II CdSe-CdS core-shell quantum dots.

    PubMed

    Sugunan, Abhilash; Zhao, Yichen; Mitra, Somak; Dong, Lin; Li, Shanghua; Popov, Sergei; Marcinkevicius, Saulius; Toprak, Muhammet S; Muhammed, Mamoun

    2011-10-21

    Synthesis of colloidal nanocrystals of II-VI semiconductor materials has been refined in recent decades and their size dependent optoelectronic properties have been well established. Here we report a facile synthesis of CdSe-CdS core-shell heterostructures using a two-step hot injection process. Red-shifts in absorption and photoluminescence spectra show that the obtained quantum dots have quasi-type-II alignment of energy levels. The obtained nanocrystals have a heterostructure with a large and highly faceted tetrahedral CdS shell grown epitaxially over a spherical CdSe core. The obtained morphology as well as high resolution electron microscopy confirms that the tetrahedral shell have a zinc blende crystal structure. A phenomenological mechanism for the growth and morphology of the nanocrystals is discussed.

  12. Cytosine Nucleobase Ligand: A Suitable Choice for Modulating Magnetic Anisotropy in Tetrahedrally Coordinated Mononuclear Co(II) Compounds.

    PubMed

    Bruno, Rosaria; Vallejo, Julia; Marino, Nadia; De Munno, Giovanni; Krzystek, J; Cano, Joan; Pardo, Emilio; Armentano, Donatella

    2017-02-20

    A family of tetrahedral mononuclear Co(II) complexes with the cytosine nucleobase ligand is used as the playground for an in-depth study of the effects that the nature of the ligand, as well as their noninnocent distortions on the Co(II) environment, may have on the slow magnetic relaxation effects. Hence, those compounds with greater distortion from the ideal tetrahedral geometry showed a larger-magnitude axial magnetic anisotropy (D) together with a high rhombicity factor (E/D), and thus, slow magnetic relaxation effects also appear. In turn, the more symmetric compound possesses a much smaller value of the D parameter and, consequently, lacks single-ion magnet behavior.

  13. Synthesis, structural elucidation, and catalytic properties in olefin epoxidation of the polymeric hybrid material [Mo3O9(2-[3(5)-pyrazolyl]pyridine)]n.

    PubMed

    Amarante, Tatiana R; Neves, Patrícia; Gomes, Ana C; Nolasco, Mariela M; Ribeiro-Claro, Paulo; Coelho, Ana C; Valente, Anabela A; Paz, Filipe A Almeida; Smeets, Stef; McCusker, Lynne B; Pillinger, Martyn; Gonçalves, Isabel S

    2014-03-03

    The reaction of [MoO2Cl2(pzpy)] (1) (pzpy = 2-[3(5)-pyrazolyl]pyridine) with water in an open reflux system (16 h), in a microwave synthesis system (120 °C, 2 h), or in a Teflon-lined stainless steel digestion bomb (100 °C, 19 h) gave the molybdenum oxide/pyrazolylpyridine polymeric hybrid material [Mo3O9(pzpy)]n (2) as a microcrystalline powder in yields of 72–79%. Compound 2 can also be obtained by the hydrothermal reaction of MoO3, pzpy, and H2O at 160 °C for 3 d. Secondary products isolated from the reaction solutions included the salt (pzpyH)2(MoCl4) (3) (pzpyH = 2-[3(5)-pyrazolyl]pyridinium), containing a very rare example of the tetrahedral MoCl4(2–) anion, and the tetranuclear compound [Mo4O12(pzpy)4] (4). Reaction of 2 with excess tert-butylhydroperoxide (TBHP) led to the isolation of the oxodiperoxo complex [MoO(O2)2(pzpy)] (5). Single-crystal X-ray structures of 3 and 5 are described. Fourier transform (FT)-IR and FT Raman spectra for 1, 4, and 5 were assigned based on density functional theory calculations. The structure of 2 was determined from synchrotron powder X-ray diffraction data in combination with other physicochemical information. In 2, a hybrid organic–inorganic one-dimensional (1D) polymer, ∞(1)[Mo3O9(pzpy)], is formed by the connection of two very distinct components: a double ladder-type inorganic core reminiscent of the crystal structure of MoO3 and 1D chains of corner-sharing distorted {MoO4N2} octahedra. Compound 2 exhibits moderate activity and high selectivity when used as a (pre)catalyst for the epoxidation of cis-cyclooctene with TBHP. Under the reaction conditions used, 2 is poorly soluble and is gradually converted into 5, which is at least partly responsible for the catalytic reaction.

  14. Acrylate intercalation and in situ polymerization in iron-, cobalt-, or manganese-substituted nickel hydroxides.

    PubMed

    Vaysse, C; Guerlou-Demourgues, L; Duguet, E; Delmas, C

    2003-07-28

    A chimie douce route based on successive redox and exchange reactions has allowed us to prepare new hybrid organic-inorganic materials, composed of polyacrylate macromolecules intercalated into layered double hydroxides (LDHs), deriving from Ni(OH)(2). Monomer intercalation and in situ polymerization mechanisms have appeared to be strongly dependent upon the nature of the substituting cation in the slabs. In the case of iron-based LDHs, a phase containing acrylate monomeric intercalates has been isolated and identified by X-ray diffraction and infrared spectroscopy. Second, interslab free-radical polymerization of acrylate anions has been successfully initiated using potassium persulfate. In cobalt- or manganese-based LDHs, one-step polymerization has been observed, leading directly to a material containing polyacrylate intercalate.

  15. Effect of Surfactant Addition During Polymerization on Properties of PEDOT:PSS for Electronic Applications

    NASA Astrophysics Data System (ADS)

    Romyen, Nathavat; Thongyai, Supakanok; Praserthdam, Piyasan; Wacharawichanant, Sirirat

    2017-08-01

    Various kinds of surfactant (anionic, cationic, and zwitterionic) have been incorporated during the polymerization step to investigate their effect on the properties of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) molecules. Emulsification and polymerization of PEDOT together with surfactants were applied simultaneously to promote spherical shape of PEDOT:PSS particles and to enhance their conductivity and thermal properties. Transmission electron microscopy revealed that spherical particles with good dispersion were achieved on addition of 0.5 wt.% cationic surfactants. Moreover, the highest conductivity of 0.65 S/cm was also obtained at this condition. The interaction between the surfactants and the PEDOT or PSS molecules during the polymerization step played a key role in enhancing the thermal stability of the PEDOT:PSS in different ways. The possible mechanisms of interaction between each kind of surfactant and the PEDOT:PSS molecules are described.

  16. Observation by sup 13 C NMR of the EPSP synthase tetrahedral intermediate bound to the enzyme active site

    SciTech Connect

    Anderson, K.S.; Sammons, R.D.; Leo, G.C.; Sikorski, J.A. ); Benesi, A.J.; Johnson, K.A. )

    1990-02-13

    Direct observation of the tetrahedral intermediate in the EPSP synthase reaction pathway was provided by {sup 13}C NMR by examining the species bound to the enzyme active site under internal equilibrium conditions and using (2-{sup 13}C)PEP as a spectroscopic probe. The tetrahedral center of the intermediate bound to the enzyme gave a unique signal appearing at 104 ppm. Separate signals were observed for free EPSP and EPSP bound to the enzyme in a ternary complex with phosphate. These peak assignments account for the quantitation of the species bound to the enzyme and liberated upon quenching with either triethylamine or base. A comparison of quenching with acid, base, or triethylamine was conducted. After long times of incubation during the NMR measurement, a signal at 107 ppm appeared. The compound giving rise to this resonance was isolated and identified as an EPSP ketal. The rate of formation of the EPSP ketal was very slow establishing that it is a side product of the normal enzymatic reaction. To look for additional signals that might arise from a covalent adduct which has been postulated to arise from reaction of enzyme with PEP, and NMR experiment was performed with an analogue of S3P lacking the 4- and 5-hydroxyl groups. All of these results reaffirm identification of the tetrahedral species as the only observable intermediate in the EPSP synthase reaction.

  17. Synthesis and Catalytic Activity of Pt Monolayer on Pd Tetrahedral Nanocrystals with CO-adsorption-induced Removal of Surfactants

    SciTech Connect

    Gong K.; Vukmirovic M.B.; Ma C.; Zhu Y.; Adzic R.R.

    2011-11-01

    We synthesized the Pt monolayer shell-Pd tetrahedral core electrocatalysts that are notable for their high activity and stable performance. A small number of low-coordination sites and defects, and high content of the (1 1 1)-oriented facets on Pd tetrahedron makes them a suitable support for a Pt monolayer to obtain an active O{sub 2} reduction reaction (ORR) electrocatalyst. The surfactants, used to control size and shape of Pd tetrahedral nanoparticles, are difficult to remove and cause adverse effects on the ORR. We describe a simple and noninvasive method to synthesize high-purity tetrahedral Pd nanocrystals (TH Pd) by combining a hydrothermal route and CO adsorption-induced removal of surfactants. Poly(vinylpyrrolidone) (PVP), used as a protecting and reducing agent in hydrothermal reactions, is strongly bonded to the surface of the resulting nanocrystals. We demonstrate that PVP was displaced efficiently by adsorbed CO. A clean surface was achieved upon CO stripping at a high potential (1.0 V vs RHE). It played a decisive role in improving the activity of the Pt monolayer/TH Pd electrocatalyst for the ORR. Furthermore, the results demonstrate a versatile method for removal of surfactants from various nanoparticles that severely limited their applications.

  18. Tetrahedral shapes of neutron-rich Zr isotopes from a multidimensionally constrained relativistic Hartree-Bogoliubov model

    NASA Astrophysics Data System (ADS)

    Zhao, Jie; Lu, Bing-Nan; Zhao, En-Guang; Zhou, Shan-Gui

    2017-01-01

    We develop a multidimensionally constrained relativistic Hartree-Bogoliubov (MDC-RHB) model in which the pairing correlations are taken into account by making the Bogoliubov transformation. In this model, the nuclear shape is assumed to be invariant under the reversion of x and y axes; i.e., the intrinsic symmetry group is V4 and all shape degrees of freedom βλ μ with even μ are included self-consistently. The RHB equation is solved in an axially deformed harmonic oscillator basis. A separable pairing force of finite range is adopted in the MDC-RHB model. The potential energy curves of neutron-rich even-even Zr isotopes are calculated with relativistic functionals DD-PC1 and PC-PK1 and possible tetrahedral shapes in the ground and isomeric states are investigated. The ground state shape of 110Zr is predicted to be tetrahedral with both functionals and so is that of 112Zr with the functional DD-PC1. The tetrahedral ground states are caused by large energy gaps around Z =40 and N =70 when β32 deformation is included. Although the inclusion of the β30 deformation can also reduce the energy around β20=0 and lead to minima with pear-like shapes for nuclei around 110Zr, these minima are unstable due to their shallowness.

  19. Activity of Cu{sup 2+} ions on the tetrahedral and octahedral sites of spinel oxide catalysts for CO oxidation

    SciTech Connect

    Ghose, J.; Murthy, K.S.R.C.

    1996-09-01

    In studies of CO oxidation on substituted copper chromite spinel oxide catalyst decreases as the Cu{sup 2+} content of the catalyst decreases, either by substitution with a divalent ion, i.e., Cu{sub 1-x} Mg{sub x} [Cr{sub 2}]O{sub 4}, or by reduction of Cu{sup 2+} to Cu{sup 1+}. Crystallographic studies have shown that Cu[Cr{sub 2}]O{sub 4} changes from normal to partially inverse when Cr{sup 3+} is replaced by Al{sup 3+}. Thus, in aluminum-substituted copper chromite catalysts, copper is present on both tetrahedral and octahedral sites of the spinel lattice, i.e., Cu{sub 1-x}Al{sub x} [Cu{sub x}Cr{sub 2-(x+y)}Al{sub y}]O{sub 4}. ESCA studies have shown that upon Al substitution some of the tetrahedral Cu{sup 2+} ions are reduced to Cu{sup 1+} and this causes a reduction in the catalytic activity of the catalysts. The present work was taken up to compare the activity of Cu{sup 2+} on tetrahedral sites with that on octahedral sites of the spinel oxide catalysts. For this, CO oxidation studies were carried out on the inverse spinel CuFe{sub 2}O{sub 4} and on the normal spinel CuRh{sub 2}O{sub 4} catalysts. 7 refs., 1 fig.

  20. Computing Normal Shock-Isotropic Turbulence Interaction With Tetrahedral Meshes and the Space-Time CESE Method

    NASA Astrophysics Data System (ADS)

    Venkatachari, Balaji Shankar; Chang, Chau-Lyan

    2016-11-01

    The focus of this study is scale-resolving simulations of the canonical normal shock- isotropic turbulence interaction using unstructured tetrahedral meshes and the space-time conservation element solution element (CESE) method. Despite decades of development in unstructured mesh methods and its potential benefits of ease of mesh generation around complex geometries and mesh adaptation, direct numerical or large-eddy simulations of turbulent flows are predominantly carried out using structured hexahedral meshes. This is due to the lack of consistent multi-dimensional numerical formulations in conventional schemes for unstructured meshes that can resolve multiple physical scales and flow discontinuities simultaneously. The CESE method - due to its Riemann-solver-free shock capturing capabilities, non-dissipative baseline schemes, and flux conservation in time as well as space - has the potential to accurately simulate turbulent flows using tetrahedral meshes. As part of the study, various regimes of the shock-turbulence interaction (wrinkled and broken shock regimes) will be investigated along with a study on how adaptive refinement of tetrahedral meshes benefits this problem. The research funding for this paper has been provided by Revolutionary Computational Aerosciences (RCA) subproject under the NASA Transformative Aeronautics Concepts Program (TACP).