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Sample records for catalytic asymmetric addition

  1. Catalytic asymmetric addition of Grignard reagents to alkenyl-substituted aromatic N-heterocycles

    NARCIS (Netherlands)

    Jumde, Ravindra P; Lanza, Francesco; Veenstra, Marieke J; Harutyunyan, Syuzanna R

    2016-01-01

    Catalytic asymmetric conjugate addition reactions represent a powerful strategy to access chiral molecules in contemporary organic synthesis. However, their applicability to conjugated alkenyl-N-heteroaromatic compounds, of particular interest in medicinal chemistry, has lagged behind applications

  2. Catalytic asymmetric synthesis of acyclic arrays by tandem 1,4-addition-aldol reactions

    NARCIS (Netherlands)

    Howell, Gareth P.; Fletcher, Stephen P.; Geurts, Koen; ter Horst, Bjorn; Feringa, Ben L.

    2006-01-01

    Herein, we report efficient acyclic stereocontrol in tandem 1,4-addition-aldol reactions triggered by catalytic asymmetric organometallic addition. Grignard reagents add to alpha,beta-unsaturated thioesters in a 1,4-fashion and the resulting magnesium enolatesare trapped with aromatic or aliphatic

  3. Exploring the Catalytic Promiscuity of Phenolic Acid Decarboxylases: Asymmetric, 1,6-Conjugate Addition of Nucleophiles Across 4-Hydroxystyrene.

    Science.gov (United States)

    Payer, Stefan E; Sheng, Xiang; Pollak, Hannah; Wuensch, Christiane; Steinkellner, Georg; Himo, Fahmi; Glueck, Silvia M; Faber, Kurt

    2017-06-19

    The catalytic promiscuity of a ferulic acid decarboxylase from Enterobacter sp. (FDC_ E s) and phenolic acid decarboxylases (PADs) for the asymmetric conjugate addition of water across the C=C bond of hydroxystyrenes was extended to the N-, C- and S-nucleophiles methoxyamine, cyanide and propanethiol to furnish the corresponding addition products in up to 91% ee . The products obtained from the biotransformation employing the most suitable enzyme/nucleophile pairs were isolated and characterized after optimizing the reaction conditions. Finally, a mechanistic rationale supported by quantum mechanical calculations for the highly ( S )-selective addition of cyanide is proposed.

  4. Catalytic asymmetric alkylation of ketones using organometallic reagents

    NARCIS (Netherlands)

    Madduri, Ashoka V.R.; Harutyunyan, Syuzanna R.; Minnaard, Adriaan J.

    2013-01-01

    The catalytic asymmetric synthesis of tertiary alcohols by the addition of organometallic reagents to ketones is of central importance in organic chemistry. The resulting quaternary stereocentres are difficult to prepare selectively by other means despite their widespread occurrence in natural

  5. Catalytic enantioselective conjugate addition with Grignard reagents

    NARCIS (Netherlands)

    Lopez, Fernando; Minnaard, Adriaan J.; Feringa, Ben L.

    In this Account, recent advances in catalytic asymmetric conjugate addition of Grignard reagents are discussed. Synthetic methodology to perform highly enantioselective Cu-catalyzed conjugate addition of Grignard reagents to cyclic enones with ee's up to 96% was reported in 2004 from our

  6. Catalytic asymmetric alkylation of acylsilanes

    NARCIS (Netherlands)

    Rong, Jiawei; Oost, Rik; Desmarchelier, Alaric; Minnaard, Adriaan J; Harutyunyan, Syuzanna R

    2015-01-01

    The highly enantioselective addition of Grignard reagents to acylsilanes is catalyzed by copper diphosphine complexes. This transformation affords -silylated tertiary alcohols in up to 97% yield and 98:2 enantiomeric ratio. The competing Meerwein-Ponndorf-Verley reduction is suppressed by the use of

  7. Microscale Synthesis of Chiral Alcohols via Asymmetric Catalytic Transfer Hydrogenation

    Science.gov (United States)

    Peeters, Christine M.; Deliever, Rik; De Vos, Dirk

    2009-01-01

    Synthesis of pure enantiomers is a key issue in industry, especially in areas connected to life sciences. Catalytic asymmetric synthesis has emerged as a powerful and practical tool. Here we describe an experiment on racemic reduction and asymmetric reduction via a catalytic hydrogen transfer process. Acetophenone and substituted acetophenones are…

  8. Metal-Catalyzed Asymmetric Michael Addition in Natural Product Synthesis.

    Science.gov (United States)

    Hui, Chunngai; Pu, Fan; Xu, Jing

    2017-03-23

    Asymmetric catalysis for chiral compound synthesis is a rapidly growing field in modern organic chemistry. Asymmetric catalytic processes have been indispensable for the synthesis of enantioselective materials to meet demands from various fields. Michael addition has been used extensively for the construction of C-C bonds under mild conditions. With the discovery and development of organo- and metal-catalyzed asymmetric Michael additions, the synthesis of enantioselective and/or diastereoselective Michael adducts has become possible and increasingly prevalent in the literature. In particular, metal-catalyzed asymmetric Michael addition has been employed as a key reaction in natural product synthesis for the construction of contiguous quaternary stereogenic center(s), which is still a difficult task in organic synthesis. Previously reported applications of metal-catalyzed asymmetric Michael additions in natural product synthesis are presented here and discussed in depth. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Asymmetric Conjugate Addition of Grignard Reagents to Pyranones

    NARCIS (Netherlands)

    Mao, Bin; Fananas Mastral, Martin; Feringa, Ben L.

    2013-01-01

    An efficient enantioselective synthesis of lactones was developed based on the catalytic asymmetric conjugate addition (ACA) of alkyl Grignard reagents to pyranones. The use of 2H-pyran-2-one for the first time in the ACA with Grignard reagents allows for a variety of further transformations to

  10. Asymmetric conjugate addition of alkylzirconium reagents to α,β-unsaturated lactones.

    Science.gov (United States)

    Maciver, Eleanor E; Maksymowicz, Rebecca M; Wilkinson, Nancy; Roth, Philippe M C; Fletcher, Stephen P

    2014-06-20

    The asymmetric synthesis of β-substituted lactones by catalytic asymmetric conjugate addition of alkyl groups to α,β-unsaturated lactones is reported. The method uses alkylzirconium nucleophiles prepared in situ from alkenes and the Schwartz reagent. Enantioselective additions to 6- and 7-membered lactones proceed at rt, tolerate a wide variety of functional groups, and are readily scalable. The method was used in a formal asymmetric synthesis of mitsugashiwalactone.

  11. Catalytic Asymmetric Synthesis of Dihydrofurans and Cyclopentenols with Tertiary Stereocenters

    NARCIS (Netherlands)

    Wu, Zhongtao; Madduri, Ashoka V.R.; Harutyunyan, Syuzanna R.; Minnaard, Adriaan J.

    A new asymmetric synthesis of dihydrofurans and cyclopentenols has been developed and is based on the copper-catalyzed 1,2-addition of Grignard reagents to enones in combination with Sonogashira coupling/cyclization or ring-closing metathesis. By this approach, dihydrofurans with an

  12. Catalytic Asymmetric Roskamp Reaction of Silyl Diazoalkane: Synthesis of Enantioenriched α-Silyl Ketone.

    Science.gov (United States)

    Kim, Jae Yeon; Kang, Byung Chul; Ryu, Do Hyun

    2017-11-03

    A catalytic enantioselective Roskamp reaction of silyl diazoalkane to synthesize a highly optically active α-silyl ketone from aldehydes is described. In the presence of a chiral oxazaborolidinium ion catalyst, the reaction provides α-chiral silyl ketones with good yields (up to 97%) and high enantioselectivities (up to >99% ee). In addition, a one-pot procedure using an asymmetric Roskamp/reduction strategy gives highly optically active syn-β-hydroxysilane in good yields (up to 94%) with high enantioselectivities (up to 99% ee) and syn stereoselectivities (>20:1).

  13. Additive Manufacturing of Catalytically Active Living Materials.

    Science.gov (United States)

    Saha, Abhijit; Johnston, Trevor G; Shafranek, Ryan T; Goodman, Cassandra J; Zalatan, Jesse G; Storti, Duane W; Ganter, Mark A; Nelson, Alshakim

    2018-04-10

    Living materials, which are composites of living cells residing in a polymeric matrix, are designed to utilize the innate functionalities of the cells to address a broad range of applications such as fermentation and biosensing. Herein, we demonstrate the additive manufacturing of catalytically active living materials (AMCALM) for continuous fermentation. A multi-stimuli-responsive yeast-laden hydrogel ink, based on F127-dimethacrylate, was developed and printed using a direct-write 3D printer. The reversible stimuli-responsive behaviors of the polymer hydrogel inks to temperature and pressure are critical, as they enabled the facile incorporation of yeast cells and subsequent fabrication of 3D lattice constructs. Subsequent photo-cross-linking of the printed polymer hydrogel afforded a robust elastic material. These yeast-laden living materials were metabolically active in the fermentation of glucose into ethanol for 2 weeks in a continuous batch process without significant reduction in efficiency (∼90% yield of ethanol). This cell immobilization platform may potentially be applicable toward other genetically modified yeast strains to produce other high-value chemicals in a continuous biofermentation process.

  14. Catalytic Asymmetric Nitro-Mannich Reactions with a Yb/K Heterobimetallic Catalyst

    Directory of Open Access Journals (Sweden)

    Tatsuya Nitabaru

    2010-03-01

    Full Text Available A catalytic asymmetric nitro-Mannich (aza-Henry reaction with rare earth metal/alkali metal heterobimetallic catalysts is described. A Yb/K heterobimetallic catalyst assembled by an amide-based ligand promoted the asymmetric nitro-Mannich reaction to afford enantioenriched anti-b-nitroamines in up to 86% ee. Facile reduction of the nitro functionality allowed for efficient access to optically active 1,2-diamines.

  15. Recent advances in the catalytic asymmetric synthesis of β-amino acids

    NARCIS (Netherlands)

    Weiner, Barbara; Szymanski, Wiktor; Janssen, Dick B.; Minnaard, Adriaan J.; Feringa, Ben L.

    2010-01-01

    In this critical review, the progress in catalytic asymmetric synthesis of β-amino acids is discussed, covering the literature since 2002. The review treats transition metal catalysis, organocatalysis and biocatalysis and covers the most important synthetic methods, such as hydrogenation, the

  16. A Catalytic, Asymmetric Formal Synthesis of (+)-Hamigeran B

    KAUST Repository

    Mukherjee, Herschel

    2011-03-04

    A concise asymmetric, formal synthesis of (+)-hamigeran B is reported. A Pd-catalyzed, decarboxylative allylic alkylation, employing a trifluoromethylated derivative of t-BuPHOX, is utilized as the enantioselective step to form the critical quaternary carbon center in excellent yield and enantioselectivity. The product is converted in three steps to a late-stage intermediate previously used in the synthesis of hamigeran B.

  17. Direct Catalytic Asymmetric Mannich-Type Reaction of Alkylamides.

    Science.gov (United States)

    Arteaga, Fernando Arteaga; Liu, Zijian; Brewitz, Lennart; Chen, Jianyang; Sun, Bo; Kumagai, Naoya; Shibasaki, Masakatsu

    2016-05-20

    Direct enolate formation coupled with subsequent enantioselective C-C bond formation remains a topic of intense interest in asymmetric catalysis. This methodology is achieved even with low acidic amides without an electron-withdrawing group at the α-position in the context of a Mannich-type reaction. Acetate-, propionate-, and butyrate-type 7-azaindoline amides served as enolate precursors to afford the desired Mannich adducts with high stereoselectivity, and ligand-enabled diastereo-divergency provided access to both anti/syn diastereomers. The facile transformation of the amide moiety ensures the synthetic utility of the Mannich adducts.

  18. Green Synthesis of (R)-Terbutaline for Recyclable Catalytic Asymmetric Transfer Hydrogenation in Ionic Liquids.

    Science.gov (United States)

    Uchimoto, Hitomi; Ikeda, Miki; Tanida, Saori; Ohhashi, Kayo; Chihara, Yoshiko; Shigeta, Takashi; Arimitsu, Kenji; Yamashita, Masayuki; Nishide, Kiyoharu; Kawasaki, Ikuo

    2017-01-01

    We synthesize optically active (R)-terbutaline 2, which is an anti-asthmatic drug, through recyclable catalytic asymmetric transfer hydrogenation (RCATH). Various chloroketones 4 were prepared and RCATH was performed on them. The products exhibit moderate to high enantioselectivity. In particular, the hydrogenation of acyl substituted substrates 4c yields chiral secondary alcohols 5c in good yield and enantioselectivity. Furthermore, (R)-terbutaline 2 can be synthesized in one step from the resulting secondary alcohol 5 without racemization.

  19. α-Halo Amides as Competent Latent Enolates: Direct Catalytic Asymmetric Mannich-Type Reaction.

    Science.gov (United States)

    Sun, Bo; Balaji, Pandur Venkatesan; Kumagai, Naoya; Shibasaki, Masakatsu

    2017-06-21

    α-Halogenated carbonyl compounds are susceptible to dehalogenation and thus largely neglected as enolate precursors in catalytic enantioselective C-C bond-forming reactions. By merging the increased stability of the α-C-halogen bond of amides and the direct enolization methodology of the designed amide, we explored a direct catalytic asymmetric Mannich-type reaction of α-halo 7-azaindoline amides with N-carbamoyl imines. All α-halo substituents, α-F, -Cl, -Br, -I amides, were tolerated to provide the Mannich-adducts in a highly stereoselective manner without undesirable dehalogenation. The diastereoselectivity switched intriguingly depending on the substitution pattern of the aromatic imines, which is ascribed to stereochemical differentiation based on the open transition-state model. Functional group interconversion of the 7-azaindoline amide moiety of the Mannich-adducts and further elaboration into a diamide without dehalogenation highlight the synthetic utility of the present protocol for accessing enantioenriched halogenated chemical entities.

  20. Asymmetric Aldol Additions: A Guided-Inquiry Laboratory Activity on Catalysis

    Science.gov (United States)

    King, Jorge H. Torres; Wang, Hong; Yezierski, Ellen J.

    2018-01-01

    Despite the importance of asymmetric catalysis in both the pharmaceutical and commodity chemicals industries, asymmetric catalysis is under-represented in undergraduate chemistry laboratory curricula. A novel guided-inquiry experiment based on the asymmetric aldol addition was developed. Students conduct lab work to compare the effectiveness of…

  1. Asymmetric Conjugate Addition of α-Cyanoketones to Enones Using Diaminomethylenemalononitrile Organocatalyst.

    Science.gov (United States)

    Nakashima, Kosuke; Noda, Yuta; Hirashima, Shin-Ichi; Koseki, Yuji; Miura, Tsuyoshi

    2018-02-16

    A diaminomethylenemalononitrile organocatalyst efficiently catalyzed the asymmetric conjugate addition of α-cyanoketones to vinyl ketones to give the corresponding 1,5-dicarbonyl compounds, which bear an all-carbon quaternary stereogenic center with high enantioselectivities. This report is the first example of the asymmetric conjugate addition of α-cyanoketones to vinyl ketones using an organocatalyst.

  2. Ring-Contraction Strategy for the Practical, Scalable, Catalytic Asymmetric Synthesis of Versatile γ-Quaternary Acylcyclopentenes

    KAUST Repository

    Hong, Allen Y.

    2011-02-24

    Contraction action! A simple protocol for the catalytic asymmetric synthesis of highly functionalized γ-quaternary acylcyclopentenes (see schematic) in up to 91 % overall yield and 92 % ee has been developed. The reaction sequence employs a palladium-catalyzed enantioselective alkylation reaction and exploits the unusual stability of β-hydroxy cycloheptanones to achieve a general and robust method for performing two-carbon ring contractions.

  3. Synthesis of New Chiral Ligands Based on Thiophene Derivatives for Use in Catalytic Asymmetric Oxidation of Sulfides

    International Nuclear Information System (INIS)

    Jeong, Yong Chul; Ahn, Dae Jun; Lee, Woo Sun; Lee, Seung Han; Ahn, Kwang Hyun

    2011-01-01

    We discovered that the vanadium complexes of new Schiff base ligands and prepared from thiophene derivatives efficiently catalyze the asymmetric oxidation of sulfides by hydrogen peroxide to provide sulfoxides with enantioselectivities up to 79% ee and in yields up to 89%. Notably, Schiff base showed better or similar enantioselectivity than the well-studied Schiff base. These results suggest possible applications of Schiff bases derived from and in other catalytic asymmetric reactions. Chiral sulfoxides are important functional groups for various applications. For example, the biological activities of sulfoxide containing drugs such as omeprazole are strongly related to the chirality of the sulfoxide group; for this reason, esomeprazole, the enantiomerically pure form of omeprazole, was later developed. There are several chiral sulfoxide based drugs that have been introduced by the pharmaceutical industry including armodafinil, aprikalim, oxisurane, and ustiloxin. Chiral sulfoxides have also been utilized as chiral auxiliaries in asymmetric syntheses of chiral intermediates

  4. Catalytic enantioselective addition of Grignard reagents to aromatic silyl ketimines

    NARCIS (Netherlands)

    Rong, Jiawei; Collados, Juan F.; Ortiz, Pablo; Jumde, Ravindra P; Otten, Edwin; Harutyunyan, Syuzanna R

    2016-01-01

    α-Chiral amines are of significant importance in medicinal chemistry, asymmetric synthesis and material science, but methods for their efficient synthesis are scarce. In particular, the synthesis of α-chiral amines with the challenging tetrasubstituted carbon stereocentre is a long-standing problem

  5. Iterative Cr-mediated catalytic asymmetric allylation to synthesize syn/syn- and anti/anti-1,3,5-triols.

    Science.gov (United States)

    Zhang, Zhiyu; Aubry, Sylvain; Kishi, Yoshito

    2008-07-17

    Iterative use of Cr-mediated catalytic asymmetric allylation could give a simple access to 1,3-polyols. Using syn/syn- and anti/anti-1,3,5-triols as representative examples, the feasibility of this approach is studied, thereby demonstrating that (1) the pre-existing TMS-protected alcohol at the beta-position does not give a significant effect on the Cr-mediated catalytic asymmetric allylation and (2) this synthetic route furnishes the expected syn/syn- and anti/anti-1,3,5-triols at the useful level of asymmetric induction and yield.

  6. Copper-catalyzed asymmetric conjugate addition of Grignard reagents to cyclic enones

    NARCIS (Netherlands)

    Feringa, Bernard; Badorrey, R; Pena, D; Harutyunyan, [No Value; Minnaard, AJ; Harutyunyan, Syuzanna R.

    2004-01-01

    It is no longer necessary to use dialkylzinc reagents to obtain enantioselectivities >95% in the copper-catalyzed asymmetric conjugate addition of organometallic compounds to cyclic enones. We now report how this can be accomplished by using inexpensive and readily available Grignard reagents.

  7. Catalytic Asymmetric Mannich Reaction with N-Carbamoyl Imine Surrogates of Formaldehyde and Glyoxylate.

    Science.gov (United States)

    You, Yang'en; Zhang, Long; Cui, Linfeng; Mi, Xueling; Luo, Sanzhong

    2017-10-23

    N,O-acetals (NOAcs) were developed as bench stable surrogates for N-carbamoyl, (Boc, Cbz and Fmoc) formaldehyde and glyoxylate imines in asymmetric Mannich reactions. The NOAcs can be directly utilized in the chiral primary amine catalyzed Mannich reactions of both acyclic and cyclic β-ketocarbonyls with high yields and excellent stereoselectivity. The current reaction offers a straightforward approach in the asymmetric synthesis of α- or β-amino carbonyls bearing chiral quaternary centers in a practical and highly stereocontrolled manner. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Continuous-flow catalytic asymmetric hydrogenations: Reaction optimization using FTIR inline analysis

    Directory of Open Access Journals (Sweden)

    Magnus Rueping

    2012-02-01

    Full Text Available The asymmetric organocatalytic hydrogenation of benzoxazines, quinolines, quinoxalines and 3H-indoles in continuous-flow microreactors has been developed. Reaction monitoring was achieved by using an inline ReactIR flow cell, which allows fast and convenient optimization of reaction parameters. The reductions proceeded well, and the desired products were isolated in high yields and with excellent enantioselectivities.

  9. Catalytic asymmetric allylation of aliphatic aldehydes by chiral bipyridine N,N'-dioxides

    Czech Academy of Sciences Publication Activity Database

    Hrdina, R.; Boyd, T.; Valterová, Irena; Hodačová, Jana; Kotora, Martin

    -, č. 20 (2008), s. 3141-3144 ISSN 0936-5214 Grant - others:GA MŠk(CZ) LC06070 Program:LC Institutional research plan: CEZ:AV0Z40550506 Keywords : allylations * aldehydes * Lewis base * asymmetric catalysis * solvent effect Subject RIV: CC - Organic Chemistry Impact factor: 2.659, year: 2008

  10. Catalytic asymmetric formation of delta-lactones from unsaturated acyl halides.

    Science.gov (United States)

    Tiseni, Paolo S; Peters, René

    2010-02-22

    Previously unexplored enantiopure zwitterionic ammonium dienolates have been utilized in this work as reactive intermediates that act as diene components in hetero-Diels-Alder reactions (HDAs) with aldehydes to produce optically active delta-lactones, subunits of numerous bioactive products. The dienolates were generated in situ from E/Z mixtures of alpha,beta-unsaturated acid chlorides by use of a nucleophilic quinidine derivative and Sn(OTf)(2) as co-catalyst. The latter component was not directly involved in the cycloaddition step with aldehydes and simply facilitated the formation of the reactive dienolate species. The scope of the cycloaddition was considerably improved by use of a complex formed from Er(OTf)(3) and a simple commercially available norephedrine-derived ligand that tolerated a broad range of aromatic and heteroaromatic aldehydes for a cooperative bifunctional Lewis-acid-/Lewis-base-catalyzed reaction, providing alpha,beta-unsaturated delta-lactones with excellent enantioselectivities. Mechanistic studies confirmed the formation of the dienolate intermediates for both catalytic systems. The active Er(III) complex is most likely a monomeric species. Interestingly, all lanthanides can catalyze the title reaction, but the efficiency in terms of yield and enantioselectivity depends directly on the radius of the Ln(III) ion. Similarly, use of the pseudolanthanides Sc(III) and Y(III) also resulted in product formation, whereas the larger La(III) and other transition metal salts, as well as main group metal salts, proved to be inefficient. In addition, various synthetic transformations of 6-CCl(3)- or 4-silyl-substituted alpha,beta-unsaturated delta-lactones, giving access to a number of valuable delta-lactone building blocks, were investigated.

  11. Direct Catalytic Asymmetric Mannich-Type Reaction of α-N3 Amide.

    Science.gov (United States)

    Sun, Zhongdong; Weidner, Karin; Kumagai, Naoya; Shibasaki, Masakatsu

    2015-12-01

    An α-N3 7-azaindoline amide serves as a latent enolate to directly engage in an asymmetric Mannich-type reaction with N-thiophosphinoyl imines by the action of a cooperative catalyst. The thus-obtained highly enantioenriched anti-adduct was transformed into β-amino-α-azido acid in high yield by simple acidic treatment. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Direct Catalytic Asymmetric Mannich-Type Reaction en Route to α-Hydroxy-β-amino Acid Derivatives.

    Science.gov (United States)

    Sun, Bo; Pluta, Roman; Kumagai, Naoya; Shibasaki, Masakatsu

    2018-02-02

    A direct catalytic Mannich-type reaction of α-oxygen-functionalized amides was achieved. The use of 7-azaindoline amide was crucial to facilitate direct enolization and subsequent stereoselective addition to imines in a cooperative catalytic system comprising a soft Lewis acid and Brønsted base. The operationally simple room-temperature protocol furnished a syn-Mannich adduct with high stereoselectivity. Divergent functional group transformation of the amide moiety of the product allowed for expeditious access to enantioenriched syn-configured α-hydroxy-β-amino carboxylic acid derivatives, highlighting the synthetic utility of the present catalysis.

  13. Asymmetric Anion-π Catalysis: Enamine Addition to Nitroolefins on π-Acidic Surfaces.

    Science.gov (United States)

    Zhao, Yingjie; Cotelle, Yoann; Avestro, Alyssa-Jennifer; Sakai, Naomi; Matile, Stefan

    2015-09-16

    Here we provide experimental evidence for anion-π catalysis of enamine chemistry and for asymmetric anion-π catalysis. A proline for enamine formation on one side and a glutamic acid for nitronate protonation on the other side are placed to make the enamine addition to nitroolefins occur on the aromatic surface of π-acidic naphthalenediimides. With increasing π acidity of the formally trifunctional catalysts, rate and enantioselectivity of the reaction increase. Mismatched and more flexible controls reveal that the importance of rigidified, precisely sculpted architectures increases with increasing π acidity as well. The absolute configuration of stereogenic sulfoxide acceptors at the edge of the π-acidic surface has a profound influence on asymmetric anion-π catalysis and, if perfectly matched, affords the highest enantio- and diastereoselectivity.

  14. Engineering the donor selectivity of D-fructose-6-phosphate aldolase for biocatalytic asymmetric cross-aldol additions of glycolaldehyde.

    Science.gov (United States)

    Szekrenyi, Anna; Soler, Anna; Garrabou, Xavier; Guérard-Hélaine, Christine; Parella, Teodor; Joglar, Jesús; Lemaire, Marielle; Bujons, Jordi; Clapés, Pere

    2014-09-22

    D-Fructose-6-phosphate aldolase (FSA) is a unique catalyst for asymmetric cross-aldol additions of glycolaldehyde. A combination of a structure-guided approach of saturation mutagenesis, site-directed mutagenesis, and computational modeling was applied to construct a set of FSA variants that improved the catalytic efficiency towards glycolaldehyde dimerization up to 1800-fold. A combination of mutations in positions L107, A129, and A165 provided a toolbox of FSA variants that expand the synthetic possibilities towards the preparation of aldose-like carbohydrate compounds. The new FSA variants were applied as highly efficient catalysts for cross-aldol additions of glycolaldehyde to N-carbobenzyloxyaminoaldehydes to furnish between 80-98 % aldol adduct under optimized reaction conditions. Donor competition experiments showed high selectivity for glycolaldehyde relative to dihydroxyacetone or hydroxyacetone. These results demonstrate the exceptional malleability of the active site in FSA, which can be remodeled to accept a wide spectrum of donor and acceptor substrates with high efficiency and selectivity. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Copper-catalyzed asymmetric conjugate addition of organometallic reagents to extended Michael acceptors

    Directory of Open Access Journals (Sweden)

    Thibault E. Schmid

    2015-12-01

    Full Text Available The copper-catalyzed asymmetric conjugate addition (ACA of nucleophiles onto polyenic Michael acceptors represents an attractive and powerful methodology for the synthesis of relevant chiral molecules, as it enables in a straightforward manner the sequential generation of two or more stereogenic centers. In the last decade, various chiral copper-based catalysts were evaluated in combination with different nucleophiles and Michael acceptors, and have unambiguously demonstrated their usefulness in the control of the regio- and enantioselectivity of the addition. The aim of this review is to report recent breakthroughs achieved in this challenging field.

  16. A study of catalytic behaviour of aromatic additives on the photo ...

    Indian Academy of Sciences (India)

    A study of catalytic behaviour of aromatic additives on the photo-Fenton degradation of phenol red. Abhilasha Jain ... The effect of variation of various parameters such as pH, concentration of dye, Fe3+ ion and additives, amount of H2O2, and light intensity on the rate of photodegradation was also observed. A tentative ...

  17. Asymmetric total synthesis of Apocynaceae hydrocarbazole alkaloids (+)-deethylibophyllidine and (+)-limaspermidine.

    Science.gov (United States)

    Du, Ji-Yuan; Zeng, Chao; Han, Xiao-Jie; Qu, Hu; Zhao, Xian-He; An, Xian-Tao; Fan, Chun-An

    2015-04-01

    An unprecedented asymmetric catalytic tandem aminolysis/aza-Michael addition reaction of spirocyclic para-dienoneimides has been designed and developed through organocatalytic enantioselective desymmetrization. A unified strategy based on this key tandem methodology has been divergently explored for the asymmetric total synthesis of two natural Apocynaceae alkaloids, (+)-deethylibophyllidine and (+)-limaspermidine. The present studies not only enrich the tandem reaction design concerning the asymmetric catalytic assembly of a chiral all-carbon quaternary stereocenter contained in the densely functionalized hydrocarbazole synthons but also manifest the potential for the application of the asymmetric catalysis based on the para-dienone chemistry in asymmetric synthesis of natural products.

  18. Metal-Free Catalytic Asymmetric Fluorination of Keto Esters Using a Combination of Hydrogen Fluoride (HF) and Oxidant: Experiment and Computation

    KAUST Repository

    Pluta, Roman

    2018-02-09

    A chiral iodoarene organocatalyst for the catalytic asymmetric fluorination has been developed. The catalyst was used in the asymmetric fluorination of carbonyl compounds, providing the products with a quaternary stereocenter with high enantioselectivities. Chiral hypervalent iodine difluoride intermediates were generated in situ by treatment of the catalyst with an oxidant and hydrogen fluoride as fluoride source. As such, the α-fluorination of a carbonyl compound was achieved with a nucleophilic fluorine source. A combined computational and experimental approach provided insight into the reaction mechanism and the origin of enantioselectivity.

  19. Correction: Synthesis of pyrrolidine-3-carboxylic acid derivatives via asymmetric Michael addition reactions of carboxylate-substituted enones.

    Science.gov (United States)

    Yin, Feng; Garifullina, Ainash; Tanaka, Fujie

    2018-04-25

    Correction for 'Synthesis of pyrrolidine-3-carboxylic acid derivatives via asymmetric Michael addition reactions of carboxylate-substituted enones' by Feng Yin et al., Org. Biomol. Chem., 2017, 15, 6089-6092.

  20. Catalytic Asymmetric Synthesis of Fluoroalkyl-Containing Compounds by Three-Component Photoredox Chemistry.

    Science.gov (United States)

    Ma, Jiajia; Xie, Xiulan; Meggers, Eric

    2018-01-02

    Multicomponent reactions allow the construction of molecular complexity in an economical fashion, fluorinated compounds play an important role in pharmaceuticals and agrochemicals, whereas visible light is an abundant and sustainable source of energy for activating chemical transformations. Here we report a visible-light-induced asymmetric three-component fluoroalkylation reaction scheme catalyzed by a chiral-at-rhodium Lewis acid. The photoredox process is mediated by the inexpensive, commercially available organic photoredox mediator 4,4'-difluorobenzil, which upon activation by visible light induces the generation of perfluoroalkyl radicals from their sulfinates via single electron transfer oxidation. The fluorinated radicals are trapped by electron-rich C-C double bonds to deliver α-oxy carbon-centered radicals, followed by a subsequent stereocontrolled reaction with acceptor-substituted alkenes. This three-component fluoroalkylation scheme provides a range of complex fluoroalkyl-containing chiral compounds under dual C-C bond formation with high enantioselectivities (up to 98 % ee) and modest diastereoselectivities (up to 6:1 dr). Excellent diastereoselectivities (up to >38:1:1 dr) for natural chiral compound derivatives are observed. Broad substrate scope (25 examples), excellent functional group tolerance, scalability of the reaction, along with the option to recover the chiral catalyst and photoredox mediator reveal the practicability of this methodology in organic synthesis for the rapid synthesis of fluorinated chiral molecules. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Photo initiated thermal cyclo dehydration of polyamide acid with catalytic addition

    International Nuclear Information System (INIS)

    Toirov, A.; Shukronaev, S.P.; Yusupov, I.Kh.

    1992-01-01

    This article is devoted to photo initiated thermal cyclo dehydration of polyamide acid with catalytic addition. Thereby, authors investigated some properties of photo initiated cyclo dehydration process of polyamide acid obtained from dianhydride of pyromellitic acid and 4.4-diaminodiphenyl ether with three-phenyl phosphate.

  2. Direct Catalytic Asymmetric Mannich-Type Reaction of α- and β-Fluorinated Amides.

    Science.gov (United States)

    Brewitz, Lennart; Arteaga, Fernando Arteaga; Yin, Liang; Alagiri, Kaliyamoorthy; Kumagai, Naoya; Shibasaki, Masakatsu

    2015-12-23

    The last two decades have witnessed the emergence of direct enolization protocols providing atom-economical and operationally simple methods to use enolates for stereoselective C-C bond-forming reactions, eliminating the inherent drawback of the preformation of enolates using stoichiometric amounts of reagents. In its infancy, direct enolization relied heavily on the intrinsic acidity of the latent enolates, and the reaction scope was limited to readily enolizable ketones and aldehydes. Recent advances in this field enabled the exploitation of carboxylic acid derivatives for direct enolization, offering expeditious access to synthetically versatile chiral building blocks. Despite the growing demand for enantioenriched fluorine-containing small molecules, α- and β-fluorinated carbonyl compounds have been neglected in direct enolization chemistry because of the competing and dominating defluorination pathway. Herein we present a comprehensive study on direct and highly stereoselective Mannich-type reactions of α- and β-fluorine-functionalized 7-azaindoline amides that rely on a soft Lewis acid/hard Brønsted base cooperative catalytic system to guarantee an efficient enolization while suppressing undesired defluorination. This protocol contributes to provide a series of fluorinated analogs of enantioenriched β-amino acids for medicinal chemistry.

  3. Catalytic steam reforming of acetic acid in a fluidized bed reactor with oxygen addition

    Energy Technology Data Exchange (ETDEWEB)

    Medrano, J.A.; Oliva, M.; Ruiz, J.; Garcia, L.; Arauzo, J. [Thermochemical Processes Group (GPT), Aragon Institute for Engineering Research (I3A), University of Zaragoza, Maria de Luna 3, 50018 Zaragoza (Spain)

    2008-08-15

    Catalytic steam reforming of bio-oil is a promising process for producing hydrogen in a sustainable environmentally friendly way that can improve the utilization of local resources (natural sources or wastes). However, there remain drawbacks such as coke formation that produce operational problems and deactivation of the catalysts. Coprecipitated Ni/Al catalysts are here used in a fluidized bed for reforming at 650 C of acetic acid as a model compound of bio-oil-aqueous fraction. Different strategies are applied in order to study their effects on the catalytic steam reforming process: modification of the catalyst by increasing the calcination temperature or adding promoters such as calcium. The addition of small quantities of oxygen is also tested resulting in an optimum percentage to achieve a high carbon conversion process with less coke and without a hydrogen yield penalty production. The results for catalytic steam reforming are compared with other ones from literature. (author)

  4. Catalytic Asymmetric Piancatelli Rearrangement: Brønsted Acid Catalyzed 4π Electrocyclization for the Synthesis of Multisubstituted Cyclopentenones

    KAUST Repository

    Cai, Yunfei

    2016-10-13

    The first catalytic asymmetric Piancatelli reaction is reported. Catalyzed by a chiral Brønsted acid, the rearrangement of a wide range of furylcarbinols with a series of aniline derivatives provides valuable aminocyclopentenones in high yields as well as excellent enantioselectivities and diastereoselectivities. The high value of the aza-Piancatelli rearrangement was demonstrated by the synthesis of a cyclopentane-based hNK1 antagonist analogue.

  5. Catalytic asymmetric access to alpha,beta unsaturated delta-lactones through a vinylogous aldol reaction: application to the total synthesis of the Prelog-Djerassi lactone.

    Science.gov (United States)

    Bluet, G; Bazán-Tejeda, B; Campagne, J M

    2001-11-15

    [reaction--see text] A one-step catalytic asymmetric access to alpha,beta unsaturated delta-lactones is described, using a vinylogous Mukaiyama-aldol reaction between a gamma-substituted dienolate and various aldehydes in the presence of Carreira catalyst CuF.(S)-tolBinap. This methodology has been further applied to a straightforward access to the Prelog-Djerassi lactone.

  6. Catalytic enantioselective vinylogous Mukaiyama-Michael addition of 2-silyloxyfurans to cyclic unsaturated oxo esters.

    Science.gov (United States)

    Jusseau, Xavier; Retailleau, Pascal; Chabaud, Laurent; Guillou, Catherine

    2013-03-15

    The copper-catalyzed asymmetric addition of 2-silyloxyfurans to cyclic unsaturated oxo esters is reported. The reaction proceeds with excellent diastereocontrol (usually dr 99:1) and modest to high enantioselectivity, depending on the nature of the ester group and the substitution of the cyclic oxo ester. We have shown that these substrates can be transformed into a variety of building blocks bearing a γ-butenolide or γ-lactone connected to a cycloalkane or cycoalkene moiety.

  7. Asymmetric synthesis of cyclo-archaeol and beta-glucosyl cyclo-archaeol

    NARCIS (Netherlands)

    Ferrer, Catalina; Fodran, Peter; Barroso, Santiago; Gibson, Robert; Hopmans, Ellen C.; Damste, Jaap Sinninghe; Schouten, Stefan; Minnaard, Adriaan J.

    2013-01-01

    An efficient asymmetric synthesis of cyclo-archaeol and beta-glucosyl cyclo-archaeol is presented employing catalytic asymmetric conjugate addition and catalytic epoxide ring opening as the key steps. Their occurrence in deep sea hydrothermal vents has been confirmed by chromatographic comparison

  8. Catalytic enantioselective Michael addition reactions of alpha-nitroesters to alpha,beta-unsaturated ketones

    NARCIS (Netherlands)

    Keller, E; Veldman, N; Spek, AL; Feringa, BL

    1997-01-01

    Enantioselective Michael additions of alpha-nitroesters 2a-d with alpha,beta-unsaturated ketones were carried out in the presence of a catalytic amount of chiral Al-Li-(R,R')-2,2'-dihydroxy-1,1'-binaphthyl ('AlLiBINOL') complex prepared in situ from LiAlH4 and 2.45 equiv. of (R,R')-BINOL. The

  9. Catalytic enantioselective Michael addition reactions of α-nitroesters to α,β-unsaturated ketones

    NARCIS (Netherlands)

    Keller, Erik; Veldman, Nora; Spek, Anthony L.; Feringa, Bernard

    1997-01-01

    Enantioselective Michael additions of α-nitroesters 2a-d with α,β-unsaturated ketones were carried out in the presence of a catalytic amount of chiral Al-Li-(R,R')-2,2'-dihydroxy-1,1'-binaphthyl (‘AlLiBINOL’) complex prepared in situ from LiAlH4 and 2.45 equiv. of (R,R')-BINOL. The

  10. Catalytic

    Directory of Open Access Journals (Sweden)

    S.A. Hanafi

    2014-03-01

    Full Text Available A series of dealuminated Y-zeolites impregnated by 0.5 wt% Pt catalysts promoted by different amounts of Ni, Pd or Cr (0.3 and 0.6 wt% were prepared and characterized as hydrocracking catalysts. The physicochemical and structural characterization of the solid catalysts were investigated and reported through N2 physisorption, XRD, TGA-DSC, FT-IR and TEM techniques. Solid catalysts surface acidities were investigated through FT-IR spectroscopy aided by pyridine adsorption. The solid catalytic activities were evaluated through hydroconversion of n-hexane and n-heptane employing micro-catalytic pulse technique directly connected to a gas chromatograph analyzer. The thermal stability of the solids was also investigated up to 800 °C. Crystallinity studies using the XRD technique of all modified samples proved analogous to the parent Y-zeolite, exhibiting nearly an amorphous and microcrystalline character of the second metal oxides. Disclosure of bimetallic catalysts crystalline characterization, through XRD, was not viable. The nitrogen adsorption–desorption isotherms for all samples concluded type I adsorption isotherms, without any hysteresis loop, indicating that the entire pore system is composed of micropores. TEM micrographs of the solid catalysts demonstrate well-dispersed Pt, Ni and Cr nanoparticles having sizes of 2–4 nm and 7–8 nm, respectively. The catalytic activity results indicate that the bimetallic (0.5Pt–0.3Cr/D18H–Y catalyst is the most active towards n-hexane and n-heptane isomerization while (0.5Pt–0.6Ni/D18H–Y catalyst can be designed as most suitable as a cracking catalyst.

  11. Total Synthesis of (R, R, R)-gamma-Tocopherol through Cu-Catalyzed Asymmetric 1,2-Addition

    NARCIS (Netherlands)

    Wu, Zhongtao; Harutyunyan, Syuzanna R.; Minnaard, Adriaan J.

    2014-01-01

    Based on the asymmetric copper-catalyzed 1,2-addition of Grignard reagents to ketones, (R,R,R)--tocopherol has been synthesized in 36% yield over 12 steps (longest linear sequence). The chiral center in the chroman ring was constructed with 73% ee by the 1,2-addition of a phytol-derived Grignard

  12. The influence of catalytic additives on kinetics of coal gasification process

    Directory of Open Access Journals (Sweden)

    Zubek Katarzyna

    2017-01-01

    Full Text Available Catalytic coal gasification is a process that has the potential to become one of the efficient industrial technology of energy production. For this reason, the subject of this study was to analyze the kinetics of catalytic gasification of ‘Janina’ coal with steam. Isothermal measurements were performed at 800 °C, 900 °C, 950 °C and 1000 °C at a pressure of 1 MPa using cations of sodium, potassium and calcium as catalysts. During examination the thermovolumetric method was used. This method allows to determine the formation rates of a gaseous product such as carbon monoxide, hydrogen, methane and carbon dioxide as well as their contribution to the resulting gas. Moreover, the influence of catalysts on the kinetics of CO and H2 formation at various temperatures was determined and the kinetics parameters were calculated with the use of isoconversional model, Random Pore Model and Grain Model. The obtained results confirmed the positive effect of catalysts on the coal gasification process. The catalytic measurements were characterized by higher reaction rate and shorter duration of the process, and the calculated values of the kinetic parameters were lower than for the gasification process without the addition of catalysts.

  13. Asymmetric additions of thioglycolates and N-Boc aldimines catalyzed by a bifunctional tertiary-amine squaramide.

    Science.gov (United States)

    Feng, Bo-Xu; Wang, Bin; Li, Xin

    2016-10-21

    A highly enantioselective asymmetric addition reaction of thioglycolates and N-Boc aldimines was promoted by a bifunctional tertiary-amine squaramide catalyst. As a result, a number of chiral N,S-acetal derivatives were efficiently synthesized with good enantioselectivities.

  14. Synthesis and Catalytic Activity of Two New Cyclic Tetraaza Ligands

    Directory of Open Access Journals (Sweden)

    Burkhard König

    2003-05-01

    Full Text Available Two new chiral cyclic tetraaza ligands were synthesized and characterized. Their catalytic activity was tested in the asymmetric addition of diethylzinc to benzaldehyde. The expected secondary alcohol was obtained in moderate yields, but with very low enantioselectivity.

  15. Increasing Octane Value in Catalytic Cracking of n-Hexadecane with Addition of *BEA Type Zeolite

    Directory of Open Access Journals (Sweden)

    Iori Shimada

    2015-04-01

    Full Text Available In this study, multifunctional catalysts were developed by adding *BEA or MFI zeolite with high Si/Al ratio to a residual fluidized catalytic cracking (RFCC catalyst and tested in the catalytic cracking of n-hexadecane, which is a heavy crude oil model compound, for the purpose of increasing the octane value of produced gasoline under the strong hydrogen transfer activity of the RFCC catalyst. Reaction products analysis revealed that the addition of *BEA zeolite to the RFCC catalyst increased the yields of olefins and multi-branched paraffins, which resulted in improvement of the octane value without sacrificing gasoline yield. On the contrary, the addition of MFI zeolite decreased the gasoline yield because it cracks the gasoline range olefins into LPG range olefins. In general, it is difficult to increase the yield of multi-branched molecules because the multi-branched molecule is more easily cracked than linear molecules. Our results suggest the possibility for the selective acceleration of isomerization reaction by the addition of less acidic *BEA zeolite to the RFCC catalyst.

  16. Solvent dependent asymmetric hydrogenation with self-assembled catalysts: a combined catalytic, NMR- and IR-study.

    Science.gov (United States)

    Shuklov, Ivan A; Dubrovina, Natalia V; Barsch, Enrico; Ludwig, Ralf; Michalik, Dirk; Börner, Armin

    2009-03-28

    For the first time the hydrogen bond based structure of self-aggregated Rh-phosphine complexes in fluorinated alcohols was directly determined, which gives a rationale for the high enantioselectivity observed in the asymmetric hydrogenation.

  17. Catalytic diastereo- and enantioselective additions of versatile allyl groups to N-H ketimines

    Science.gov (United States)

    Jang, Hwanjong; Romiti, Filippo; Torker, Sebastian; Hoveyda, Amir H.

    2017-12-01

    There are many biologically active organic molecules that contain one or more nitrogen-containing moieties, and broadly applicable and efficient catalytic transformations that deliver them diastereoselectively and/or enantioselectively are much sought after. Various methods for enantioselective synthesis of α-secondary amines are available (for example, from additions to protected/activated aldimines), but those involving ketimines are much less common. There are no reported additions of carbon-based nucleophiles to unprotected/unactivated (or N-H) ketimines. Here, we report a catalytic, diastereo- and enantioselective three-component strategy for merging an N-H ketimine, a monosubstituted allene and B2(pin)2, affording products in up to 95% yield, >98% diastereoselectivity and >99:1 enantiomeric ratio. The utility of the approach is highlighted by synthesis of the tricyclic core of a class of compounds that have been shown to possess anti-Alzheimer activity. Stereochemical models developed with the aid of density functional theory calculations, which account for the observed trends and levels of enantioselectivity, are presented.

  18. Catalytic enantioselective addition of organoboron reagents to fluoroketones controlled by electrostatic interactions

    Science.gov (United States)

    Lee, Kyunga; Silverio, Daniel L.; Torker, Sebastian; Robbins, Daniel W.; Haeffner, Fredrik; van der Mei, Farid W.; Hoveyda, Amir H.

    2016-08-01

    Organofluorine compounds are central to modern chemistry, and broadly applicable transformations that generate them efficiently and enantioselectively are in much demand. Here we introduce efficient catalytic methods for the addition of allyl and allenyl organoboron reagents to fluorine-substituted ketones. These reactions are facilitated by readily and inexpensively available catalysts and deliver versatile and otherwise difficult-to-access tertiary homoallylic alcohols in up to 98% yield and >99:1 enantiomeric ratio. Utility is highlighted by a concise enantioselective approach to the synthesis of the antiparasitic drug fluralaner (Bravecto, presently sold as the racemate). Different forms of ammonium-organofluorine interactions play a key role in the control of enantioselectivity. The greater understanding of various non-bonding interactions afforded by these studies should facilitate the future development of transformations that involve fluoroorganic entities.

  19. Enhancing electrochemical methods for producing and regenerating alane by using electrochemical catalytic additive

    Science.gov (United States)

    Zidan, Ragaiy

    2017-12-26

    A process of using an electrochemical cell to generate aluminum hydride (AlH.sub.3) and other high capacity hydrides is provided. The electrolytic cell uses an electro-catalytic-additive within a polar non-salt containing solvent to solubilize an ionic hydride such as NaAlH.sub.4 or LiAlH.sub.4. The resulting electrochemical process results in the formation of AlH.sub.3 adduct. AlH.sub.3 is obtained from the adduct by heating under vacuum. The AlH.sub.3 can be recovered and used as a source of hydrogen for the automotive industry. The resulting spent aluminum can be regenerated into NaAlH.sub.4 or LiAlH.sub.4 as part of a closed loop process of AlH.sub.3 generation.

  20. Catalytic role of nickel in the decarbonylative addition of phthalimides to alkynes

    KAUST Repository

    Poater, Albert

    2013-11-11

    Density functional theory calculations have been used to investigate the catalytic role of nickel(0) in the decarbonylative addition of phthalimides to alkynes. According to Kurahashi et al. the plausible reaction mechanism involves a nucleophilic attack of nickel at an imide group, giving a six-membered metallacycle, followed by a decarbonylation and insertion of an alkyne leading to a seven-membered metallacycle. Finally a reductive elimination process produces the desired product and regenerates the nickel(0) catalyst. In this paper, we present a full description of the complete reaction pathway along with possible alternative pathways, which are predicted to display higher upper barriers. Our computational results substantially confirm the proposed mechanism, offering a detailed geometrical and energetical understanding of all the elementary steps. © 2013 American Chemical Society.

  1. Catalytic asymmetric Meerwein-Ponndorf-Verley reduction of glyoxylates induced by a chiral N,N'-dioxide/Y(OTf)3complex.

    Science.gov (United States)

    Wu, Wangbin; Zou, Sijia; Lin, Lili; Ji, Jie; Zhang, Yuheng; Ma, Baiwei; Liu, Xiaohua; Feng, Xiaoming

    2017-03-18

    An asymmetric Meerwein-Ponndorf-Verley (MPV) reduction of glyoxylates was for the first time accomplished via an N,N'-dioxide/Y(OTf) 3 complex with aluminium alkoxide and molecular sieves (MSs) as crucial additives. A variety of optically active α-hydroxyesters were obtained with excellent results. A possible reaction mechanism was proposed based on the experiments.

  2. Synthesis of (R)-BINOL-Derived (Cyclopentadienone)iron Complexes and Their Application in the Catalytic Asymmetric Hydrogenation of Ketones

    NARCIS (Netherlands)

    Gajewski, Piotr; Renom-Carrasco, Marc; Facchini, Sofia Vailati; Pignataro, Luca; Lefort, Laurent; de Vries, Johannes G.; Ferraccioli, Raffaella; Piarulli, Umberto; Gennari, Cesare

    A family of chiral (cyclopentadienone)iron complexes, featuring an (R)-BINOL-derived backbone, and their application in the asymmetric hydrogenation of ketones are described. The complexes differ from each other in the substituents at the 3,3-positions of the binaphthyl residue (H, OH, OR, OCOR,

  3. A Ligand Structure-Activity Study of DNA-Based Catalytic Asymmetric Hydration and Diels-Alder Reactions

    NARCIS (Netherlands)

    Rosati, F.; Roelfes, J.G.

    A structure-activity relationship study of the first generation ligands for the DNA-based asymmetric hydration of enones and Diels-Alder reaction in water is reported. The design of the ligand was optimized resulting in a maximum ee of 83% in the hydration reaction and 75% in the Diels-Alder

  4. Structure Investigation of Ti(IV)BODOLates Involved in the Catalytic Asymmetric Reduction of Ketones Using Catecholborane

    DEFF Research Database (Denmark)

    Sarvary, Ian; Norrby, Per-Ola; Frejd, Torbjörn

    2004-01-01

    The complexes formed on mixing Ti(OiPr)4 and bicyclo-octanediols (BODOLs) 1 and 2 (1:1) are useful as chiral catalysts in asymmetric reductions and were investigated by 1HNMR-spectroscopy and by computational methods. A consistent picture emerged of head-to-tail dimers being kept together via a T...

  5. Effects of Mn- and K-addition on catalytic activity of calcium oxide for methane activation

    International Nuclear Information System (INIS)

    Park, Jong Sik; Kong, Jang Il; Lee, Sung Han; Jun, Jong Ho

    1998-01-01

    Pure CaO, Mn-doped CaO, Mn/CaO, and K/CaO catalysts were prepared and tested as catalysts for the oxidative coupling of methane in the temperature range of 600 to 800 .deg. C to investigate the effects of Mn- and K-addition on the catalytic activity of calcium oxide. To characterize the catalysts, X-ray powder diffraction (XRD), XPS, SEM, DSC, and TG analyses were performed. The catalytic reaction was carried out in a single-pass flow reactor using on-line gas chromatography system. Normalized reaction conditions were generally p(CH 4 )/p(O 2 )=250 Torr/50 Torr, total feed flow rate=30 mL/min, and 1 atm of total pressure with He being used as diluent gas. Among the catalysts tested, 6.3 mol% Mn-doped CaO catalyst showed the best C 2 yield of 8.0% with a selectivity of 43.2% at 775 .deg. C. The C 2 selectivity increased on lightly doped CaO catalysts, while decreased on heavily doped CaO((Mn)>6.3 mol%)catalysts. 6 wt.% Mn/CaO and 6 wt.% K/CaO catalysts showed the C 2 selectivities of 13.2% and 30.9%, respectively, for the reaction. Electrical conductivities of CaO and Mn-doped CaO were measured in the temperature range of 500 to 1000 .deg. C at Po2's of 10 -3 to 10 -1 atm. The electrical conductivity was decreased with Mn-doping and increased with increasing Po 2 in the range of 10 -3 to 10 -1 atm, indicating the specimens to be p-type semiconductors. It was suggested that the interstitial oxygen ions formed near the surface can activate methane and the formation of interstitial oxygen ions was discussed on the basis of solid-state chemistry

  6. Dinuclear PhosphoiminoBINOL-Pd Container for Malononitrile: Catalytic Asymmetric Double Mannich Reaction for Chiral 1,3-Diamine Synthesis.

    Science.gov (United States)

    Arai, Takayoshi; Sato, Katsuya; Nakamura, Ayu; Makino, Hiroki; Masu, Hyuma

    2018-01-16

    A phosphoiminoBINOL ligand was designed to form a dinuclear metal complex that could hold a malononitrile molecule. The dinuclear bis(phosphoimino)binaphthoxy-Pd 2 (OAc) 2 complex catalyzed a double Mannich reaction of N-Boc-imines with malononitrile to give chiral 1,3-diamines with high enantioselectivity. The rational asymmetric catalyst, which smoothly introduces the first coupling product to the second coupling reaction while avoiding the reverse reaction, facilitates the over-reaction into a productive reaction process.

  7. Catalytic asymmetric aza-Morita-Baylis-Hillman reaction of methyl acrylate: role of a bifunctional La(O-iPr)3/linked-BINOL complex.

    Science.gov (United States)

    Yukawa, Takafumi; Seelig, Bianca; Xu, Yingjie; Morimoto, Hiroyuki; Matsunaga, Shigeki; Berkessel, Albrecht; Shibasaki, Masakatsu

    2010-09-01

    The catalytic asymmetric aza-Morita-Baylis-Hillman reaction using unactivated methyl acrylate is described. A simple Lewis acidic metal catalyst, such as La(OTf)(3), was not suitable for the reaction, but rare earth metal alkoxide/linked-BINOL complexes possessing bifunctional Lewis acid and Brønsted base properties efficiently promoted the reaction in combination with an achiral nucleophilic organocatalyst. The combined use of a La(O-iPr)(3)/(S,S)-TMS-linked-BINOL complex with a catalytic amount of DABCO promoted the aza-Morita-Baylis-Hillman reaction of a broad range of N-diphenylphosphinoyl imines. Products from aryl, heteroaryl, and alkenyl imines were obtained in 67-99% yield and 81-95% ee. It is noteworthy that isomerizable alkyl imines could be employed as well, giving products in 78-89% yield and 94-98% ee. Initial rate kinetic studies as well as kinetic isotope effect experiments using alpha-deuterio-methyl acrylate support the importance of both the nucleophilicity of La-enolate and the Brønsted basicity of a La-catalyst for promoting the reaction.

  8. Catalytic Asymmetric Mukaiyama-Mannich Reaction of Cyclic C-Acylimines with Difluoroenoxysilanes: Access to Difluoroalkylated Indolin-3-ones.

    Science.gov (United States)

    Li, Jin-Shan; Liu, Yong-Jie; Zhang, Guang-Wu; Ma, Jun-An

    2017-12-01

    A catalytic enantioselective Mukaiyama-Mannich reaction of cyclic C-acylimines with difluoroenoxysilanes is reported. (S)-TRIP enables the enantioselective synthesis of a series of novel difluoroalkylated indolin-3-ones bearing a quaternary stereocenter in up to 97% yield and 98% ee. The synthetic utility of this protocol is highlighted by efficient conversion of the products to the corresponding indolin-3-one derivatives without any erosion of the enantiopurity.

  9. Fabrication of Bi2O3||AC asymmetric supercapacitor with redox additive aqueous electrolyte and its improved electrochemical performances

    International Nuclear Information System (INIS)

    Senthilkumar, S.T.; Selvan, R. Kalai; Ulaganathan, M.; Melo, J.S.

    2014-01-01

    Graphical abstract: An asymmetric supercapacitor (ASC) has been fabricated using α-Bi 2 O 3 and bio-waste derived activated carbon (AC) as negative and positive electrodes respectively with Li 2 SO 4 as electrolyte. Interestingly, the addition of KI into the Li 2 SO 4 electrolyte can significantly enhances the ASC performance through the redox reaction between iodine/iodide ions. -- Highlights: •Flower like α-Bi 2 O 3 is prepared. •An asymmetric supercapacitor is fabricated using α-Bi 2 O 3 as negative electrode and bio-waste derived activated carbon as positive electrode. •Energy density is enhanced from 10.2 Wh kg −1 to 35.4 Wh kg −1 by using KI as redox additive in Li 2 SO 4 electrolyte. -- Abstract: A new asymmetric supercapacitor (ASC) was fabricated using flower like α-Bi2O3as negative and bio-waste derived activated carbon (AC) as positive electrodes with Li2SO4as electrolyte. Here, the fabricated ASC was operated over the potential range of 0-1.6 V and evaluated by cyclic voltammetry (CV), galvano static charge-discharge (GCD), electrochemical impedance spectroscopy (EIS) and cycle life. Further to improve the performance of ASC, KI was used as electrolyte redox additive with pristine (Li2SO4) electrolyte due to their possible redox reactions of iodine ions. Remarkably, a nearly threefold improved specific capacitance and energy density of 99.5 F g −1 and 35.4 Wh kg −1 respectively was achieved by adding of KI into Li 2 SO 4 electrolyte, while it was only 29 F g −1 and 10.2 Wh kg −1 for pristine (Li2SO4) electrolyte used ASC at 1.5 mA cm −2

  10. Catalytic cracking of Arabian Light VGO over novel zeolites as FCC catalyst additives for maximizing propylene yield

    Czech Academy of Sciences Publication Activity Database

    Hussain, A. I.; Aitani, A.; Kubů, Martin; Čejka, Jiří; Al-Khattaf, S.

    2016-01-01

    Roč. 167, MAR 2016 (2016), s. 226-239 ISSN 0016-2361 R&D Projects: GA ČR GBP106/12/G015 Institutional support: RVO:61388955 Keywords : catalytic cracking * FCC additives * 10-ring zeolites Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 4.601, year: 2016

  11. Improving carbon tolerance of Ni-YSZ catalytic porous membrane by palladium addition for low temperature steam methane reforming

    Science.gov (United States)

    Lee, Sang Moon; Won, Jong Min; Kim, Geo Jong; Lee, Seung Hyun; Kim, Sung Su; Hong, Sung Chang

    2017-10-01

    Palladium was added on the Ni-YSZ catalytic porous membrane by wet impregnation and electroless plating methods. Its surface morphology characteristics and carbon deposition properties for the low temperature steam methane reforming were investigated. The addition of palladium could obviously be enhanced the catalytic activity as well as carbon tolerance of the Ni-YSZ porous membrane. The porous membranes were evaluated by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR), CH4 temperature-programmed reduction (CH4-TPR), and O2 temperature-programmed oxidation (O2-TPO). It was found that the Pd-Ni-YSZ catalytic porous membrane showed the superior stability as well as the deposition of carbon on the surface during carbon dissociation adsorption at 650 °C was also suppressed.

  12. Thermodynamically accurate modeling of the catalytic cycle of photosynthetic oxygen evolution: a mathematical solution to asymmetric Markov chains.

    Science.gov (United States)

    Vinyard, David J; Zachary, Chase E; Ananyev, Gennady; Dismukes, G Charles

    2013-07-01

    Forty-three years ago, Kok and coworkers introduced a phenomenological model describing period-four oscillations in O2 flash yields during photosynthetic water oxidation (WOC), which had been first reported by Joliot and coworkers. The original two-parameter Kok model was subsequently extended in its level of complexity to better simulate diverse data sets, including intact cells and isolated PSII-WOCs, but at the expense of introducing physically unrealistic assumptions necessary to enable numerical solutions. To date, analytical solutions have been found only for symmetric Kok models (inefficiencies are equally probable for all intermediates, called "S-states"). However, it is widely accepted that S-state reaction steps are not identical and some are not reversible (by thermodynamic restraints) thereby causing asymmetric cycles. We have developed a mathematically more rigorous foundation that eliminates unphysical assumptions known to be in conflict with experiments and adopts a new experimental constraint on solutions. This new algorithm termed STEAMM for S-state Transition Eigenvalues of Asymmetric Markov Models enables solutions to models having fewer adjustable parameters and uses automated fitting to experimental data sets, yielding higher accuracy and precision than the classic Kok or extended Kok models. This new tool provides a general mathematical framework for analyzing damped oscillations arising from any cycle period using any appropriate Markov model, regardless of symmetry. We illustrate applications of STEAMM that better describe the intrinsic inefficiencies for photon-to-charge conversion within PSII-WOCs that are responsible for damped period-four and period-two oscillations of flash O2 yields across diverse species, while using simpler Markov models free from unrealistic assumptions. Copyright © 2013 Elsevier B.V. All rights reserved.

  13. Using spent fluid catalytic cracking (FCC catalyst as pozzolanic addition — a review

    Directory of Open Access Journals (Sweden)

    Nancy Torres Castellanos

    2010-05-01

    Full Text Available Spent fluid catalytic cracking (FCC catalyst is an oil industry by product from fluidised-bed catalytic cracking units. This residue is mainly formed by an active component (faujasite type zeolite Y in an amorphous aluminosilicate matrix. It mainly consists of up to 90% silica and alumina. This paper reports an extensive literature review regarding the characterisation and mechanical and durability properties of mortar and concrete added to this material. FCC has been studied lately due to its pozzolanic characteristics and the good performance of concrete mixtures using FCC as cement replacement.

  14. Catalytic effect of additional metallic phases on the hydrogen absorption behavior of a Zr-Based alloy

    International Nuclear Information System (INIS)

    Ruiz, F; Peretti, H; Castro, E; Real, S; Visitin, A; Triaca, W

    2005-01-01

    The electrochemical hydrogen absorption of electrodes containing Zr 0 .9Ti 0 .1(Ni 0 .5Mn 0 .25Cr 0 .20V 0 .05) 2 is studied in alkaline media by monitoring the activation and discharge capacity along charge-discharge cycling.The considered alloy is tested in both as melted and annealed condition in order to investigate the catalytic effect of small amounts of micro segregated secondary phases of the Zr-Ni system. Since these catalytic phases are only present in the as melted alloys, tests are also carried out using a composite material elaborated from powders of the annealed alloy with the addition of 18 wt.% of the suspected catalytic phases, melted separately.The hydrogen absorption-desorption behavior for the different cases is discussed and correlated with the metallurgical characterization of the materials.The catalytic effects are studied employing cyclic voltammetry and electrochemical impedance techniques. The results are analyzed in terms of a developed physicochemical model

  15. Stochastic resonance in an asymmetric bistable system driven by multiplicative colored noise and additive white noise

    International Nuclear Information System (INIS)

    Zhou Bingchang; Xu Wei

    2008-01-01

    The phenomenon of stochastic resonance (SR) in a bistable system driven by multiplicative colored and additive white noises and a periodic rectangular signal with a constant component is studied by using the unified colored noise approximation and the theory of signal-to-noise (SNR) in the adiabatic limit. The analytic expression of the SNR is obtained for arbitrary signal amplitude without being restricted to small amplitudes. The SNR is a non-monotonic function of intensities of multiplicative colored and additive white noises and correlation time of multiplicative colored noise, so SR exhibits in the bistable system. The effects of potential asymmetry r and correlation time τ of multiplicative colored noise on SNR are opposite. Moreover, It is more sensitive to control SR through adjusting the additive white noise intensity D than adjusting the multiplicative colored noise intensity Q

  16. Mechanism for the regioselective asymmetric addition of grignard reagents to malimides: A computational exploration.

    Science.gov (United States)

    Ye, Jian-Liang; Huang, Pei-Qiang; Lu, Xin

    2007-01-05

    We present a systematic theoretical investigation on the addition reaction of Grignard reagents to malimides to understand its mechanism as well as the origin of its regio- and diastereo-selectivity. The computations carried out at a hybrid density functional B3LYP/6-31G* level of theory reveal that (i) the addition of Grignard reagents with N,O-dimethylmalimide (1-methyl-3-methoxypyrrolidine-2,5-dione) occurs regioselectively at the alpha-carbonyl (C1) by passing through a cis-alpha-chelated precursor and affords stereoselectively cis-addition product, in qualitative agreement with the previous experimental observations; (ii) such regioselectivity is ascribed to the preferential chelation of Grignard reagent to the alpha-carbonyl (C1) over the coordination to the alpha-carbonyl (C4); (iii) its unusual trans-addition, in sharp contrast to the Cram chelation-type stereoselectivity for the reaction of aliphatic alpha- or beta-alkoxy carbonyl compounds, is due primarily to the rigidity of the five-membered ring skeleton of the malimide that favors the formation of the cis-alpha-chelated precursor; and (iv) poor regioselectivity is predicted for the reaction of O-TBDMS-protected malimide (1-benzyl-3-(tert-butyldimethylsilyloxy)pyrrolidine-2,5-dione) with Grignard reagent and can be ascribed to the large steric repulsion of the bulky TBDMS group and the electronic effects of the silyl group that remarkably destabilizes the alpha-chelated precursors and the corresponding transition states.

  17. Phosphine-Catalyzed Asymmetric Umpolung Addition of Trifluoromethyl Ketimines to Morita-Baylis-Hillman Carbonates.

    Science.gov (United States)

    Chen, Peng; Yue, Zhenting; Zhang, Junyou; Lv, Xi; Wang, Lei; Zhang, Junliang

    2016-10-10

    A novel phosphine-catalyzed, highly enantioselective umpolung addition of trifluoromethyl ketimines to Morita-Baylis-Hillman carbonates was developed and it provides facile access to optically active trifluoromethyl amines with a chiral tertiary stereocenter under mild reaction conditions. The salient features of this reaction include general substrate scope, mild reaction conditions, good yields, high enantioselectivity, ease of scale-up to gram scale, and further transformations of the products. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Characterization and mechanism insight of accelerated catalytic promiscuity of Sulfolobus tokodaii (ST0779) peptidase for aldol addition reaction.

    Science.gov (United States)

    Li, Rong; Perez, Bianca; Jian, Hui; Jensen, Mads Mørk; Gao, Renjun; Dong, Mingdong; Glasius, Marianne; Guo, Zheng

    2015-11-01

    A novel peptidase from thermophilic archaea Sulfolobus tokodaii (ST0779) is examined for its catalytic promiscuity of aldol addition, which shows comparable activity as porcine pancreatic lipase (PPL, one of the best enzymes identified for biocatalytic aldol addition) at 30 °C but much accelerated activity at elevated temperature. The molecular catalytic efficiency kcat/Km (M(-1) s(-1)) of this thermostable enzyme at 55 °C adds up to 140 times higher than that of PPL at its optimum temperature 37 °C. The fluorescence quenching analysis depicts that the binding constants of PPL are significantly higher than those of ST0779, and their numbers of binding sites show opposite temperature dependency. Thermodynamic parameters estimated by fluorescence quenching analysis unveil distinctly different substrate-binding modes between PPL and ST0779: the governing binding interaction between PPL and substrates is hydrophobic force, while the dominating substrate-binding forces for ST0779 are van der Waals and H-bonds interactions. A reasonable mechanism for ST0779-catalyzed aldol reaction is proposed based on kinetic study, spectroscopic analysis, and molecular stereostructure simulation. This work represents a successful example to identify a new enzyme for catalytic promiscuity, which demonstrates a huge potential to discover and exploit novel biocatalyst from thermophile microorganism sources.

  19. Production of aromatic green gasoline additives via catalytic pyrolysis of acidulated peanut oil soap stock.

    Science.gov (United States)

    Hilten, R; Speir, R; Kastner, J; Das, K C

    2011-09-01

    Catalytic pyrolysis was used to generate gasoline-compatible fuel from peanut oil soap stock (PSS), a high free fatty acid feedstock, using a fixed-bed reactor at temperatures between 450 and 550°C with a zeolite catalyst (HZSM-5). PSS fed at 81 gh(-1) along with 100 mL min(-1) inert gas was passed across a 15 g catalyst bed (WHSV=5.4h(-1), gas phase residence time=34s). Results indicate that fuel properties of PSS including viscosity, heating value, and O:C ratio were improved significantly. For PSS processed at 500°C, viscosity was reduced from 59.6 to 0.9 mm(2)s(-1), heating value was increased from 35.8 to 39.3 MJL(-1), and the O:C ratio was reduced from 0.07 to 0.02. Aromatic gasoline components (e.g., BTEX), were formed in concentrations as high as 94% (v/v) in catalytically-cracked PSS with yields ranging from 22% to 35% (v/v of PSS feed). Copyright © 2011 Elsevier Ltd. All rights reserved.

  20. Catalytic Asymmetric Synthesis of 3-Indolyl Methanamines Using Unprotected Indoles and N-Boc Imines under Basic Conditions.

    Science.gov (United States)

    Arai, Takayoshi; Kakino, Junki

    2016-12-05

    A chiral imidazolidine-containing NCN/Pd-OTf catalyst (C4) promoted the nucleophilic addition of unprotected indoles to N-Boc imines. Using sulfinyl amines as the N-Boc imine precursors, the combined use of C4 with K 2 CO 3 activated the NH indoles to give chiral 3-indolyl methanamines with up to 98 % ee. Compared with conventional acid-catalyzed Friedel-Crafts reactions, this reaction proceeds under mildly basic conditions and is advantageous for the use of acid-sensitive substrates. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Lewis base activation of Lewis acids: catalytic, enantioselective addition of glycolate-derived silyl ketene acetals to aldehydes.

    Science.gov (United States)

    Denmark, Scott E; Chung, Won-Jin

    2008-06-20

    A catalytic system involving silicon tetrachloride and a chiral, Lewis basic bisphosphoramide catalyst is effective for the addition of glycolate-derived silyl ketene acetals to aldehydes. It was found that the sense of diastereoselectivity could be modulated by changing the size of the substituents on the silyl ketene acetals. In general, the trimethylsilyl ketene acetals derived from methyl glycolates with a large protecting group on the alpha-oxygen provide enantiomerically enriched alpha,beta-dihydroxy esters with high syn-diastereoselectivity, whereas the tert-butyldimethylsilyl ketene acetals derived from bulky esters of alpha-methoxyacetic acid provide enantiomerically enriched alpha,beta-dihydroxy esters with high anti-diastereoselecitvity.

  2. Role of Regioisomeric Bicyclo[3.3.0]octa-2,5-diene Ligands in Rh Catalysis: Synthesis, Structural Analysis, Theoretical Study, and Application in Asymmetric 1,2- and 1,4-Additions.

    Science.gov (United States)

    Mühlhäuser, Tina; Savin, Alex; Frey, Wolfgang; Baro, Angelika; Schneider, Andreas J; Döteberg, Heinz-Günter; Bauer, Florian; Köhn, Andreas; Laschat, Sabine

    2017-12-15

    In order to study the impact of regioisomeric diene ligands on the formation and catalytic activity of Rh complexes, a series of C 2 - and C S -symmetric 2,5-disubstituted bicyclo[3.3.0]octa-2,5-dienes C 2 -L and C S -L, respectively, were synthesized from Weiss diketone by simultaneous deprotonation/electrophilic trapping of both oxo functions, and the catalytic behavior was studied in the presence of [RhCl(C 2 H 4 ) 2 ] 2 . Complexes [RhCl(C 2 -L)] 2 bearing C 2 -symmetric ligands catalyzed effectively the asymmetric arylation of N-tosylaldimines to (S)-diarylamines with yields and ee values up to 99%. In Hayashi-Miyaura reactions, however, the complexes showed poor catalytic activity. When complexes [RhCl(C S -L)] 2 with C S -symmetric ligand or mixtures of [RhCl(C 2 -L)] 2 and [RhCl(C S -L)] 2 were employed in 1,2-additions, racemic addition products were observed, suggesting a C═C isomerization of the diene ligands. X-ray crystal structure analysis of both Rh complexes formed from the [RhCl(C 2 H 4 ) 2 ] 2 precursor and ligands C 2 -L and C S -L revealed that only the C 2 -symmetric ligand C 2 -L coordinated to the Rh, whereas C S -L underwent a Rh-catalyzed C═C isomerization to rac-C 2 -L, which then gave the racemic [RhCl(rac-C 2 -L)] 2 complex. DFT calculations of the relative stabilities of the Rh complexes and the proposed intermediates provided a mechanistic rationale via Rh-mediated hydride transfer.

  3. Reaction phenomena of catalytic partial oxidation of methane under the impact of carbon dioxide addition and heat recirculation

    International Nuclear Information System (INIS)

    Chen, Wei-Hsin; Lin, Shih-Cheng

    2015-01-01

    The reaction phenomena of CPOM (catalytic partial oxidation of methane) in a Swiss-roll reactor are studied numerically where a rhodium-based catalyst bed is embedded at the center of the reactor. CO 2 is added into the feed gas and excess enthalpy recovery is performed to evaluate their influences on CPOM performance. In the study, the mole ratio of O 2 to CH 4 (O 2 /CH 4 ratio) is fixed at 0.5 and the mole ratio of CO 2 to O 2 (CO 2 /O 2 ratio) is in the range of 0–2. The results reveal that CO 2 addition into the influent has a slight effect on methane combustion, but significantly enhances dry reforming and suppresses steam reforming. The reaction extents of steam reforming and dry reforming in CPOM without heat recovery and CO 2 addition are in a comparable state. Once CO 2 is added into the feed gas, the dry reforming is enhanced, thereby dominating CH 4 consumption. Compared to the reactor without excess enthalpy recovery, heat recirculation drastically increases the maximum reaction temperature and CH 4 conversion in the catalyst bed; it also intensifies the H 2 selectivity, H 2 yield, CO 2 conversion, and syngas production rate. The predictions indicate that the heat recirculation is able to improve the syngas formation up to 45%. - Highlights: • Catalytic partial oxidation of methane with CO 2 addition and heat recovery is studied. • CO 2 addition has a slight effect on methane combustion. • CO 2 addition significantly enhances dry reforming and suppresses steam reforming. • Dry reforming dominates CH 4 consumption when CO 2 addition is large. • Heat recirculation can improve the syngas formation up to 45%

  4. A new continuous-flow process for catalytic conversion of glycerol to oxygenated fuel additive: Catalyst screening

    International Nuclear Information System (INIS)

    Nanda, Malaya R.; Yuan, Zhongshun; Qin, Wensheng; Ghaziaskar, Hassan S.; Poirier, Marc-Andre; Xu, Chunbao

    2014-01-01

    Highlights: • A continuous-flow process for catalytic synthesis of solketal from glycerol. • Six different heterogeneous acid catalysts were studied in the process. • Glycerol conversion and solketal yield of 90% and 88% respectively were achieved. • The process has the potential to be scaled-up for industrial applications. - Abstract: A new continuous-flow reactor was designed for the conversion of glycerol to solketal, an oxygenated fuel additive, through ketalization with acetone. Six heterogeneous catalysts were investigated with respect to their catalytic activity and stability in a flow reactor. The acidity of the catalysts positively influences the catalyst’s activity. Among all the solid acid catalysts tested, the maximum solketal yield from experiments at 40 °C, 600 psi and WHSV of 4 h −1 attained 73% and 88% at the acetone/glycerol molar ratio of 2.0 and 6.0, respectively, with Amberlyst Wet. Based on the solketal yield and glycerol conversion results, the activity of all catalysts tested follows the following order of sequence: Amberlyst Wet ≈ Zeolite ≈ Amberlyst Dry > Zirconium Sulfate > Montmorillonite > Polymax. An increase in acetone/glycerol molar ratio or a decrease in WHSV enhanced the glycerol conversion as expected. This process offers an attractive route for converting glycerol, the main by-product of biodiesel, to solketal – a value-added green product with potential industrial applications as a valuable fuel additive or combustion promoter for gasoline engines

  5. Catalytic enantioselective conjugate addition of diethylzinc using NiII-DAIB complexes

    NARCIS (Netherlands)

    Jansen, Johan F.G.A.; Feringa, Bernard

    The conjugate addition of diethylzinc to chalcone, catalyzed by a NiII complex of the chiral aminoalcohol (-)-DAIB, resulted in the formation of (R)-1,3-diphenyl-penta-1-one with enantiomeric excess up to 85%.

  6. A study of catalytic behaviour of aromatic additives on the photo ...

    Indian Academy of Sciences (India)

    Administrator

    red using photo–. Fenton reaction. The progress of the reaction has been monitored spectrophotometrically. The effect of various organic additives e.g. hydroquinone, resorcinol and catechol on the rate of photodegradation has been observed.

  7. Lewis base activation of Lewis acids: catalytic, enantioselective vinylogous aldol addition reactions.

    Science.gov (United States)

    Denmark, Scott E; Heemstra, John R

    2007-07-20

    The generality of Lewis base catalyzed, Lewis acid mediated, enantioselective vinylogous aldol addition reactions has been investigated. The combination of silicon tetrachloride and chiral phosphoramides is a competent catalyst for highly selective additions of a variety of alpha,beta-unsaturated ketone-, 1,3-diketone-, and alpha,beta-unsaturated amide-derived dienolates to aldehydes. These reactions provided high levels of gamma-site selectivity for a variety of substitution patterns on the dienyl unit. Both ketone- and morpholine amide-derived dienol ethers afforded high enantio- and diastereoselectivity in the addition to conjugated aldehydes. Although alpha,beta-unsaturated ketone-derived dienolate did not react with aliphatic aldehydes, alpha,beta-unsaturated amide-derived dienolates underwent addition at reasonable rates affording high yields of vinylogous aldol product. The enantioselectivities achieved with the morpholine derived-dienolate in the addition to aliphatic aldehydes was the highest afforded to date with the silicon tetrachloride-chiral phosphoramide system. Furthermore, the ability to cleanly convert the morpholine amide to a methyl ketone was demonstrated.

  8. CATALYTIC ENANTIOSELECTIVE CONJUGATE ADDITION OF DIETHYLZINC USING NI(II) DAIB COMPLEXES

    NARCIS (Netherlands)

    JANSEN, JFGA; FERINGA, BL

    The conjugate addition of diethylzinc to chalcone, catalyzed by a NiII complex of the chiral amino-alcohol (-)-DAIB, resulted in the formation of (R)-1,3-diphenyl-penta-1-one with enantiomeric excess up to 85%.

  9. Catalytic cracking of vacuum gasoil overSVR, ITH, and MFI zeolites as FCC catalyst additives

    Czech Academy of Sciences Publication Activity Database

    Hussain, A. I.; Palani, A.; Aitani, A. M.; Čejka, Jiří; Shamzhy, Mariya; Kubů, Martin; Al-Khattaf, S. S.

    2017-01-01

    Roč. 161, JUN 2017 (2017), s. 23-32 ISSN 0378-3820 R&D Projects: GA ČR GBP106/12/G015; GA ČR(CZ) GP14-30898P Institutional support: RVO:61388955 Keywords : ith * mfi * Light olefins * FCC additives Subject RIV: CF - Physical ; Theoretical Chemistry OBOR OECD: Physical chemistry Impact factor: 3.752, year: 2016

  10. Kinetic resolution of hindered Morita-Baylis-Hillman adducts by Rh(I)-catalyzed asymmetric 1,4-addition/β-hydroxyelimination.

    Science.gov (United States)

    Wang, Yazhou; Feng, Xiangqing; Du, Haifeng

    2011-09-16

    A kinetic resolution of hindered Morita-Baylis-Hillman adducts has been successfully achieved in excellent selectivities via Rh(I)-catalyzed asymmetric 1,4-addition/β-hydroxyelimination with the use of a chiral sulfinamide/olefin hybrid ligand. This study provides a novel and efficient access to both optically active hindered highly functionalized alkenes and Morita-Baylis-Hillman adducts. © 2011 American Chemical Society

  11. Molybdenum-based additives to mixed-metal oxides for use in hot gas cleanup sorbents for the catalytic decomposition of ammonia in coal gases

    Science.gov (United States)

    Ayala, Raul E.

    1993-01-01

    This invention relates to additives to mixed-metal oxides that act simultaneously as sorbents and catalysts in cleanup systems for hot coal gases. Such additives of this type, generally, act as a sorbent to remove sulfur from the coal gases while substantially simultaneously, catalytically decomposing appreciable amounts of ammonia from the coal gases.

  12. Performance under sulfate attack of concrete additioned with fluid catalytic cracking catalyst residue (FCC and metakaolin (MK

    Directory of Open Access Journals (Sweden)

    Nancy Torres Castellanos

    2013-01-01

    Full Text Available In this work the evaluation of the performance of concrete added with Fluid Catalytic Cracking Catalyst residue (FCC from a Colombian petroleum company, under sulfate attack, is presented. The results of this concrete are compared with the results of Metakaolin (MK added concrete. The analysis of the pozzolanic materials included the determination of the particle size, the pozzolanic activity and the chemical and mineralogical composition. Different percentages of FCC were used as Portland cement replacement in proportions of 0, 10, 20 and 30%; similarly concrete added with 20% of MK as replacement was elaborated. Compressive strength and performance under sulfate attack were evaluated. Results showed that concrete with FCC and MK as well as control concrete had similar behavior; however its expansion was higher. In addition, the performance of the two types of concrete (FCC y MK under sulfate attack was comparable; this could be due to fact that FCC and MK showed similarities regarding of their chemical and mineralogical composition. Importantly, after 360 days of exposure the specimens with MK and FCC showed no significant deterioration.

  13. A review of recent advances on the effects of microstructural refinement and nano-catalytic additives on the hydrogen storage properties of metal and complex hydrides

    Energy Technology Data Exchange (ETDEWEB)

    Varin, R. A.; Zbroniec, L. [University of Waterloo, Department of Mechanical and Mechatronics Engineering, Waterloo, Ontario (Canada); Polanski, M.; Bystrzycki, J. [Faculty of Advanced Technology and Chemistry, Military University of Technology, Warsaw (Poland)

    2011-07-01

    The recent advances on the effects of microstructural refinement and various nano-catalytic additives on the hydrogen storage properties of metal and complex hydrides obtained in the last few years in the allied laboratories at the University of Waterloo (Canada) and Military University of Technology (Warsaw, Poland) are critically reviewed in this paper. The research results indicate that microstructural refinement (particle and grain size) induced by ball milling influences quite modestly the hydrogen storage properties of simple metal and complex metal hydrides. On the other hand, the addition of nanometric elemental metals acting as potent catalysts and/or metal halide catalytic precursors brings about profound improvements in the hydrogen absorption/desorption kinetics for simple metal and complex metal hydrides alike. In general, catalytic precursors react with the hydride matrix forming a metal salt and free nanometric or amorphous elemental metals/intermetallics which, in turn, act catalytically. However, these catalysts change only kinetic properties i.e. the hydrogen absorption/desorption rate but they do not change thermodynamics (e.g., enthalpy change of hydrogen sorption reactions). It is shown that a complex metal hydride, LiAlH{sub 4}, after high energy ball milling with a nanometric Ni metal catalyst and/or MnCl{sub 2} catalytic precursor, is able to desorb relatively large quantities of hydrogen at room temperature, 40 and 80 {sup o}C. This kind of behavior is very encouraging for the future development of solid state hydrogen systems. (authors)

  14. Asymmetric Carbamoyl Anion Additions to Chiral N-Phosphonyl Imines via the GAP Chemistry Process and Stereoselectivity Enrichments.

    Science.gov (United States)

    Seifert, Cole W; Pindi, Suresh; Li, Guigen

    2015-01-02

    Carbamoyl anions were found to smoothly react with chiral N-phosphonyl imines in toluene at -78 °C to r.t. using LiHMDS as the base. Group-assisted purification (GAP) has been utilized to give the pure amides without using column chromatography or recrystallization. The asymmetric reaction resulted in chiral N-phosphonyl amino amides with good to excellent yields (71-99%) and good crude diastereoselectivities (dr 84:16-95:5). In this GAP procedure, the crude solids are washed with diethyl ether to afford the pure products, as revealed by (1)H NMR analysis; GAP washing consistently increases the diastereopurity of the products, resulting in excellent diastereoselectivities, often with final dr > 99:1. Interestingly, the diastereoenriched products can be obtained either in the ether solution or as the suspended solid, depending on the substrate.

  15. Promoting Effect of CeO2 Addition on Activity and Catalytic Stability in Steam Reforming of Methane over Ni/Al2O3

    International Nuclear Information System (INIS)

    Rakib, A.; Gennequin, C.; Ringot, S.; Aboukais, A.; Abi-Aad, E.; Dhainaut, T.

    2011-01-01

    Hydrogen production by steam reforming of methane was studied over Ni catalysts supported on CeO 2 , Al 2 O 3 and CeO 2 -Al 2 O 3 . These catalysts were prepared using the impregnation method and characterized by XRD. The effect of CeO2 promoter on the catalytic performance of Ni/Al 2 O 3 catalyst for methane steam reforming reaction was investigated. In fact, CeO 2 had a positive effect on the catalytic activity in this reaction. Experimental results demonstrated that Ni/CeO 2 -Al 2 O 3 catalyst showed excellent catalytic activity and high reaction performance. In addition, the effects of reaction temperature and metal content on the conversion of CH 4 and H 2 /CO ratio were also investigated. Results indicated that CH4 conversion increased significantly with the increase of the reaction temperature and metal content. (author)

  16. Effect of redox additives over Ni/Al{sub 2}O{sub 3} catalysts on syngas production via methane catalytic partial oxidation

    Energy Technology Data Exchange (ETDEWEB)

    J. Requies; V.L. Barrio; J.F. Cambra; M.B. Guemez; P.L. Arias; V. La Parola; M.A. Pena; J.L.G. Fierro [University of the Basque Country, Bilbao (Spain). School of Engineering

    2008-11-15

    Alumina-supported nickel catalysts modified with redox (Mo, Mn and Sn) oxides were tested in the catalytic partial oxidation (CPO) of methane and the wet catalytic partial oxidation (wet-CPO) of methane for syngas production. The influence of different reaction parameters on the performance of these systems was studied for both reactions. Certain insights on catalyst surface structure were revealed by means of X-ray photoelectron spectroscopy (XPS) and thermal programmed reduction (TPR). The joint analysis of all the results led to certain correlations between the structure of the catalysts and catalytic activity, indicating that the redox additives to some extent modify the stability of the active nickel phase by altering the nickel-alumina interface interaction. 37 refs., 9 figs., 4 tabs.

  17. Radiochemical methods and spectroscopical analyses for investigating the catalytic effects of 2-methyltetrahydro-anthraquinone and phenanthraquinone in wood pulp production using the soda additive method

    International Nuclear Information System (INIS)

    Besser, R. v.

    1982-01-01

    The studies were to show whether 2-methyltetrahydroanthraquinone or phenanthraquinone, two additives obtainable at low cost, will have a suitable catalytic effect on the delignification using the soda additive pulping method. For this purpose, soda cookings have been made in a 7 l rotary autoclave. The results have shown that 2-MeTHAQ is by far the better catalytic agent. Further experiments have been made to investigate the mode of action of the redox additives, intended to reveal further characteristics which can be correlated with the knowledge obtained from the preceding soda cookings. The analysis shows that there is a connection between the analytical lignin characteristics and the effectiveness of quinoid additives. (orig./PW) [de

  18. Asymmetric fluorocyclizations of alkenes.

    Science.gov (United States)

    Wolstenhulme, Jamie R; Gouverneur, Véronique

    2014-12-16

    CONSPECTUS: The vicinal fluorofunctionalization of alkenes is an attractive transformation that converts feedstock olefins into valuable cyclic fluorinated molecules for application in the pharmaceutical, agrochemical, medical, and material sectors. The challenges associated with asymmetric fluorocyclizations induced by F(+) reagents are distinct from other types of halocyclizations. Processes initiated by the addition of an F(+) reagent onto an alkene do not involve the reversible formation of bridged fluoronium ions but generate acyclic β-fluorocationic intermediates. This mechanistic feature implies that fluorocyclizations are not stereospecific. A discontinuity exists between the importance of this class of fluorocyclization and the activation modes currently available to implement successful catalysis. Progress toward fluorocyclization has been achieved by investing in neutral and cationic [NF] reagent development. The body of work on asymmetric fluorination using chiral cationic [NF](+) reagents prepared by fluorine transfer from the dicationic [NF](2+) reagent Selectfluor to quinuclidines, inspired the development of asymmetric F(+)-induced fluorocyclizations catalyzed by cinchona alkaloids; for catalysis, the use of N-fluorobenzenesulfonimide, which is less reactive than Selectfluor, ensures that the achiral F(+) source remains unreactive toward the alkene. These organocatalyzed enantioselective fluorocyclizations can be applied to indoles to install the fluorine on a quaternary benzylic stereogenic carbon center and to afford fluorinated analogues of natural products featuring the hexahydropyrrolo[2,3-b]indole or the tetrahydro-2H-furo[2,3-b]indole skeleton. In an alternative approach, the poor solubility of dicationic Selectfluor bis(tetrafluoroborate) in nonpolar solvent was exploited with anionic phase transfer catalysis as the operating activation mode. Exchange of the tetrafluoroborate ions of Selectfluor with bulky lipophilic chiral anions (e

  19. Chemoselective Switch in the Asymmetric Organocatalysis of 5 H -Oxazol-4-ones and N -Itaconimides: Addition-Protonation or [4+2] Cycloaddition

    KAUST Repository

    Zhu, Bo

    2015-12-09

    © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. We report a synthetic strategy for a chemoselective switch and a diastereo-divergent approach for the asymmetric reaction of 5H-oxazol-4-ones and N-itaconimides catalyzed by L-tert-leucine-derived tertiary amine-urea compounds. The reaction was modulated to harness either tandem conjugate addition-protonation or [4+2] cycloaddition as major product with excellent enantio- and diastereoselectivities. Subjecting the enantio-enriched cycloaddition products to a basic silica gel reagent yields the diastereomer vis-à-vis the product directly obtained under conditions for addition-protonation, thus opening a diastereo-divergent route for creating 1,3-tertiary-hetero-quaternary stereocenters. Quantum chemical studies further provide stereochemical analysis for the [4+2] process and a plausible mechanism for this chemoselective switch is proposed.

  20. Asymmetric Synthesis of exo-Isobrevicomin and exo-Brevicomin via Conjugated Addition of Primary Alkyl Iodides to a,b-Unsaturated Ketones

    Directory of Open Access Journals (Sweden)

    Sousa Andréa L. de

    2002-01-01

    Full Text Available (--exo-Isobrevicomin (1 and (+-exo-brevicomin (2 are volatile substances produced by males of the beetles Dendroctonus ponderosae, which inhabit pine trees found in the northern hemisphere, frequently causing the death of their host. In order to obtain these aggregation pheromones, which present the 6,8-dioxabicyclo[3.2.1]octane structure, the synthetic strategies utilized in this work had as key steps the Sharpless asymmetric dihydroxylation and the conjugated addition, promoted by the Zn(Cu couple in aqueous medium and accelerated by ultrasound. The conjugated addition of acetonides 13 and 14 to the respective unsaturated ketones (methyl vinyl ketone and ethyl vinyl ketone furnished the adducts 15 and 16. The intramolecular catalyzed cyclization of compounds 15 and 16 with phosphotungstic acid (H3PW12O40 produced exo-isobrevicomin (1 and exo-brevicomin (2.

  1. Asymmetric synthesis of syn-propargylamines and unsaturated β-amino acids under Brønsted base catalysis

    Science.gov (United States)

    Wang, Yingcheng; Mo, Mingjie; Zhu, Kongxi; Zheng, Chao; Zhang, Hongbin; Wang, Wei; Shao, Zhihui

    2015-01-01

    Propargylamines are important intermediates for the synthesis of polyfunctional amino derivatives and natural products and biologically active compounds. The classic method of synthesizing chiral propargylamines involves the asymmetric alkynylation of imines. Here, we report a significant advance in the catalytic asymmetric Mannich-type synthesis of propargylamines through catalytic asymmetric addition of carbon nucleophiles to C-alkynyl imines, culminating in a highly syn-selective catalytic asymmetric Mannich reaction of C-alkynyl imines that provide syn-configured propargylamines with two adjacent stereogenic centres and a transition metal-free organocatalytic asymmetric approach to β-alkynyl-β-amino acids with high efficiency and practicality, via a chiral Brønsted base-catalysed asymmetric Mannich-type reaction of in situ generated challenging N-Boc C-alkynyl imines from previously unreported C-alkynyl N-Boc-N,O-acetals, with α-substituted β-keto esters and less-acidic malonate (thio)esters as nucleophiles, respectively. A catalytic activation strategy is also disclosed, which may have broad implications for use in catalysis and synthesis. PMID:26423837

  2. Hydrodehalogenation of alkyl iodides with base-mediated hydrogenation and catalytic transfer hydrogenation: application to the asymmetric synthesis of N-protected α-methylamines.

    Science.gov (United States)

    Mandal, Pijus K; Birtwistle, J Sanderson; McMurray, John S

    2014-09-05

    We report a very mild synthesis of N-protected α-methylamines from the corresponding amino acids. Carboxyl groups of amino acids are reduced to iodomethyl groups via hydroxymethyl intermediates. Reductive deiodination to methyl groups is achieved by hydrogenation or catalytic transfer hydrogenation under alkaline conditions. Basic hydrodehalogenation is selective for the iodomethyl group over hydrogenolysis-labile protecting groups, such as benzyloxycarbonyl, benzyl ester, benzyl ether, and 9-fluorenyloxymethyl, thus allowing the conversion of virtually any protected amino acid into the corresponding N-protected α-methylamine.

  3. Asymmetric Ion-Pairing Catalysis

    Science.gov (United States)

    Brak, Katrien

    2014-01-01

    Charged intermediates and reagents are ubiquitous in organic transformations. The interaction of these ionic species with chiral neutral, anionic, or cationic small molecules has emerged as a powerful strategy for catalytic, enantioselective synthesis. This review describes developments in the burgeoning field of asymmetric ion-pairing catalysis with an emphasis on the insights that have been gleaned into the structural and mechanistic features that contribute to high asymmetric induction. PMID:23192886

  4. Multicatalyst system in asymmetric catalysis

    CERN Document Server

    Zhou, Jian

    2014-01-01

    This book introduces multi-catalyst systems by describing their mechanism and advantages in asymmetric catalysis.  Helps organic chemists perform more efficient catalysis with step-by-step methods  Overviews new concepts and progress for greener and economic catalytic reactions  Covers topics of interest in asymmetric catalysis including bifunctional catalysis, cooperative catalysis, multimetallic catalysis, and novel tandem reactions   Has applications for pharmaceuticals, agrochemicals, materials, and flavour and fragrance

  5. Effect of Manganese Additive on the Improvement of Low-Temperature Catalytic Activity of VO(x)-WO(x)/TiO2 Nanoparticles for Chlorobenzene Combustion.

    Science.gov (United States)

    He, Fei; Chen, Chunxiao; Liu, Shantang

    2016-06-01

    In this study, V-W/TiO2, Mn-V-W/TiO2 and Mn-W/TiO2 nanoparticles were prepared by homogeneous precipitation method and investigated for the catalytic combustion of chlorobenzene (CB), which was used as a model compound of chlorinated volatile organic compounds (CVOCs). The samples were characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption, transmission electron microscope (TEM) and hydrogen temperature-programed reduction (H2-TPR). The average size of the nanoparticles was -20 nm. Manganese species were evenly distributed on the surface of the V-W/TiO2 catalyst, and a small amount of manganese addition did not affect the crystal form, crystallinity and morphology of the V-W/TiO2 catalyst. In addition, low-temperature catalytic activity of V-W/TiO2 catalysts could be effectively improved. When the molar ratio of Mn/(Mn + V) was 0.25 or 0.4, the catalyst displayed the highest low-temperature activity. This was possibly due to Mn (VO3)x formed by the reaction of manganese and vanadium species. Meanwhile, we also found that the addition of oxalic acid was benefit to the improvement of the catalytic activities. When manganese content was high, such as Mn (0.75) VW/Ti, the catalyst activity declined seriously, and the reason was also discussed.

  6. Asymmetric synthesis of α-amino acids via homologation of Ni(II) complexes of glycine Schiff bases. Part 3: Michael addition reactions and miscellaneous transformations.

    Science.gov (United States)

    Aceña, José Luis; Sorochinsky, Alexander E; Soloshonok, Vadim

    2014-09-01

    The major goal of this review is a critical discussion of the literature data on asymmetric synthesis of α-amino acids via Michael addition reactions involving Ni(II)-complexes of amino acids. The material covered is divided into two conceptually different groups dealing with applications of: (a) Ni(II)-complexes of glycine as C-nucleophiles and (b) Ni(II)-complexes of dehydroalanine as Michael acceptors. The first group is significantly larger and consequently subdivided into four chapters based on the source of stereocontrolling element. Thus, a chiral auxiliary can be used as a part of nucleophilic glycine Ni(II) complex, Michael acceptor or both, leading to the conditions of matching vs. mismatching stereochemical preferences. The particular focus of the review is made on the practical aspects of the methodology under discussion and mechanistic considerations.

  7. Indium-mediated asymmetric barbier-type allylations: additions to aldehydes and ketones and mechanistic investigation of the organoindium reagents.

    Science.gov (United States)

    Haddad, Terra D; Hirayama, Lacie C; Singaram, Bakthan

    2010-02-05

    We report a simple, efficient, and general method for the indium-mediated enantioselective allylation of aromatic and aliphatic aldehydes and ketones under Barbier-type conditions in a one-pot synthesis affording the corresponding chiral alcohol products in very good yield (up to 99%) and enantiomeric excess (up to 93%). Our method is able to tolerate various functional groups, such as esters, nitriles, and phenols. Additionally, more substituted allyl bromides, such as crotyl and cinnamyl bromide, can be used providing moderate enantioselectivity (72% and 56%, respectively) and excellent diastereoselectivity when employing cinnamyl bromide (>95/5 anti/syn). However, the distereoselectivity when using crotyl bromide was poor and other functionalized allyl bromides under our method afforded low enantioselectivities for the alcohol products. In these types of indium-mediated additions, solvent plays a major role in determining the nature of the organoindium intermediate and we observed the susceptibility of some allylindium intermediates to hydrolysis in protic solvents. Under our reaction conditions using a polar aprotic solvent, we suggest that an allylindium(III) species is the active allylating intermediate. In addition, we have observed the presence of a shiny, indium(0) nugget throughout the reaction, irrespective of the stoichiometry, indicating disproportionation of indium halide byproduct formed during the reaction.

  8. Combining silver- and organocatalysis: an enantioselective sequential catalytic approach towards pyrano-annulated pyrazoles.

    Science.gov (United States)

    Hack, Daniel; Chauhan, Pankaj; Deckers, Kristina; Mizutani, Yusuke; Raabe, Gerhard; Enders, Dieter

    2015-02-11

    A one-pot asymmetric Michael addition/hydroalkoxylation sequence, catalyzed by a sequential catalytic system consisting of a squaramide and a silver salt, provides a new series of chiral pyrano-annulated pyrazole derivatives in excellent yields (up to 95%) and high enantioselectivities (up to 97% ee).

  9. Indium-mediated asymmetric Barbier-type propargylations: additions to aldehydes and ketones and mechanistic investigation of the organoindium reagents.

    Science.gov (United States)

    Haddad, Terra D; Hirayama, Lacie C; Buckley, Jannise J; Singaram, Bakthan

    2012-01-20

    We report a simple, efficient, and general method for the indium-mediated enantioselective propargylation of aromatic and aliphatic aldehydes under Barbier-type conditions in a one-pot synthesis affording the corresponding chiral alcohol products in very good yield (up to 90%) and enantiomeric excess (up to 95%). The extension of this methodology to ketones demonstrated the need for electrophilic ketones more reactive than acetophenone as the reaction would not proceed with just acetophenone. Using the Lewis acid indium triflate [In(OTf)(3)] induced regioselective formation of the corresponding homoallenic alcohol product from acetophenone. However, this methodology demonstrated excellent chemoselectivity in formation of only the corresponding secondary homopropargylic alcohol product in the presence of a ketone functionality. Investigation of the organoindium intermediates under our reaction conditions shows the formation of allenylindium species, and we suggest that these species contain an indium(III) center. In addition, we have observed the presence of a shiny, indium(0) nugget throughout the reaction, irrespective of the stoichiometry, indicating disproportionation of indium halide byproduct formed during the reaction.

  10. DNA-based asymmetric catalysis

    NARCIS (Netherlands)

    Boersma, Arnold J.; Megens, Rik P.; Feringa, Ben L.; Roelfes, Gerard

    2010-01-01

    The unique chiral structure of DNA has been a source of inspiration for the development of a new class of bio-inspired catalysts. The novel concept of DNA-based asymmetric catalysis, which was introduced only five years ago, has been applied successfully in a variety of catalytic enantioselective

  11. Catalytic diastereoselective tandem conjugate addition-elimination reaction of Morita-Baylis-Hillman C adducts by C-C bond cleavage

    KAUST Repository

    Yang, Wenguo

    2012-02-08

    Through the cleavage of the C-C bond, the first catalytic tandem conjugate addition-elimination reaction of Morita-Baylis-Hillman C adducts has been presented. Various S N2′-like C-, S-, and P-allylic compounds could be obtained with exclusive E configuration in good to excellent yields. The Michael product could also be easily prepared by tuning the β-C-substituent group of the α-methylene ester under the same reaction conditions. Calculated relative energies of various transition states by DFT methods strongly support the observed chemoselectivity and diastereoselectivity. © 2012 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim.

  12. Catalytic Asymmetric Synthesis of Both Enantiomers of 4‑Substituted 1,4-Dihydropyridines with the Use of Bifunctional Thiourea-Ammonium Salts Bearing Different Counterions

    Directory of Open Access Journals (Sweden)

    Kohzo Yoshida

    2010-11-01

    Full Text Available Organoammonium salts composed of a Brønsted acid and an anilinothiourea promoted the Michael addition of β-keto esters and α,β-unsaturated aldehydes in the presence of primary amines to give functionalized 1,4-dihydropyridines enantioselectively. With the use of the different Brønsted acids such as DFA and HBF4 with the same bifunctional thiourea, both enantiomers of 4-substituted 1,4-dihydropyridine were synthesized from the same starting materials.

  13. Effect of additives to VPO system on its catalytic properties in oxidative dehydrogenation of propane and ethane

    International Nuclear Information System (INIS)

    Gasior, M.; Gressel, I.; Grzybowska, B.; Zazhigalov, V.A.

    2003-01-01

    Oxidative dehydrogenation (ODH) of propane and ethane has been studied on VPO catalysts with additives of Bi, La, Mo, and Zr. The catalysts show promising properties in the ethane ODH, with selectiveness of ethene of ∼ 85% at 10% conversion of ethane, but are poor in the propane ODH (maximal selectivities to propene of ∼40%). For both alkanes introduction of the additives leads to an increase in the overall rate of the reaction. The effect of the additives on the selectivity to olefins is complex and depends on the reaction temperature, the additive content and the type of alkane. The same additive has in several cases an inverse effect on the selectivity for the propane and ethane ODH. The Mo additive and higher amounts of the La additive increase the selectivity to propane, whereas they decrease the selectivity of ethane. Low content of La additive gives rise of the increase of selectivity to ethane and decrease in that to propane. The differences between the selectivities to olefins in ODH of propane and ethane are discussed as being due to different acidic-basic properties of the propene and ethene and their different strength of bonding to the catalyst surface. (author)

  14. Catalytic Asymmetric Alkylation of Aryl Heteroaryl Ketones

    NARCIS (Netherlands)

    Ortiz, Pablo; Harutyunyan, Syuzanna; del Hoyo, Ana

    Tertiary diarylmethanols are highly bioactive structural motifs. A new strategy to access chiral tertiary diarylmethanols through copper-catalyzed direct alkylation of (di)(hetero)aryl ketones by using Grignard reagents was developed. The low reactivity and the similarity of the enantiotopic faces

  15. XPS-UPS, ISS characterization studies and the effect of Pt and K addition on the catalytic properties of MoO{sub 2-x}(OH){sub y} deposited on TiO{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Al-Kandari, H. [Public Authority of Applied Education and Training (Kuwait); Mohamed, A.M.; Al-Kharafi, F. [Kuwait University, Department of Chemistry, P.O. Box 5969, Safat 13060 (Kuwait); Katrib, A., E-mail: ali.katrib@ku.edu.kw [Kuwait University, Department of Chemistry, P.O. Box 5969, Safat 13060 (Kuwait)

    2011-11-15

    Highlights: {yields} Surface electronic structure-catalytic activity correlation is presented in this research work. {yields} In situ characterization by XPS-UPS and ISS techniques were employed at the same experimental conditions applied for catalytic reactions. {yields} Catalytic reactions of Mo deposited on titanium oxide for the isomerization and hydrogenation reactions using 1-hexene and n-hexane were studied. {yields} The bifunctional properties of the molybdenum dioxide phase were modified by the addition of potassium. - Abstract: Characterization by XPS-UPS, ISS surface techniques of MoO{sub 3}/TiO{sub 2} catalysts before and after addition of Pt (PtMo) 2.5% by weight of MoO{sub 3} and potassium (KMo) enabled to identify different chemical species present on the outermost surface layer at different reduction temperatures. Catalytic activities of these systems using 1-hexene and n-hexane reactants were studied. Correlation between catalytic activity and surface electronic structure enabled us to identify the chemical species, active site(s), responsible for specific catalytic reaction(s).

  16. XPS-UPS, ISS characterization studies and the effect of Pt and K addition on the catalytic properties of MoO2-x(OH)y deposited on TiO2

    International Nuclear Information System (INIS)

    Al-Kandari, H.; Mohamed, A.M.; Al-Kharafi, F.; Katrib, A.

    2011-01-01

    Highlights: → Surface electronic structure-catalytic activity correlation is presented in this research work. → In situ characterization by XPS-UPS and ISS techniques were employed at the same experimental conditions applied for catalytic reactions. → Catalytic reactions of Mo deposited on titanium oxide for the isomerization and hydrogenation reactions using 1-hexene and n-hexane were studied. → The bifunctional properties of the molybdenum dioxide phase were modified by the addition of potassium. - Abstract: Characterization by XPS-UPS, ISS surface techniques of MoO 3 /TiO 2 catalysts before and after addition of Pt (PtMo) 2.5% by weight of MoO 3 and potassium (KMo) enabled to identify different chemical species present on the outermost surface layer at different reduction temperatures. Catalytic activities of these systems using 1-hexene and n-hexane reactants were studied. Correlation between catalytic activity and surface electronic structure enabled us to identify the chemical species, active site(s), responsible for specific catalytic reaction(s).

  17. Baker's yeast catalyzed asymmetric reduction of methyl acetoacetate in glycerol containing systems

    Directory of Open Access Journals (Sweden)

    Adi Wolfson

    2008-09-01

    Full Text Available The asymmetric hydrogenation of methyl acetoacetate was successfully performed with baker's yeast in pure glycerol and mixtures of glycerol and water. Though yeast viability was very low after exposure to glycerol, the enzymatic activity in pure glycerol was preserved for some days. In addition, a mixture of glycerol and water combined the advantageous of each individual solvent and resulted in high catalytic performance and efficient product extraction yield

  18. An N-Linked Bidentate Phosphoramidite Ligand (N-Me-BIPAM for Rhodium-Catalyzed Asymmetric 1,4-Addition of Arylboronic Acids to α,β-Unsaturated Ketones

    Directory of Open Access Journals (Sweden)

    Norio Miyaura

    2012-12-01

    Full Text Available A new bidentate phosphoramidite (N-Me-BIPAM based on Shibasaki’s N-linked BINOL was synthesized. This ligand appears to be highly effective for rhodium-catalyzed asymmetric conjugated addition of arylboronic acids to α,β-unsaturated enones. The reaction of ortho-substituted arylboronic acid with acyclic and cyclic enones provides the corresponding products in good yields and enantioselectivities.

  19. Asymmetric Synthesis of γ-Lactones through Koga Amine-Controlled Addition of Enediolates to α,β-Unsaturated Sulfoxonium Salts.

    Science.gov (United States)

    Peraino, Nicholas J; Kaster, Sven H; Wheeler, Kraig A; Kerrigan, Nessan J

    2017-01-06

    A chiral Koga amine-controlled asymmetric synthesis of cis-γ-lactones through a formal [3 + 2] cycloaddition of enediolates with α,β-unsaturated sulfoxonium salts is described. The desired structural motif was formed in moderate to good yields (50-71% for 13 examples), with good to very good diastereoselectivity (dr 5:1 to 10:1 for 20 examples), favoring the cis-isomer, and good to excellent enantioselectivity (70-91% ee for 13 examples).

  20. A carbon nanotube confinement strategy to implement homogeneous asymmetric catalysis in the solid phase.

    Science.gov (United States)

    Hashimoto, Kazuki; Kumagai, Naoya; Shibasaki, Masakatsu

    2015-03-09

    A readily recyclable asymmetric catalyst has been developed based on the self-assembly of a homogeneous catalyst in a fibrous network of multiwalled carbon nanotubes (MWNTs). Dimerization of an amide-based chiral ligand with a suitable spacer allows for the efficient formation of a heterogeneous catalyst by self-assembly on addition of Er(OiPr)3. The self-assembly proceeds in the MWNT fibrous network and small clusters of assembled catalyst are confined in the MWNTs, producing an easily handled solid-phase catalyst. The resulting MWNT-confined catalyst exhibits a good catalytic performance in a catalytic asymmetric Mannich-type reaction, which can be conducted in a repeated batch system and in a continuous-flow platform. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Asymmetric catalysis in aqueous media: use of metal-chiral crown ethers as efficient chiral Lewis acid catalysts in asymmetric aldol reactions

    Directory of Open Access Journals (Sweden)

    Shu Kobayashi

    2001-01-01

    Full Text Available Metal-chiral crown ether complexes have been developed as efficient chiral Lewis acid catalysts for asymmetric aldol reactions of silyl enol ethers with aldehydes in aqueous media. While many excellent catalytic asymmetric reactions have been developed recently, most of them have to be carried out under strictly anhydrous conditions in organic solvents. This is probably due to the instability of many catalysts and/or intermediates in the presence of even a small amount of water. To address this issue, we searched for metal-crown ether complexes on the basis of our "multi-coordination" hypothesis, and found that lead(II and lanthanide(III catalysts worked well as chiral Lewis acids in aqueous media. To the best of our knowledge, these are the first examples of chiral crown-based Lewis acids that can be successfully used in catalytic asymmetric reactions. The catalysts have been characterized by X-ray diffraction, and their unique structures as chiral catalysts have been revealed. Use of water as a solvent is essential in these asymmetric catalysis, and the role of water on these reactions to explain the high reactivity and selectivity has been suggested. Another important point is that kinetic studies have shown the possibility that these types of crown ether complexes would be suitable as chiral catalysts employed in aqueous media. In addition, although the catalytic asymmetric aldol reactions are one of the most powerful carbon-carbon bond-forming methodologies and several successful examples have been reported, the use of aprotic anhydrous solvents and low reaction temperatures (-78 °C has been needed in almost all successful cases. On the other hand, the present reactions proceeded smoothly at -10-0 °C in water-alcohol solutions while retaining high levels of diastereo- and enantioselectivities.

  2. Palladium catalysed asymmetric alkylation of benzophenone Schiff ...

    Indian Academy of Sciences (India)

    Dongdaemun-Gu, Seoul 130-701, Republic of Korea. bDepartment of ..... Anionic effect of imidazolium based ionic liquids in catalytic asymmetric PT alkylationa promoted by palladium catalyst.b. Entry ... d: compared with the run involving catalyst only under similar PT conditions (entry 10, table 1) throw some light in this ...

  3. Magnetically Retrievable Catalysts for Asymmetric Synthesis

    Science.gov (United States)

    Surface modification of magnetic nanoparticles with chiral scaffolds for asymmetric catalytic applications is an elegant way of providing a special pseudo homogenous phase which could be separated using an external magnet. In this review, we summarize the use of magnetic nanopart...

  4. The catalystic asymmetric synthesis of optically active epoxy ketones

    NARCIS (Netherlands)

    Marsman, Bertha Gerda

    1981-01-01

    In this thesis the use of catalytic asymmetric synthesis to prepare optically active epoxy ketones is described. This means that the auxiliary chirality, necessary to obtain an optically active product, is added in a catalytic quantity . In principle this is a very efficient way to make opticlly

  5. Calcium(ii)-catalyzed enantioselective conjugate additions of amines.

    Science.gov (United States)

    Uno, Brice E; Dicken, Rachel D; Redfern, Louis R; Stern, Charlotte M; Krzywicki, Greg G; Scheidt, Karl A

    2018-02-14

    The direct enantioselective chiral calcium(ii)·phosphate complex (Ca[CPA] 2 )-catalyzed conjugate addition of unprotected alkyl amines to maleimides was developed. This mild catalytic system represents a significant advance towards the general convergent asymmetric amination of α,β-unsaturated electrophiles, providing medicinally relevant chiral aminosuccinimide products in high yields and enantioselectivities. Furthermore, the catalyst can be reused directly from a previously chromatographed reaction and still maintain both high yield and selectivity.

  6. Asymmetric Ashes

    Science.gov (United States)

    2006-11-01

    that oscillate in certain directions. Reflection or scattering of light favours certain orientations of the electric and magnetic fields over others. This is why polarising sunglasses can filter out the glint of sunlight reflected off a pond. When light scatters through the expanding debris of a supernova, it retains information about the orientation of the scattering layers. If the supernova is spherically symmetric, all orientations will be present equally and will average out, so there will be no net polarisation. If, however, the gas shell is not round, a slight net polarisation will be imprinted on the light. This is what broad-band polarimetry can accomplish. If additional spectral information is available ('spectro-polarimetry'), one can determine whether the asymmetry is in the continuum light or in some spectral lines. In the case of the Type Ia supernovae, the astronomers found that the continuum polarisation is very small so that the overall shape of the explosion is crudely spherical. But the much larger polarization in strongly blue-shifted spectral lines evidences the presence, in the outer regions, of fast moving clumps with peculiar chemical composition. "Our study reveals that explosions of Type Ia supernovae are really three-dimensional phenomena," says Dietrich Baade. "The outer regions of the blast cloud is asymmetric, with different materials found in 'clumps', while the inner regions are smooth." "This study was possible because polarimetry could unfold its full strength thanks to the light-collecting power of the Very Large Telescope and the very precise calibration of the FORS instrument," he adds. The research team first spotted this asymmetry in 2003, as part of the same observational campaign (ESO PR 23/03 and ESO PR Photo 26/05). The new, more extensive results show that the degree of polarisation and, hence, the asphericity, correlates with the intrinsic brightness of the explosion. The brighter the supernova, the smoother, or less clumpy

  7. Asymmetric Crater

    Science.gov (United States)

    2004-01-01

    [figure removed for brevity, see original site] Released 18 December 2003Asymmetric craters such as the one in the center of this image are fairly rare. The more typical symmetric craters are formed when meteors impact a surface over a wide range of angles. Only very low impact angles (within 15o of horizontal) result in asymmetric structures such as this one. The bilateral symmetry of the ejecta, like two wings on either side of the elliptical crater, is typical of oblique impacts. The small crater downrange from the main crater could have been caused by the impactor breaking apart before impact or possibly a 'decapitation' of the impactor as it hit with the 'head' traveling farther to form the smaller structure.Image information: VIS instrument. Latitude -8.5, Longitude 227.5 East (132.5 West). 19 meter/pixel resolution.Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  8. Asymmetric collider

    International Nuclear Information System (INIS)

    Bharadwaj, V.; Colestock, P.; Goderre, G.; Johnson, D.; Martin, P.; Holt, J.; Kaplan, D.

    1993-01-01

    The study of CP violation in beauty decay is one of the key challenges facing high energy physics. Much work has not yielded a definitive answer how this study might best be performed. However, one clear conclusion is that new accelerator facilities are needed. Proposals include experiments at asymmetric electron-positron colliders and in fixed-target and collider modes at LHC and SSC. Fixed-target and collider experiments at existing accelerators, while they might succeed in a first observation of the effect, will not be adequate to study it thoroughly. Giomataris has emphasized the potential of a new approach to the study of beauty CP violation: the asymmetric proton collider. Such a collider might be realized by the construction of a small storage ring intersecting an existing or soon-to-exist large synchrotron, or by arranging collisions between a large synchrotron and its injector. An experiment at such a collider can combine the advantages of fixed-target-like spectrometer geometry, facilitating triggering, particle identification and the instrumentation of a large acceptance, while the increased √s can provide a factor > 100 increase in beauty-production cross section compared to Tevatron or HERA fixed-target. Beams crossing at a non-zero angle can provide a small interaction region, permitting a first-level decay-vertex trigger to be implemented. To achieve large √s with a large Lorentz boost and high luminosity, the most favorable venue is the high-energy booster (HEB) at the SSC Laboratory, though the CERN SPS and Fermilab Tevatron are also worth considering

  9. Towards chiral diamines as chiral catalytic precursors for the borane ...

    Indian Academy of Sciences (India)

    2)-2-anilinomethylpiperidine (2) have been employed as chiral catalytic sources in the borane-mediated asymmetric reduction of prochiral ketones thus providing the resulting secondary alcohols in good enantiomeric purities (up to 81% ) ...

  10. Catalytic Conia-ene and related reactions.

    Science.gov (United States)

    Hack, Daniel; Blümel, Marcus; Chauhan, Pankaj; Philipps, Arne R; Enders, Dieter

    2015-10-07

    Since its initial inception, the Conia-ene reaction, known as the intramolecular addition of enols to alkynes or alkenes, has experienced a tremendous development and appealing catalytic protocols have emerged. This review fathoms the underlying mechanistic principles rationalizing how substrate design, substrate activation, and the nature of the catalyst work hand in hand for the efficient synthesis of carbocycles and heterocycles at mild reaction conditions. Nowadays, Conia-ene reactions can be found as part of tandem reactions, and the road for asymmetric versions has already been paved. Based on their broad applicability, Conia-ene reactions have turned into a highly appreciated synthetic tool with impressive examples in natural product synthesis reported in recent years.

  11. Highly Enantioselective Construction of Tertiary Thioethers and Alcohols via Phosphine-Catalyzed Asymmetric γ-Addition reactions of 5H-Thiazol-4-ones and 5H-Oxazol-4-ones: Scope and Mechanistic Understandings

    KAUST Repository

    Wang, Tianli

    2015-06-02

    Phosphine-catalyzed highly enantioselective γ-additions of 5H-thiazol-4-ones and 5H-oxazol-4-ones to allenoates have been developed for the first time. With the employment of amino-acid derived bifunctional phosphines, a wide range of substituted 5H-thiazol-4-one and 5H-oxazol-4-one derivatives bearing heteroarom (S or O)-containing tertiary chiral centers were constructed in high yields and excellent enantioselectivities. The reported method provides a facile access to enantioenriched tertiary thioether/alcohols. The mechanism of γ-addition reaction was investigated by performing DFT calculations, and the hydrogen bonding interactions between the Brønsted acid moiety of the phosphine catalysts and the “C=O” unit of donor molecules were shown to be crucial in asymmetric induction.

  12. How does the addition of steric hindrance to a typical N-heterocyclic carbene ligand affect catalytic activity in olefin metathesis?

    KAUST Repository

    Poater, Albert

    2013-01-01

    Density functional theory (DFT) calculations were used to predict and rationalize the effect of the modification of the structure of the prototype 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) N-heterocyclic carbene (NHC) ligand. The modification consists in the substitution of the methyl groups of ortho isopropyl substituent with phenyl groups, and here we plan to describe how such significant changes affect the metal environment and therefore the related catalytic behaviour. Bearing in mind that there is a significant structural difference between both ligands in different olefin metathesis reactions, here by means of DFT we characterize where the NHC ligand plays a more active role and where it is a simple spectator, or at least its modification does not significantly change its catalytic role/performance. © 2013 The Royal Society of Chemistry.

  13. Biomimetic asymmetric hydrogenation: in situ regenerable Hantzsch esters for asymmetric hydrogenation of benzoxazinones.

    Science.gov (United States)

    Chen, Qing-An; Chen, Mu-Wang; Yu, Chang-Bin; Shi, Lei; Wang, Duo-Sheng; Yang, Yan; Zhou, Yong-Gui

    2011-10-19

    A catalytic amount of Hantzsch ester that could be regenerated in situ by Ru complexes under hydrogen gas has been employed in the biomimetic asymmetric hydrogenation of benzoxazinones with up to 99% ee in the presence of chiral phosphoric acid. The use of hydrogen gas as a reductant for the regeneration of Hantzsch esters makes this hydrogenation an ideal atom economic process.

  14. Alkaline earth metal catalysts for asymmetric reactions.

    Science.gov (United States)

    Kobayashi, Shū; Yamashita, Yasuhiro

    2011-01-18

    The group 2 alkaline earth metals calcium (Ca), strontium (Sr), and barium (Ba) are among the most common elements on Earth, abundant in both the sea and the Earth's crust. Although they are familiar in our daily lives, their application to organic synthesis has, so far, been limited. Some particularly useful properties of these elements include (i) low electronegativity, (ii) a stable oxidation state of +2, meaning that they can potentially form two covalent bonds with anions, and (iii) the ability to occupy a variety of coordination sites due to their large ionic radius. Furthermore, the alkaline earth metals, found between the group 1 and group 3 elements, show mild but significant Lewis acidity, which can be harnessed to control coordinative molecules via a Lewis acid-base interaction. Taken together, these characteristics make the metals Ca, Sr, and Ba very promising components of highly functionalized acid-base catalysts. In this Account, we describe the development of chiral alkaline earth metal catalysts for asymmetric carbon-carbon bond-forming reactions. Recently prepared chiral alkaline earth metal complexes have shown high diastereo- and enantioselectivities in fundamental and important chemical transformations. We chose chiral bisoxazoline (Box) derivatives bearing a methylene tether as a ligand for chiral modification. These molecules are very useful because they can covalently coordinate to alkaline earth metals in a bidentate fashion through deprotonation of the tether portion. It was found that chiral calcium-Box complexes could successfully promote catalytic asymmetric 1,4-addition and [3 + 2] cycloaddition reactions with high diastereo- and enantioselectivities. Both the calcium-Box complexes and chiral strontium-bis-sulfonamide and chiral barium-BINOLate complexes could catalyze asymmetric 1,4-addition reactions with high enantioselectivities. Furthermore, we designed a calcium-neutral coordinative ligand complex as a new type of chiral alkaline

  15. Asymmetric synthesis of γ-chloro-α,β-diamino- and β,γ-aziridino-α-aminoacylpyrrolidines and -piperidines via stereoselective Mannich-type additions of N-(diphenylmethyleneglycinamides across α-chloro-N-sulfinylimines

    Directory of Open Access Journals (Sweden)

    Gert Callebaut

    2012-12-01

    Full Text Available The asymmetric synthesis of new chiral γ-chloro-α,β-diaminocarboxylamide derivatives by highly diastereoselective Mannich-type reactions of N-(diphenylmethyleneglycinamides across chiral α-chloro-N-p-toluenesulfinylaldimines was developed. The resulting (SS,2S,3S-γ-chloro-α,β-diaminocarboxylamides were formed with the opposite enantiotopic face selectivity as compared to the (SS,2R,3R-γ-chloro-α,β-diaminocarboxyl esters obtained via Mannich-type addition of analogous N-(diphenylmethyleneglycine esters across a chiral α-chloro-N-p-toluenesulfinylaldimine. Selective deprotection under different acidic reaction conditions and ring closure of the γ-chloro-α,β-diaminocarboxylamides was optimized, which resulted in Nα-deprotected syn-γ-chloro-α,β-diaminocarboxylamides, N-sulfinyl-β,γ-aziridino-α-aminocarboxylamide derivatives, a trans-imidazolidine, and an Nα,Nβ-deprotected syn-γ-chloro-α,β-diaminocarboxylamide.

  16. Asymmetric synthesis of α-amino acids via homologation of Ni(II) complexes of glycine Schiff bases. Part 2: aldol, Mannich addition reactions, deracemization and (S) to (R) interconversion of α-amino acids.

    Science.gov (United States)

    Sorochinsky, Alexander E; Aceña, José Luis; Moriwaki, Hiroki; Sato, Tatsunori; Soloshonok, Vadim

    2013-11-01

    This review provides a comprehensive treatment of literature data dealing with asymmetric synthesis of α-amino-β-hydroxy and α,β-diamino acids via homologation of chiral Ni(II) complexes of glycine Schiff bases using aldol and Mannich-type reactions. These reactions proceed with synthetically useful chemical yields and thermodynamically controlled stereoselectivity and allow direct introduction of two stereogenic centers in a single operation with predictable stereochemical outcome. Furthermore, new application of Ni(II) complexes of α-amino acids Schiff bases for deracemization of racemic α-amino acids and (S) to (R) interconversion providing additional synthetic opportunities for preparation of enantiomerically pure α-amino acids, is also reviewed. Origin of observed diastereo-/enantioselectivity in the aldol, Mannich-type and deracemization reactions, generality and limitations of these methodologies are critically discussed.

  17. Asymmetric Domino Aza-Michael Addition/[3+2] Cycloaddition Reactions as a Versatile Approach to alpha,beta,gamma,-Triamino Acid Derivatives

    Czech Academy of Sciences Publication Activity Database

    Kapras, Vojtěch; Pohl, Radek; Císařová, I.; Jahn, Ullrich

    2014-01-01

    Roč. 16, č. 4 (2014), s. 1088-1091 ISSN 1523-7060 Institutional support: RVO:61388963 Keywords : 1,3-dipolar cycloaddition * lithium amides * aza-Michael addition * amino acids * pyrazoles Subject RIV: CC - Organic Chemistry Impact factor: 6.364, year: 2014

  18. Synthesis of new pyrrolidine-based organocatalysts and study of their use in the asymmetric Michael addition of aldehydes to nitroolefins

    Directory of Open Access Journals (Sweden)

    Alejandro Castán

    2017-03-01

    Full Text Available New pyrrolidine-based organocatalysts with a bulky substituent at C2 were synthesized from chiral imines derived from (R-glyceraldehyde acetonide by diastereoselective allylation followed by a sequential hydrozirconation/iodination reaction. The new compounds were found to be effective organocatalysts for the Michael addition of aldehydes to nitroolefins and enantioselectivities up to 85% ee were achieved.

  19. Reversible tetramerization of human TK1 to the high catalytic efficient form is induced by pyrophosphate, in addition to tripolyphosphates, or high enzyme concentration

    DEFF Research Database (Denmark)

    Munch-Petersen, Birgitte

    2009-01-01

    of ATP is necessary for tetramerisation and how the reaction velocity is influenced by the enzyme concentration. The results show that only two or three of the phosphate groups of ATP are necessary for tetramerisation, and that kinetics and tetramerisation are closely related. Furthermore, enzyme...... concentration was found to have a pivotal effect on catalytic efficiency.......Thymidine kinase (TK1) is a key enzyme in the salvage pathway of deoxyribonucleotide metabolism catalyzing the first step in the synthesis of dTTP by the transfer of a gamma-phosphate group from a nucleoside triphosphate to the 5´-hydroxyl group of thymidine forming dTMP. Human TK1 is cytosolic...

  20. Protease-catalysed Direct Asymmetric Mannich Reaction in Organic Solvent

    Science.gov (United States)

    Xue, Yang; Li, Ling-Po; He, Yan-Hong; Guan, Zhi

    2012-10-01

    We reported the first enzyme-catalysed, direct, three-component asymmetric Mannich reaction using protease type XIV from Streptomyces griseus (SGP) in acetonitrile. Yields of up to 92% with enantioselectivities of up to 88% e.e. and diastereoselectivities of up to 92:8 (syn:anti) were achieved under the optimised conditions. This enzyme's catalytic promiscuity expands the application of this biocatalyst and provides a potential alternative method for asymmetric Mannich reactions.

  1. Catalytic bioreactors and methods of using same

    Science.gov (United States)

    Worden, Robert Mark; Liu, Yangmu Chloe

    2017-07-25

    Various embodiments provide a bioreactor for producing a bioproduct comprising one or more catalytically active zones located in a housing and adapted to keep two incompatible gaseous reactants separated when in a gas phase, wherein each of the one or more catalytically active zones may comprise a catalytic component retainer and a catalytic component retained within and/or thereon. Each of the catalytically active zones may additionally or alternatively comprise a liquid medium located on either side of the catalytic component retainer. Catalytic component may include a microbial cell culture located within and/or on the catalytic component retainer, a suspended catalytic component suspended in the liquid medium, or a combination thereof. Methods of using various embodiments of the bioreactor to produce a bioproduct, such as isobutanol, are also provided.

  2. The Impact of Ce-Zr Addition on Nickel Dispersion and Catalytic Behavior for CO2 Methanation of Ni/AC Catalyst at Low Temperature

    Directory of Open Access Journals (Sweden)

    Minh Cam Le

    2017-01-01

    Full Text Available The CO2 methanation was studied over 7 wt.% nickel supported on Ce0.2Zr0.8O2/AC to evaluate the correlation of the structural properties with catalytic performance. The catalysts were investigated in more detail by means of X-ray diffraction (XRD, transmission electron microscopy (TEM, and scanning electron microscopy (SEM. A sample of 7 wt.% nickel loading supported on activated carbon (AC was also prepared for comparison. The results demonstrated that the ceria-zirconia solid solution phase could disperse and stabilize the nickel species more effectively and resulted in stronger interaction with nickel than the parent activated carbon phase. Therefore, 7% Ni/Ce0.2Zr0.8O2/AC catalyst exhibited higher activity for CO2 reduction than 7% Ni//AC. It can attain 85% CO2 conversion at 350°C and have a CH4 selectivity of 100% at a pressure as low as 1 atm. The high activity of prepared catalysts is attributed to the good interaction between Ni and Ce0.2Zr0.8O2 and the high CO2 adsorption capacity of the activated carbon as well.

  3. Catalytic devices

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Ming; Zhang, Xiang

    2018-01-23

    This disclosure provides systems, methods, and apparatus related to catalytic devices. In one aspect, a device includes a substrate, an electrically insulating layer disposed on the substrate, a layer of material disposed on the electrically insulating layer, and a catalyst disposed on the layer of material. The substrate comprises an electrically conductive material. The substrate and the layer of material are electrically coupled to one another and configured to have a voltage applied across them.

  4. Asymmetric photoredox transition-metal catalysis activated by visible light

    Science.gov (United States)

    Huo, Haohua; Shen, Xiaodong; Wang, Chuanyong; Zhang, Lilu; Röse, Philipp; Chen, Liang-An; Harms, Klaus; Marsch, Michael; Hilt, Gerhard; Meggers, Eric

    2014-11-01

    Asymmetric catalysis is seen as one of the most economical strategies to satisfy the growing demand for enantiomerically pure small molecules in the fine chemical and pharmaceutical industries. And visible light has been recognized as an environmentally friendly and sustainable form of energy for triggering chemical transformations and catalytic chemical processes. For these reasons, visible-light-driven catalytic asymmetric chemistry is a subject of enormous current interest. Photoredox catalysis provides the opportunity to generate highly reactive radical ion intermediates with often unusual or unconventional reactivities under surprisingly mild reaction conditions. In such systems, photoactivated sensitizers initiate a single electron transfer from (or to) a closed-shell organic molecule to produce radical cations or radical anions whose reactivities are then exploited for interesting or unusual chemical transformations. However, the high reactivity of photoexcited substrates, intermediate radical ions or radicals, and the low activation barriers for follow-up reactions provide significant hurdles for the development of efficient catalytic photochemical processes that work under stereochemical control and provide chiral molecules in an asymmetric fashion. Here we report a highly efficient asymmetric catalyst that uses visible light for the necessary molecular activation, thereby combining asymmetric catalysis and photocatalysis. We show that a chiral iridium complex can serve as a sensitizer for photoredox catalysis and at the same time provide very effective asymmetric induction for the enantioselective alkylation of 2-acyl imidazoles. This new asymmetric photoredox catalyst, in which the metal centre simultaneously serves as the exclusive source of chirality, the catalytically active Lewis acid centre, and the photoredox centre, offers new opportunities for the `green' synthesis of non-racemic chiral molecules.

  5. Metal-catalyzed Asymmetric Hetero-Diels-Alder Reactions of Unactivated Dienes with Glyoxylates

    DEFF Research Database (Denmark)

    Johannsen, Mogens; Yao, Sulan; Graven, Anette

    1998-01-01

    The development of a catalytic asymmetric hetero-Diels-Alder methodology for the reaction of unactivated dienes with glyoxylates is presented. Several different asymmetric catalysts can be used, but copper-bisoxazolines and aluminium-BINOL give the highest yield, and the best chemo- and enantiose...

  6. Direct catalytic enantio- and diastereoselective Mannich reaction of isocyanoacetates and ketimines.

    Science.gov (United States)

    Ortín, Irene; Dixon, Darren J

    2014-03-24

    A catalytic asymmetric synthesis of imidazolines with a fully substituted β-carbon atom by a Mannich-type addition/cyclization reaction of isocyanoacetate pronucleophiles and N-diphenylphosphinoyl ketimines has been developed. When a combination of a cinchona-derived aminophosphine precatalyst and silver oxide was employed as a binary catalyst system, good reactivity, high diastereoselectivities (up to 99:1 d.r.), and excellent enantioselectivities (up to 99% ee) were obtained for a range of substrates. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Asymmetric bipolar membrane: A tool to improve product purity

    NARCIS (Netherlands)

    Balster, J.H.; Sumbharaju, R.; Srikantharajah, S.; Punt, Ineke G.M.; Stamatialis, Dimitrios; Jordan, V.; Wessling, Matthias

    2007-01-01

    Bipolar membranes (BPMs) are catalytic membranes for electro-membrane processes splitting water into protons and hydroxyl ions. To improve selectivity and current efficiency of BPMs, we prepare new asymmetric BPMs with reduced salt leakages. The flux of salt ions across a BPM is determined by the

  8. The effect of additives on the reactivity of palladium surfaces for the chemisorption and hydrogenation of carbon monoxide: A surface science and catalytic study. [LaMO/sub 3/(M = Cr, Mn, Fe, Co, Rh)

    Energy Technology Data Exchange (ETDEWEB)

    Rucker, T.G.

    1987-06-01

    This research studied the role of surface additives on the catalytic activity and chemisorptive properties of Pd single crystals and foils. Effects of Na, K, Si, P, S, and Cl on the bonding of CO and H and on the cyclotrimerization of acetylene on the (111), (100) and (110) faces of Pd were investigated in addition to role of TiO/sub 2/ and SiO/sub 2/ overlayers deposited on Pd foils in the CO hydrogenation reaction. On Pd, only in the presence of oxide overlayers, are methane or methanol formed from CO and H/sub 2/. The maximum rate of methane formation is attained on Pd foil where 30% of the surface is covered with titania. Methanol formation can be achieved only if the TiO/sub x//Pd surface is pretreated in 50 psi of oxygen at 550/sup 0/C prior to the reaction. The additives (Na, K, Si, P, S, Cl) affect the bonding of CO and hydrogen and the cyclotrimerization of acetylene to benzene by structural and electronic interactions. In general, the electron donating additives increase the desorption temperature of CO and increase the rate of acetylene cyclotrimerization and the electron withdrawing additives decrease the desorption temperature of CO and decrease the rate of benzene formation from acetylene.

  9. The Long Isoform of Terminal Deoxynucleotidyl Transferase Enters the Nucleus And, Rather than Catalyzing Nontemplated Nucleotide Addition, Modulates the Catalytic Activity of the Short Isoform

    OpenAIRE

    Benedict, Cindy L.; Gilfillan, Susan; Kearney, John F.

    2001-01-01

    During variable/diversity/joining (V[D]J) recombination, the enzyme terminal deoxynucleotidyl transferase (Tdt) adds random nucleotides at the junctions of the rearranging gene segments, increasing diversity of the antibody (Ab) and T cell receptor repertoires. Two splice variants of Tdt have been described, but only one (short isoform of Tdt [TdtS]) has been convincingly demonstrated to catalyze nontemplated (N) addition in vitro. We have expressed each splice variant of Tdt in transgenic (T...

  10. Organocatalyzed Asymmetric Synthesis of Axially, Planar, and Helical Chiral Compounds.

    Science.gov (United States)

    Shirakawa, Seiji; Liu, Shiyao; Kaneko, Shiho

    2016-02-04

    Axially, planar, and helical chiral compounds are indispensable building blocks in modern organic synthesis. A wide variety of chiral ligands and catalysts were designed based on these chiral scaffolds, and these chiral ligands and catalysts were used for various catalytic asymmetric transformations to produce important chiral compounds in an optically enriched form. Furthermore, these chiral skeletons are found in the structure of biologically active natural products. Thus, the development of efficient enantioselective methods for the synthesis of these chiral compounds is an important task in the field of organic chemistry. In the last few years, organocatalyzed approaches, which are one of the most reliable catalytic asymmetric methods, became a hot topic. This Focus Review summarizes asymmetric organocatalytic methods for the synthesis of axially, planar, and helical chiral compounds as useful chiral building blocks. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. EXPERIMENTAL EVIDENCE FOR THE FORMATION OF HIGHLY SUPERHYDROGENATED POLYCYCLIC AROMATIC HYDROCARBONS THROUGH H ATOM ADDITION AND THEIR CATALYTIC ROLE IN H2 FORMATION

    DEFF Research Database (Denmark)

    Thrower, John; Jørgensen, Bjarke; Friis, Emil Enderup

    2012-01-01

    Mass spectrometry measurements show the formation of highly superhydrogenated derivatives of the polycyclic aromatic hydrocarbon molecule coronene through H atom addition reactions. The observed product mass distribution provides evidence also for abstraction reactions resulting in H2 formation......, in agreement with recent IR measurements. Complementary density functional theory calculations confirm the stability of the observed superhydrogenated species toward spontaneous H and H2 loss indicating that abstraction reactions may be the dominant route to H2 formation involving neutral polycyclic aromatic...... hydrocarbons (PAHs). The results indicate that highly superhydrogenated PAHs could well be formed and could act as efficient catalysts for H2 formation in the interstellar medium in low UV flux regions....

  12. Asymmetric Synthesis of Apratoxin E.

    Science.gov (United States)

    Mao, Zhuo-Ya; Si, Chang-Mei; Liu, Yi-Wen; Dong, Han-Qing; Wei, Bang-Guo; Lin, Guo-Qiang

    2016-10-21

    An efficient method for asymmetric synthesis of apratoxin E 2 is described in this report. The chiral lactone 8, recycled from the degradation of saponin glycosides, was utilized to prepare the non-peptide fragment 6. In addition to this "from nature to nature" strategy, olefin cross-metathesis (CM) was applied as an alternative approach for the formation of the double bond. Moreover, pentafluorophenyl diphenylphosphinate was found to be an efficient condensation reagent for the macrocyclization.

  13. Chiral Brønsted Acids for Asymmetric Organocatalysis

    Science.gov (United States)

    Kampen, Daniela; Reisinger, Corinna M.; List, Benjamin

    Chiral Brønsted acid catalysis is an emerging area of organocatalysis. Since the pioneering studies of the groups of Akiyama and Terada in 2004 on the use of chiral BINOL phosphates as powerful Brønsted acid catalysts in asymmetric Mannich-type reactions, numerous catalytic asymmetric transformations involving imine activation have been realized by means of this catalyst class, including among others Friedel-Crafts, Pictet-Spengler, Strecker, cycloaddition reactions, transfer hydrogenations, and reductive aminations. More recently, chiral BINOL phosphates found application in multicomponent and cascade reactions as for example in an asymmetric version of the Biginelli reaction. With the introduction of chiral BINOL-derived N-triflyl phosphoramides in 2006, asymmetric Brønsted acid catalysis is no longer restricted to reactive substrates. Also certain carbonyl compounds can be activated through these stronger Brønsted acid catalysts. In dealing with sensitive substrate classes, chiral dicarboxylic acids proved of particular value.

  14. Catalytic Enantioselective Synthesis of Naturally Occurring Butenolides via Hetero-Allylic Alkylation and Ring Closing Metathesis

    NARCIS (Netherlands)

    Mao, Bin; Geurts, Koen; Fañanás-Mastral, Martín; Zijl, Anthoni W. van; Fletcher, Stephen P.; Minnaard, Adriaan J.; Feringa, Bernard

    2011-01-01

    An efficient catalytic asymmetric synthesis of chiral γ-butenolides was developed based on the hetero-allylic asymmetric alkylation (h-AAA) in combination with ring closing metathesis (RCM). The synthetic potential of the h-AAA-RCM protocol was illustrated with the facile synthesis of (-)-whiskey

  15. Catalytic enantioselective synthesis of naturally occurring butenolides via hetero-allylic alkylation and ring closing metathesis.

    Science.gov (United States)

    Mao, Bin; Geurts, Koen; Fañanás-Mastral, Martín; van Zijl, Anthoni W; Fletcher, Stephen P; Minnaard, Adriaan J; Feringa, Ben L

    2011-03-04

    An efficient catalytic asymmetric synthesis of chiral γ-butenolides was developed based on the hetero-allylic asymmetric alkylation (h-AAA) in combination with ring closing metathesis (RCM). The synthetic potential of the h-AAA-RCM protocol was illustrated with the facile synthesis of (-)-whiskey lactone, (-)-cognac lactone, (-)-nephrosteranic acid, and (-)-roccellaric acid.

  16. Asymmetric Cache Coherency: Policy Modifications to Improve Multicore Performance

    OpenAIRE

    Shield, John; Diguet, Jean-Philippe; Gogniat, Guy

    2012-01-01

    International audience; Asymmetric coherency is a new optimisation method for coherency policies to support non-uniform work- loads in multicore processors. Asymmetric coherency assists in load balancing a workload and this is applica- ble to SoC multicores where the applications are not evenly spread among the processors and customization of the coherency is possible. Asymmetric coherency is a policy change, and consequently our designs re- quire little or no additional hardware over an exis...

  17. Towards chiral diamines as chiral catalytic precursors for the borane ...

    Indian Academy of Sciences (India)

    Administrator

    anilinomethylpiperidine (2) have been employed as chiral catalytic sources in the borane-mediated asymmetric reduction of prochiral ketones ..... 7⋅86 min (S) and 8.53 min (R)]. 2.7c (S)-2-Bromo-1-(4-bromophenyl)ethanol [(S)– ... of (a) compound 8 and (b) compound 15-TFA salt (Hydrogen atoms were omitted for clarity).

  18. Direct synthesis of cis-dihalido-bis(NHC) complex of nickel(II) and catalytic application in olefin addition polymerization: effect of halogen co-ligands and density functional theory study.

    Science.gov (United States)

    Zhang, Dao; Zhou, Sen; Li, Zhiming; Wang, Quanrui; Weng, Linhong

    2013-09-07

    Two novel amine-containing N-heterocyclic carbene ligand precursors [H(1a-b)]Br have been prepared in good yield and fully characterized. Direct syntheses of cis- and trans-dihalido-bis(NHC) nickel complexes [Ni(NHC)2X2] (X = Cl, Br) are reported. The solid structures of trans-[Ni(1a-b)2Br2] (2a-b) and cis-[Ni(1a)2Cl2] (3) were determined by single-crystal X-ray analysis and 3 was found to be the first example of cis-configuration coordination of monodentate NHC ligands to a metal center for dihalido-bis(NHC) nickel complexes. DFT calculations were conducted to determine the energy difference between cis- and trans-isomers of complexes 2a and 3 bearing bromide and chloride co-ligands. The cis-[Ni(1a)2Cl2] (cis-3) is 1.77-1.55 kcal mol(-1) lower in energy than its trans-isomer in polar solvents including CH2Cl2 and THF, while the trans-[Ni(1a)2Br2] (trans-2a) is more stable than the cis-isomer similarly in the gas phase. The cis nickel complex 3 with two coordinated monodentate NHCs was tested for olefin addition polymerization at standard conditions. It was found that cis-3 was inactive in ethylene polymerization but showed moderate catalytic activities (0.5-3.0 × 10(6) g of PNB (mol of Ni)(-1) h(-1)) in the addition polymerization of norbornene in the presence of methylaluminoxane (MAO) as cocatalyst.

  19. Asymmetrical field emitter

    Science.gov (United States)

    Fleming, J.G.; Smith, B.K.

    1995-10-10

    A method is disclosed for providing a field emitter with an asymmetrical emitter structure having a very sharp tip in close proximity to its gate. One preferred embodiment of the present invention includes an asymmetrical emitter and a gate. The emitter having a tip and a side is coupled to a substrate. The gate is connected to a step in the substrate. The step has a top surface and a side wall that is substantially parallel to the side of the emitter. The tip of the emitter is in close proximity to the gate. The emitter is at an emitter potential, and the gate is at a gate potential such that with the two potentials at appropriate values, electrons are emitted from the emitter. In one embodiment, the gate is separated from the emitter by an oxide layer, and the emitter is etched anisotropically to form its tip and its asymmetrical structure. 17 figs.

  20. LG tools for asymmetric wargaming

    Science.gov (United States)

    Stilman, Boris; Yakhnis, Alex; Yakhnis, Vladimir

    2002-07-01

    Asymmetric operations represent conflict where one of the sides would apply military power to influence the political and civil environment, to facilitate diplomacy, and to interrupt specified illegal activities. This is a special type of conflict where the participants do not initiate full-scale war. Instead, the sides may be engaged in a limited open conflict or one or several sides may covertly engage another side using unconventional or less conventional methods of engagement. They may include peace operations, combating terrorism, counterdrug operations, arms control, support of insurgencies or counterinsurgencies, show of force. An asymmetric conflict can be represented as several concurrent interlinked games of various kinds: military, transportation, economic, political, etc. Thus, various actions of peace violators, terrorists, drug traffickers, etc., can be expressed via moves in different interlinked games. LG tools allow us to fully capture the specificity of asymmetric conflicts employing the major LG concept of hypergame. Hypergame allows modeling concurrent interlinked processes taking place in geographically remote locations at different levels of resolution and time scale. For example, it allows us to model an antiterrorist operation taking place simultaneously in a number of countries around the globe and involving wide range of entities from individuals to combat units to governments. Additionally, LG allows us to model all sides of the conflict at their level of sophistication. Intelligent stakeholders are represented by means of LG generated intelligent strategies. TO generate those strategies, in addition to its own mathematical intelligence, the LG algorithm may incorporate the intelligence of the top-level experts in the respective problem domains. LG models the individual differences between intelligent stakeholders. The LG tools make it possible to incorporate most of the known traits of a stakeholder, i.e., real personalities involved in

  1. Renaissance of pyridine-oxazolines as chiral ligands for asymmetric catalysis.

    Science.gov (United States)

    Yang, Guoqiang; Zhang, Wanbin

    2018-03-05

    Oxazoline-containing ligands have been widely employed in numerous asymmetric catalytic reactions. Pyridine-oxazoline-type ligands, a class of hybrid ligands, were designed earlier than bisoxazoline and phosphine-oxazoline ligands; however, their unique properties have only been discovered recently. Pyridine-oxazoline-type chiral ligands are rapidly becoming popular for use in asymmetric catalysis, especially for several new and efficient asymmetric methodologies. Several types of challenging asymmetric reactions have been discovered recently using pyridine-oxazoline-type ligands showing their special properties and potential for future application in a wide range of new catalytic methodologies. This review provides an overview of this field, with the aim of highlighting both ligand design and synthetic methodology development.

  2. Asymmetric reactions in continuous flow

    Directory of Open Access Journals (Sweden)

    Xiao Yin Mak

    2009-04-01

    Full Text Available An overview of asymmetric synthesis in continuous flow and microreactors is presented in this review. Applications of homogeneous and heterogeneous asymmetric catalysis as well as biocatalysis in flow are discussed.

  3. A combined continuous microflow photochemistry and asymmetric organocatalysis approach for the enantioselective synthesis of tetrahydroquinolines

    Directory of Open Access Journals (Sweden)

    Erli Sugiono

    2013-11-01

    Full Text Available A continuous-flow asymmetric organocatalytic photocyclization–transfer hydrogenation cascade reaction has been developed. The new protocol allows the synthesis of tetrahydroquinolines from readily available 2-aminochalcones using a combination of photochemistry and asymmetric Brønsted acid catalysis. The photocylization and subsequent reduction was performed with catalytic amount of chiral BINOL derived phosphoric acid diester and Hantzsch dihydropyridine as hydrogen source providing the desired products in good yields and with excellent enantioselectivities.

  4. How Is Nature Asymmetric?

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 7; Issue 6. How Is Nature Asymmetric? - Discrete Symmetries in Particle Physics and their Violation ... Indian Institute of Technology, Chennai. Aligarh Muslim University. University of Rajasthan, Jaipur. Indian Institute of Science, Bangalore 560012, India.

  5. Chiral phase-transfer catalysis in the asymmetric α-heterofunctionalization of prochiral nucleophiles

    Directory of Open Access Journals (Sweden)

    Johannes Schörgenhumer

    2017-08-01

    Full Text Available Chiral phase-transfer catalysis is one of the major catalytic principles in asymmetric catalysis. A broad variety of different catalysts and their use for challenging applications have been reported over the last decades. Besides asymmetric C–C bond forming reactions the use of chiral phase-transfer catalysts for enantioselective α-heterofunctionalization reactions of prochiral nucleophiles became one of the most important field of application of this catalytic principle. Based on several highly spectacular recent reports, we thus wish to discuss some of the most important achievements in this field within the context of this review.

  6. Novel Catalytic Membrane Reactors

    Energy Technology Data Exchange (ETDEWEB)

    Stuart Nemser, PhD

    2010-10-01

    There are many industrial catalytic organic reversible reactions with amines or alcohols that have water as one of the products. Many of these reactions are homogeneously catalyzed. In all cases removal of water facilitates the reaction and produces more of the desired chemical product. By shifting the reaction to right we produce more chemical product with little or no additional capital investment. Many of these reactions can also relate to bioprocesses. Given the large number of water-organic compound separations achievable and the ability of the Compact Membrane Systems, Inc. (CMS) perfluoro membranes to withstand these harsh operating conditions, this is an ideal demonstration system for the water-of-reaction removal using a membrane reactor. Enhanced reaction synthesis is consistent with the DOE objective to lower the energy intensity of U.S. industry 25% by 2017 in accord with the Energy Policy Act of 2005 and to improve the United States manufacturing competitiveness. The objective of this program is to develop the platform technology for enhancing homogeneous catalytic chemical syntheses.

  7. Asymmetric silver-catalysed intermolecular bromotrifluoromethoxylation of alkenes with a new trifluoromethoxylation reagent

    Science.gov (United States)

    Guo, Shuo; Cong, Fei; Guo, Rui; Wang, Liang; Tang, Pingping

    2017-06-01

    Fluorinated organic compounds are becoming increasingly important in pharmaceuticals, agrochemicals and materials science. The introduction of trifluoromethoxy groups into new drugs and agrochemicals has attracted much attention due to their strongly electron-withdrawing nature and high lipophilicity. However, synthesis of trifluoromethoxylated organic molecules is difficult owing to the decomposition of trifluoromethoxide anion and β-fluoride elimination from transition-metal-trifluoromethoxide complexes, and no catalytic enantioselective trifluoromethoxylation reaction has been reported until now. Here, we present an example of an asymmetric silver-catalysed intermolecular bromotrifluoromethoxylation of alkenes with trifluoromethyl arylsulfonate (TFMS) as a new trifluoromethoxylation reagent. Compared to other trifluoromethoxylation reagents, TFMS is easily prepared and thermally stable with good reactivity. In addition, this reaction is operationally simple, scalable and proceeds under mild reaction conditions. Furthermore, broad scope and good functional group compatibility has been demonstrated by application of the method to the bromotrifluoromethoxylation of double bonds in natural products and natural product derivatives.

  8. Palladium catalysed asymmetric alkylation of benzophenone Schiff ...

    Indian Academy of Sciences (India)

    Asymmetric alkyl substitution of various benzophenone Schiff base substrates under biphasic conditions proceeded using optically active Palladium(II) complexes. The corresponding products were obtained in high yields but with moderate enantiomeric excess (ee). Addition of specific ionic liquids to the reaction medium ...

  9. Direct Asymmetric Vinylogous and Bisvinylogous Mannich-Type Reaction Catalyzed by a Copper(I) Complex.

    Science.gov (United States)

    Zhang, Hai-Jun; Shi, Chang-Yun; Zhong, Feng; Yin, Liang

    2017-02-15

    A direct catalytic asymmetric vinylogous Mannich-type reaction has been disclosed in good yield, excellent regio-, diastereo- and enantioselectivity. The key to control the regioselectivity is the combination of a bulky N-acylpyrazole and a bulky bisphosphine ligand. The catalytic system was extended to a bisvinylogous Mannich-type reaction by changing the ligand. The synthetic utility of the vinylogous products was demonstrated by several transformations.

  10. Diesel engine catalytic combustor system. [aircraft engines

    Science.gov (United States)

    Ream, L. W. (Inventor)

    1984-01-01

    A low compression turbocharged diesel engine is provided in which the turbocharger can be operated independently of the engine to power auxiliary equipment. Fuel and air are burned in a catalytic combustor to drive the turbine wheel of turbine section which is initially caused to rotate by starter motor. By opening a flapper value, compressed air from the blower section is directed to catalytic combustor when it is heated and expanded, serving to drive the turbine wheel and also to heat the catalytic element. To start, engine valve is closed, combustion is terminated in catalytic combustor, and the valve is then opened to utilize air from the blower for the air driven motor. When the engine starts, the constituents in its exhaust gas react in the catalytic element and the heat generated provides additional energy for the turbine section.

  11. Multipartite asymmetric quantum cloning

    International Nuclear Information System (INIS)

    Iblisdir, S.; Gisin, N.; Acin, A.; Cerf, N.J.; Filip, R.; Fiurasek, J.

    2005-01-01

    We investigate the optimal distribution of quantum information over multipartite systems in asymmetric settings. We introduce cloning transformations that take N identical replicas of a pure state in any dimension as input and yield a collection of clones with nonidentical fidelities. As an example, if the clones are partitioned into a set of M A clones with fidelity F A and another set of M B clones with fidelity F B , the trade-off between these fidelities is analyzed, and particular cases of optimal N→M A +M B cloning machines are exhibited. We also present an optimal 1→1+1+1 cloning machine, which is an example of a tripartite fully asymmetric cloner. Finally, it is shown how these cloning machines can be optically realized

  12. Ruthenium complexes with chiral tetradentate PNNP ligands: asymmetric catalysis from the viewpoint of inorganic chemistry.

    Science.gov (United States)

    Mezzetti, Antonio

    2010-09-14

    This is a personal account of the application of ruthenium complexes containing chiral tetradentate ligands with a P(2)N(2) ligand set (PNNP) as catalyst precursors for enantioselective "atom transfer" reactions. Therewith are meant reactions that involve bond formation between a metal-coordinated molecule and a free reagent. The reactive fragment (e.g. carbene) is transferred either from the metal to the non-coordinated substrate (e.g. olefin) or from the free reagent (e.g. F(+)) to the metal-bound substrate (e.g.beta-ketoester), depending on the class of catalyst (monocationic, Class A; or dicationic, Class B). The monocationic five-coordinate species [RuCl(PNNP)](+) and the six-coordinate complexes [RuCl(L)(PNNP)](+) (L = Et(2)O, H(2)O) of Class A catalyse asymmetric epoxidation, cyclopropanation (carbene transfer from the metal to the free olefin), and imine aziridination. Alternatively, the dicationic complexes [Ru(L-L)(PNNP)](2+) (Class B), which contain substrates that act as neutral bidentate ligands L-L (e.g., beta-ketoesters), catalyse Michael addition, electrophilic fluorination, and hydroxylation reactions. Additionally, unsaturated beta-ketoesters form dicationic complexes of Class B that catalyse Diels-Alder reactions with acyclic dienes to produce tetrahydro-1-indanones and estrone derivatives. Excellent enantioselectivity has been achieved in several of the catalytic reactions mentioned above. The study of key reaction intermediates (both in the solid state and in solution) has revealed significant mechanistic aspects of the catalytic reactions.

  13. Asymmetric Evolutionary Games.

    Science.gov (United States)

    McAvoy, Alex; Hauert, Christoph

    2015-08-01

    Evolutionary game theory is a powerful framework for studying evolution in populations of interacting individuals. A common assumption in evolutionary game theory is that interactions are symmetric, which means that the players are distinguished by only their strategies. In nature, however, the microscopic interactions between players are nearly always asymmetric due to environmental effects, differing baseline characteristics, and other possible sources of heterogeneity. To model these phenomena, we introduce into evolutionary game theory two broad classes of asymmetric interactions: ecological and genotypic. Ecological asymmetry results from variation in the environments of the players, while genotypic asymmetry is a consequence of the players having differing baseline genotypes. We develop a theory of these forms of asymmetry for games in structured populations and use the classical social dilemmas, the Prisoner's Dilemma and the Snowdrift Game, for illustrations. Interestingly, asymmetric games reveal essential differences between models of genetic evolution based on reproduction and models of cultural evolution based on imitation that are not apparent in symmetric games.

  14. Asymmetric Evolutionary Games.

    Directory of Open Access Journals (Sweden)

    Alex McAvoy

    2015-08-01

    Full Text Available Evolutionary game theory is a powerful framework for studying evolution in populations of interacting individuals. A common assumption in evolutionary game theory is that interactions are symmetric, which means that the players are distinguished by only their strategies. In nature, however, the microscopic interactions between players are nearly always asymmetric due to environmental effects, differing baseline characteristics, and other possible sources of heterogeneity. To model these phenomena, we introduce into evolutionary game theory two broad classes of asymmetric interactions: ecological and genotypic. Ecological asymmetry results from variation in the environments of the players, while genotypic asymmetry is a consequence of the players having differing baseline genotypes. We develop a theory of these forms of asymmetry for games in structured populations and use the classical social dilemmas, the Prisoner's Dilemma and the Snowdrift Game, for illustrations. Interestingly, asymmetric games reveal essential differences between models of genetic evolution based on reproduction and models of cultural evolution based on imitation that are not apparent in symmetric games.

  15. Contributions to the theory of catalytic titrations-III Neutralization catalytic titrations.

    Science.gov (United States)

    Gaál, F F; Abramović, B F

    1985-07-01

    Neutralization catalytic titrations of weak monoprotic adds and bases with both volumetric and coulometric addition of the titrant (strong base/acid) have been simulated by taking into account the equilibrium concentration of the catalyst during the titration. The influence of several factors on the shape of the simulated catalytic titration curve has been investigated and is discussed.

  16. Structure of the catalytic chain of Methanococcus jannaschii aspartate transcarbamoylase in a hexagonal crystal form: insights into the path of carbamoyl phosphate to the active site of the enzyme.

    Science.gov (United States)

    Vitali, Jacqueline; Singh, Aditya K; Soares, Alexei S; Colaneri, Michael J

    2012-05-01

    Crystals of the catalytic chain of Methanococcus jannaschii aspartate transcarbamoylase (ATCase) grew in the presence of the regulatory chain in the hexagonal space group P6(3)22, with one monomer per asymmetric unit. This is the first time that crystals with only one monomer in the asymmetric unit have been obtained; all known structures of the catalytic subunit contain several crystallographically independent monomers. The symmetry-related chains form the staggered dimer of trimers observed in the other known structures of the catalytic subunit. The central channel of the catalytic subunit contains a sulfate ion and a K(+) ion as well as a glycerol molecule at its entrance. It is possible that it is involved in channeling carbamoyl phosphate (CP) to the active site of the enzyme. A second sulfate ion near Arg164 is near the second CP position in the wild-type Escherichia coli ATCase structure complexed with CP. It is suggested that this position may also be in the path that CP takes when binding to the active site in a partial diffusion process at 310 K. Additional biochemical studies of carbamoylation and the molecular organization of this enzyme in M. jannaschii will provide further insight into these points.

  17. Structure of the catalytic chain of Methanococcus jannaschii aspartate transcarbamoylase in a hexagonal crystal form: Insights into the path of carbamoyl phosphate to the active site of the enzyme

    Energy Technology Data Exchange (ETDEWEB)

    Vitali J.; Soares A.; Singh, A. K.; Colaneri, M. J.

    2012-05-01

    Crystals of the catalytic chain of Methanococcus jannaschii aspartate transcarbamoylase (ATCase) grew in the presence of the regulatory chain in the hexagonal space group P6{sub 3}22, with one monomer per asymmetric unit. This is the first time that crystals with only one monomer in the asymmetric unit have been obtained; all known structures of the catalytic subunit contain several crystallographically independent monomers. The symmetry-related chains form the staggered dimer of trimers observed in the other known structures of the catalytic subunit. The central channel of the catalytic subunit contains a sulfate ion and a K{sup +} ion as well as a glycerol molecule at its entrance. It is possible that it is involved in channeling carbamoyl phosphate (CP) to the active site of the enzyme. A second sulfate ion near Arg164 is near the second CP position in the wild-type Escherichia coli ATCase structure complexed with CP. It is suggested that this position may also be in the path that CP takes when binding to the active site in a partial diffusion process at 310 K. Additional biochemical studies of carbamoylation and the molecular organization of this enzyme in M. jannaschii will provide further insight into these points.

  18. Catalytic Oligopeptide Synthesis.

    Science.gov (United States)

    Liu, Zijian; Noda, Hidetoshi; Shibasaki, Masakatsu; Kumagai, Naoya

    2018-02-02

    Waste-free catalytic assembly of α-amino acids is fueled by a multiboron catalyst that features a characteristic B 3 NO 2 heterocycle, providing a versatile catalytic protocol wherein functionalized natural α-amino acid units are accommodated and commonly used protecting groups are tolerated. The facile dehydrative conditions eliminate the use of engineered peptide coupling reagents, exemplifying a greener catalytic alternative for peptide coupling. The catalysis is sufficiently robust to enable pentapeptide synthesis, constructing all four amide bond linkages in a catalytic fashion.

  19. A case of asymmetrical arthrogryposis

    International Nuclear Information System (INIS)

    Hageman, G.; Vette, J.K.; Willemse, J.

    1983-01-01

    Following the introduction of the conception that arthrogryposis is a symptom and not a clinical entity, a case of the very rare asymmetric form of neurogenic arthrogryposis is presented. The asymmetry of congenital contractures and weakness is associated with hemihypotrophy. The value of muscular CT-scanning prior to muscle biopsy is demonstrated. Muscular CT-scanning shows the extension of adipose tissue, which has replaced damaged muscles and therby indicates the exact site for muscle biopsy. Since orthopaedic treatment in arthrogryposis can be unrewarding due to severe muscular degeneration, preoperative scanning may provide additional important information on muscular function and thus be of benefit for surgery. The advantage of muscular CT-scanning in other forms of arthrogryposis requires further determination. The differential diagnosis with Werdnig-Hoffmann disease is discussed. (author)

  20. [Acid-base catalysis of chiral Pd complexes: development of novel asymmetric reactions].

    Science.gov (United States)

    Hamashima, Yoshitaka

    2005-10-01

    Using a unique character of the chiral palladium complexes 1 and 2, several types of novel catalytic asymmetric reactions have been developed. In contrast to the conventional Pd(0)-catalyzed reactions, these complexes function as an acid-base catalyst. Thus active methine compounds were activated to form chiral palladium enolates, which underwent the enantioselective Michael reaction and Mannich-type reaction with up to 99% ee. Interestingly, these palladium enolates acted cooperatively with a strong protic acid activating the electrophiles, formed concomitantly during the formation of the enolates, whereby the C-C bond-forming reaction was promoted. In addition, this palladium enolate chemistry was also applicable to the electrophilic asymmetric fluorination reactions, and thus various carbonyl compounds including beta-ketoesters, beta-ketophosphonates, and oxindoles were fluorinated in a highly enantioselective manner (up to 98% ee). It is advantageous that these reactions were carried out in environmentally friendly alcoholic solvents such as ethanol, and exclusion of air and moisture is not necessary.

  1. Asymmetric Organocatalysis and Photoredox Catalysis for the α-Functionalization of Tetrahydroisoquinolines

    KAUST Repository

    Hou, Hong

    2018-03-14

    The asymmetric α‐alkylation of tetrahydroisoquinolines with cyclic ketones has been accomplished in the presence of a combined catalytic system consisting of a visible‐light photoredox catalyst and a chiral primary amine organocatalyst. The desired products were obtained in good yields, high enantioselectivity, and good to excellent diastereoselectivity. (PC: photoredox cycle, EN: enamine cycle).

  2. Chiral bicycle imidazole nucleophilic catalysts: rational design, facile synthesis, and successful application in asymmetric Steglich rearrangement.

    Science.gov (United States)

    Zhang, Zhenfeng; Xie, Fang; Jia, Jia; Zhang, Wanbin

    2010-11-17

    A new type of chiral bicycle imidazole nucleophilic catalyst was rationally designed, facilely synthesized, and successfully applied in an asymmetric Steglich rearrangement with good to excellent yield and enantioselectivity at ambient temperature. Moreover, it can be easily recycled with almost no reduction of catalytic efficiency. This is the first example for the successful chiral imidazole nucleophilic catalyst without H-bonding assistance.

  3. Organizing for Asymmetric Collaboration

    DEFF Research Database (Denmark)

    Nielsen, Jørn Flohr; Sørensen, Henrik B.

    they meet each other. On the contrary, we assume that asymmetry is both important and normal; moreover, asymmetry should be considered to be more complex than economists indicate with their concept of asymmetric information. Thus, the aim of the paper is to explore how asymmetries related to partners...... to support better diagnosis and as a starting point for more detailed analysis, including interpersonal and processual perspectives, Furthermore, we propose how different situations need different kinds of change interventions. Although including asymmetries in interorganizational analysis does add more...

  4. Asymmetric synthesis v.4

    CERN Document Server

    Morrison, James

    1984-01-01

    Asymmetric Synthesis, Volume 4: The Chiral Carbon Pool and Chiral Sulfur, Nitrogen, Phosphorus, and Silicon Centers describes the practical methods of obtaining chiral fragments. Divided into five chapters, this book specifically examines initial chiral transmission and extension. The opening chapter describes the so-called chiral carbon pool, the readily available chiral carbon fragments used as building blocks in synthesis. This chapter also provides a list of 375 chiral building blocks, along with their commercial sources, approximate prices, and methods of synthesis. Schemes involving

  5. Colon Cryptogenesis: Asymmetric Budding

    Science.gov (United States)

    Tan, Chin Wee; Hirokawa, Yumiko; Gardiner, Bruce S.; Smith, David W.; Burgess, Antony W.

    2013-01-01

    The process of crypt formation and the roles of Wnt and cell-cell adhesion signaling in cryptogenesis are not well described; but are important to the understanding of both normal and cancer colon crypt biology. A quantitative 3D-microscopy and image analysis technique is used to study the frequency, morphology and molecular topography associated with crypt formation. Measurements along the colon reveal the details of crypt formation and some key underlying biochemical signals regulating normal colon biology. Our measurements revealed an asymmetrical crypt budding process, contrary to the previously reported symmetrical fission of crypts. 3D immunofluorescence analyses reveals heterogeneity in the subcellular distribution of E-cadherin and β-catenin in distinct crypt populations. This heterogeneity was also found in asymmetrical budding crypts. Singular crypt formation (i.e. no multiple new crypts forming from one parent crypt) were observed in crypts isolated from the normal colon mucosa, suggestive of a singular constraint mechanism to prevent aberrant crypt production. The technique presented improves our understanding of cryptogenesis and suggests that excess colon crypt formation occurs when Wnt signaling is perturbed (e.g. by truncation of adenomatous polyposis coli, APC protein) in most colon cancers. PMID:24205248

  6. Colon cryptogenesis: asymmetric budding.

    Directory of Open Access Journals (Sweden)

    Chin Wee Tan

    Full Text Available The process of crypt formation and the roles of Wnt and cell-cell adhesion signaling in cryptogenesis are not well described; but are important to the understanding of both normal and cancer colon crypt biology. A quantitative 3D-microscopy and image analysis technique is used to study the frequency, morphology and molecular topography associated with crypt formation. Measurements along the colon reveal the details of crypt formation and some key underlying biochemical signals regulating normal colon biology. Our measurements revealed an asymmetrical crypt budding process, contrary to the previously reported symmetrical fission of crypts. 3D immunofluorescence analyses reveals heterogeneity in the subcellular distribution of E-cadherin and β-catenin in distinct crypt populations. This heterogeneity was also found in asymmetrical budding crypts. Singular crypt formation (i.e. no multiple new crypts forming from one parent crypt were observed in crypts isolated from the normal colon mucosa, suggestive of a singular constraint mechanism to prevent aberrant crypt production. The technique presented improves our understanding of cryptogenesis and suggests that excess colon crypt formation occurs when Wnt signaling is perturbed (e.g. by truncation of adenomatous polyposis coli, APC protein in most colon cancers.

  7. Asymmetric quantum cloning machines

    International Nuclear Information System (INIS)

    Cerf, N.J.

    1998-01-01

    A family of asymmetric cloning machines for quantum bits and N-dimensional quantum states is introduced. These machines produce two approximate copies of a single quantum state that emerge from two distinct channels. In particular, an asymmetric Pauli cloning machine is defined that makes two imperfect copies of a quantum bit, while the overall input-to-output operation for each copy is a Pauli channel. A no-cloning inequality is derived, characterizing the impossibility of copying imposed by quantum mechanics. If p and p ' are the probabilities of the depolarizing channels associated with the two outputs, the domain in (√p,√p ' )-space located inside a particular ellipse representing close-to-perfect cloning is forbidden. This ellipse tends to a circle when copying an N-dimensional state with N→∞, which has a simple semi-classical interpretation. The symmetric Pauli cloning machines are then used to provide an upper bound on the quantum capacity of the Pauli channel of probabilities p x , p y and p z . The capacity is proven to be vanishing if (√p x , √p y , √p z ) lies outside an ellipsoid whose pole coincides with the depolarizing channel that underlies the universal cloning machine. Finally, the tradeoff between the quality of the two copies is shown to result from a complementarity akin to Heisenberg uncertainty principle. (author)

  8. Asymmetric Aminalization via Cation-Binding Catalysis

    DEFF Research Database (Denmark)

    Park, Sang Yeon; Liu, Yidong; Oh, Joong Suk

    2018-01-01

    Asymmetric cation-binding catalysis, in principle, can generate "chiral" anionic nucleophiles, where the counter cations are coordinated within chiral environments. Nitrogen-nucleophiles are intrinsically basic, therefore, its use as nucleophiles is often challenging and limiting the scope...... of the reaction. Particularly, a formation of configurationally labile aminal centers with alkyl substituents has been a formidable challenge due to the enamine/imine equilibrium of electrophilic substrates. Herein, we report enantioselective nucleophilic addition reactions of potassium phthalimides to Boc-protected...

  9. Symmetric Decomposition of Asymmetric Games.

    Science.gov (United States)

    Tuyls, Karl; Pérolat, Julien; Lanctot, Marc; Ostrovski, Georg; Savani, Rahul; Leibo, Joel Z; Ord, Toby; Graepel, Thore; Legg, Shane

    2018-01-17

    We introduce new theoretical insights into two-population asymmetric games allowing for an elegant symmetric decomposition into two single population symmetric games. Specifically, we show how an asymmetric bimatrix game (A,B) can be decomposed into its symmetric counterparts by envisioning and investigating the payoff tables (A and B) that constitute the asymmetric game, as two independent, single population, symmetric games. We reveal several surprising formal relationships between an asymmetric two-population game and its symmetric single population counterparts, which facilitate a convenient analysis of the original asymmetric game due to the dimensionality reduction of the decomposition. The main finding reveals that if (x,y) is a Nash equilibrium of an asymmetric game (A,B), this implies that y is a Nash equilibrium of the symmetric counterpart game determined by payoff table A, and x is a Nash equilibrium of the symmetric counterpart game determined by payoff table B. Also the reverse holds and combinations of Nash equilibria of the counterpart games form Nash equilibria of the asymmetric game. We illustrate how these formal relationships aid in identifying and analysing the Nash structure of asymmetric games, by examining the evolutionary dynamics of the simpler counterpart games in several canonical examples.

  10. Preparation of asymmetric porous materials

    Science.gov (United States)

    Coker, Eric N [Albuquerque, NM

    2012-08-07

    A method for preparing an asymmetric porous material by depositing a porous material film on a flexible substrate, and applying an anisotropic stress to the porous media on the flexible substrate, where the anisotropic stress results from a stress such as an applied mechanical force, a thermal gradient, and an applied voltage, to form an asymmetric porous material.

  11. Asymmetric Effects on Escape Rates of Bistable System

    International Nuclear Information System (INIS)

    Wang Canjun; Mei Dongcheng; Dai Zucheng

    2011-01-01

    The asymmetric effects on the escape rates from the stable states x ± in the bistable system are analyzed. The results indicate that the multiplicative noise and the additive noise always enhance the particle escape from stable states x ± of bistable. However, the asymmetric parameter r enhances the particle escape from stable state x + , and holds back the particle escape from stable state x - . (general)

  12. Non-Classical C–H···X Hydrogen Bonding and Its Role in Asymmetric Organocatalysis

    KAUST Repository

    Ajitha, Manjaly John

    2016-08-17

    Non-classical hydrogen bonds (NCHBs) have attracted significant interest in the past decade particularly because of their important role in asymmetric catalytic systems. These weak interactions (< 4 kcal/mol) offer much flexibility in the preorganization of molecular entities required to achieve high enantioselectivity. Herein, we review some recent important organocatalytic asymmetric reactions where a NCHB serves as a critical factor in determining the stereoselectivity.

  13. Asymmetric Higgsino dark matter.

    Science.gov (United States)

    Blum, Kfir; Efrati, Aielet; Grossman, Yuval; Nir, Yosef; Riotto, Antonio

    2012-08-03

    In the supersymmetric framework, prior to the electroweak phase transition, the existence of a baryon asymmetry implies the existence of a Higgsino asymmetry. We investigate whether the Higgsino could be a viable asymmetric dark matter candidate. We find that this is indeed possible. Thus, supersymmetry can provide the observed dark matter abundance and, furthermore, relate it with the baryon asymmetry, in which case the puzzle of why the baryonic and dark matter mass densities are similar would be explained. To accomplish this task, two conditions are required. First, the gauginos, squarks, and sleptons must all be very heavy, such that the only electroweak-scale superpartners are the Higgsinos. With this spectrum, supersymmetry does not solve the fine-tuning problem. Second, the temperature of the electroweak phase transition must be low, in the (1-10) GeV range. This condition requires an extension of the minimal supersymmetric standard model.

  14. Asymmetric black dyonic holes

    Directory of Open Access Journals (Sweden)

    I. Cabrera-Munguia

    2015-04-01

    Full Text Available A 6-parametric asymptotically flat exact solution, describing a two-body system of asymmetric black dyons, is studied. The system consists of two unequal counterrotating Kerr–Newman black holes, endowed with electric and magnetic charges which are equal but opposite in sign, separated by a massless strut. The Smarr formula is generalized in order to take into account their contribution to the mass. The expressions for the horizon half-length parameters σ1 and σ2, as functions of the Komar parameters and of the coordinate distance, are displayed, and the thermodynamic properties of the two-body system are studied. Furthermore, the seven physical parameters satisfy a simple algebraic relation which can be understood as a dynamical scenario, in which the physical properties of one body are affected by the ones of the other body.

  15. Palladium-catalyzed asymmetric alkylation in the synthesis of cyclopentanoid and cycloheptanoid core structures bearing all-carbon quaternary stereocenters

    KAUST Repository

    Hong, Allen Y.

    2011-12-01

    General catalytic asymmetric routes toward cyclopentanoid and cycloheptanoid core structures embedded in numerous natural products have been developed. The central stereoselective transformation in our divergent strategies is the enantioselective decarboxylative alkylation of seven-membered β-ketoesters to form α-quaternary vinylogous esters. Recognition of the unusual reactivity of β-hydroxyketones resulting from the addition of hydride or organometallic reagents enabled divergent access to γ-quaternary acylcyclopentenes through a ring contraction pathway or γ-quaternary cycloheptenones through a carbonyl transposition pathway. Synthetic applications of these compounds were explored through the preparation of mono-, bi-, and tricyclic derivatives that can serve as valuable intermediates for the total synthesis of complex natural products. This work complements our previous work with cyclohexanoid systems.

  16. Catalytic distillation process

    Science.gov (United States)

    Smith, L.A. Jr.

    1982-06-22

    A method is described for conducting chemical reactions and fractionation of the reaction mixture comprising feeding reactants to a distillation column reactor into a feed zone and concurrently contacting the reactants with a fixed bed catalytic packing to concurrently carry out the reaction and fractionate the reaction mixture. For example, a method for preparing methyl tertiary butyl ether in high purity from a mixed feed stream of isobutene and normal butene comprising feeding the mixed feed stream to a distillation column reactor into a feed zone at the lower end of a distillation reaction zone, and methanol into the upper end of said distillation reaction zone, which is packed with a properly supported cationic ion exchange resin, contacting the C[sub 4] feed and methanol with the catalytic distillation packing to react methanol and isobutene, and concurrently fractionating the ether from the column below the catalytic zone and removing normal butene overhead above the catalytic zone.

  17. Catalytic Functions of Standards

    NARCIS (Netherlands)

    K. Blind (Knut)

    2009-01-01

    textabstractThe three different areas and the examples have illustrated several catalytic functions of standards for innovation. First, the standardisation process reduces the time to market of inventions, research results and innovative technologies. Second, standards themselves promote the

  18. Catalytic distillation structure

    Science.gov (United States)

    Smith, L.A. Jr.

    1984-04-17

    Catalytic distillation structure is described for use in reaction distillation columns, and provides reaction sites and distillation structure consisting of a catalyst component and a resilient component intimately associated therewith. The resilient component has at least about 70 volume % open space and is present with the catalyst component in an amount such that the catalytic distillation structure consists of at least 10 volume % open space. 10 figs.

  19. Palladium-Catalyzed Asymmetric Conjugate Addition of Arylboronic Acids to Five-, Six-, and Seven-Membered β-Substituted Cyclic Enones: Enantioselective Construction of All-Carbon Quaternary Stereocenters

    KAUST Repository

    Kikushima, Kotaro

    2011-05-11

    The first enantioselective Pd-catalyzed construction of all-carbon quaternary stereocenters via 1,4-addition of arylboronic acids to β-substituted cyclic enones is reported. Reaction of a wide range of arylboronic acids and cyclic enones using a catalyst prepared from Pd(OCOCF(3))(2) and a chiral pyridinooxazoline ligand yields enantioenriched products bearing benzylic stereocenters. Notably, this transformation is tolerant to air and moisture, providing a practical and operationally simple method of synthesizing enantioenriched all-carbon quaternary stereocenters.

  20. [Biomechanic of the asymmetrical headgear].

    Science.gov (United States)

    Sander, F G

    1990-11-01

    The asymmetrical headgear is a very useful treatment device for the unilateral distalisation of molars or for the correction of an unilateral anchorage loss. 1. The dimension of the asymmetrical effect depends on the configuration of the outer bows. 2. The function of an asymmetrical face-bow can be increased or decreased by eccentric bendings. 3. According to the geometry at the outer-bows the force at the outer-bow is divided at a different percentage onto the molars. 4. While the forces increase the asymmetrical effect will decrease when the outer-bow is too flexible. 5. Attention has to be payed at each control-appointment to the distance of the longer outer-bow to the cheek. 6. The asymmetrical swivel face-bow did not produce a greater asymmetrical function than other asymmetrical headgears. The reason of this fact is, that only the geometry of the outer-bows is responsible for the unilateral distalisation. 7. The asymmetrical swivel face-bow as described above is advisable to use because eccentric bendings and less forces at the outer-bows will decrease, stop or even reverse the asymmetrical effect. 8. The side-effect of any asymmetrical face-bow is a lateral force-component. This force-component can cause a cross-bite at the molar which has to be more distalized. The molar which is not be moved by the asymmetrical face-bow will be moved buccally by this force-component. 9. The swivel face-bow according to Sander prevents the buccal movement of the molar which should not be moved. But the tendency to create a cross-bite for the molar which should be more distalized, increases. 10. The swivel face-bow according to Sander can be combined with all well-known extraoral tractions. 11. Equal forces at the outer-bows can be reached while using a cervical-pull neckstrap according to Sander. 12. The asymmetrical face-bow and the bite-jumping-appliance can be used simultaneously if the face-bow inserts directly into the attachments of the molar bands.

  1. Performance evaluation of HTTP/TCP on asymmetric networks

    Science.gov (United States)

    Hasegawa, Go; Murata, Masayuki; Miyahara, Hideo

    1999-08-01

    As the Internet users grow, new network technologies are emerging. Those include ADSL and CATV Internet, which essentially provide asymmetric bandwidth for uplink and downlink to the user's connection. In this paper, we investigate the behavior of HTTP/TCP protocols on such asymmetric networks, and present the analytic results of the mean throughput of TCP. The transfer time of Web documents by HTTP over TCP is also derived. In the analysis, we consider newer HTTP/TCP protocols, HTTP/1.1 and TCP Vegas, in addition to HTTP/1.0 and TCP Tahoe. We then investigate the appropriate combination of HTTP and TCP protocols on the asymmetric network. The results show that the effect of HTTP/1.1 is quite small, but TCP Vegas can improve the performance in asymmetric networks if it is appropriately modified as in our proposal.

  2. Defeating the Modern Asymmetric Threat

    National Research Council Canada - National Science Library

    Connor, Robert

    2002-01-01

    ...) ending a horrific 19 year-old low-intensity conflict, Over the course of nearly two decades, the LTTE came to exemplify the modern asymmetric threat as they battled the Sri Lankan Armed Forces (SLAF...

  3. Molecular catalytic coal liquid conversion

    Energy Technology Data Exchange (ETDEWEB)

    Stock, L.M.; Yang, Shiyong [Univ. of Chicago, IL (United States)

    1995-12-31

    This research, which is relevant to the development of new catalytic systems for the improvement of the quality of coal liquids by the addition of dihydrogen, is divided into two tasks. Task 1 centers on the activation of dihydrogen by molecular basic reagents such as hydroxide ion to convert it into a reactive adduct (OH{center_dot}H{sub 2}){sup {minus}} that can reduce organic molecules. Such species should be robust withstanding severe conditions and chemical poisons. Task 2 is focused on an entirely different approach that exploits molecular catalysts, derived from organometallic compounds that are capable of reducing monocyclic aromatic compounds under very mild conditions. Accomplishments and conclusions are discussed.

  4. Asymmetric cation-binding catalysis

    DEFF Research Database (Denmark)

    Oliveira, Maria Teresa; Lee, Jiwoong

    2017-01-01

    solvents, thus increasing their applicability in synthesis. The expansion of this concept to chiral polyethers led to the emergence of asymmetric cation-binding catalysis, where chiral counter anions are generated from metal salts, particularly using BINOL-based polyethers. Alkali metal salts, namely KF...... and KCN, are selectively bound to the catalyst, providing exceptionally high enantioselectivities for kinetic resolutions, elimination reactions (fluoride base), and Strecker synthesis (cyanide nucleophile). Asymmetric cation-binding catalysis was recently expanded to silicon-based reagents, enabling...

  5. Asymmetric Flexible Supercapacitor Stack

    Directory of Open Access Journals (Sweden)

    Leela Mohana Reddy A

    2008-01-01

    Full Text Available AbstractElectrical double layer supercapacitor is very significant in the field of electrical energy storage which can be the solution for the current revolution in the electronic devices like mobile phones, camera flashes which needs flexible and miniaturized energy storage device with all non-aqueous components. The multiwalled carbon nanotubes (MWNTs have been synthesized by catalytic chemical vapor deposition technique over hydrogen decrepitated Mischmetal (Mm based AB3alloy hydride. The polymer dispersed MWNTs have been obtained by insitu polymerization and the metal oxide/MWNTs were synthesized by sol-gel method. Morphological characterizations of polymer dispersed MWNTs have been carried out using scanning electron microscopy (SEM, transmission electron microscopy (TEM and HRTEM. An assymetric double supercapacitor stack has been fabricated using polymer/MWNTs and metal oxide/MWNTs coated over flexible carbon fabric as electrodes and nafion®membrane as a solid electrolyte. Electrochemical performance of the supercapacitor stack has been investigated using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy.

  6. Asymmetric Gepner models (revisited)

    Energy Technology Data Exchange (ETDEWEB)

    Gato-Rivera, B. [NIKHEF Theory Group, Kruislaan 409, 1098 SJ Amsterdam (Netherlands)] [Instituto de Fisica Fundamental, CSIC, Serrano 123, Madrid 28006 (Spain); Schellekens, A.N., E-mail: t58@nikhef.n [NIKHEF Theory Group, Kruislaan 409, 1098 SJ Amsterdam (Netherlands)] [Instituto de Fisica Fundamental, CSIC, Serrano 123, Madrid 28006 (Spain)] [IMAPP, Radboud Universiteit, Nijmegen (Netherlands)

    2010-12-11

    We reconsider a class of heterotic string theories studied in 1989, based on tensor products of N=2 minimal models with asymmetric simple current invariants. We extend this analysis from (2,2) and (1,2) spectra to (0,2) spectra with SO(10) broken to the Standard Model. In the latter case the spectrum must contain fractionally charged particles. We find that in nearly all cases at least some of them are massless. However, we identify a large subclass where the fractional charges are at worst half-integer, and often vector-like. The number of families is very often reduced in comparison to the 1989 results, but there are no new tensor combinations yielding three families. All tensor combinations turn out to fall into two classes: those where the number of families is always divisible by three, and those where it is never divisible by three. We find an empirical rule to determine the class, which appears to extend beyond minimal N=2 tensor products. We observe that distributions of physical quantities such as the number of families, singlets and mirrors have an interesting tendency towards smaller values as the gauge groups approaches the Standard Model. We compare our results with an analogous class of free fermionic models. This displays similar features, but with less resolution. Finally we present a complete scan of the three family models based on the triply-exceptional combination (1,16{sup *},16{sup *},16{sup *}) identified originally by Gepner. We find 1220 distinct three family spectra in this case, forming 610 mirror pairs. About half of them have the gauge group SU(3)xSU(2){sub L}xSU(2){sub R}xU(1){sup 5}, the theoretical minimum, and many others are trinification models.

  7. Palladium-Catalyzed Asymmetric Benzylic Substitution of Secondary Benzyl Carbonates with Nitrogen and Oxygen Nucleophiles.

    Science.gov (United States)

    Najib, Atifah; Hirano, Koji; Miura, Masahiro

    2017-05-05

    A Pd/(R)-BINAP-catalyzed asymmetric benzylic substitution of secondary benzyl carbonates with amides and amines proceeds to form the corresponding optically active benzylamines in good yields with a high enantiomeric ratio. The reaction occurs in a dynamic kinetic asymmetric transformation (DYKAT) manner. Additionally, the asymmetric Pd catalysis can also be applicable to phenol nucleophiles, thus delivering chiral ethers with acceptable yields and enantioselectivity.

  8. Steam reformer with catalytic combustor

    Science.gov (United States)

    Voecks, Gerald E. (Inventor)

    1990-01-01

    A steam reformer is disclosed having an annular steam reforming catalyst bed formed by concentric cylinders and having a catalytic combustor located at the center of the innermost cylinder. Fuel is fed into the interior of the catalytic combustor and air is directed at the top of the combustor, creating a catalytic reaction which provides sufficient heat so as to maintain the catalytic reaction in the steam reforming catalyst bed. Alternatively, air is fed into the interior of the catalytic combustor and a fuel mixture is directed at the top. The catalytic combustor provides enhanced radiant and convective heat transfer to the reformer catalyst bed.

  9. Catalytic converters in the fireplace

    International Nuclear Information System (INIS)

    Kouki, J.

    1995-01-01

    In addition to selecting the appropriate means of heating and using dry fuel, the amount of harmful emissions contained by flue gases produced by fireplaces can be reduced by technical means. One such option is to use an oxidising catalytic converter. Tests at TTS Institute's Heating Studies Experimental Station have focused on two such converters (dense and coarse) mounted in light-weight iron heating stoves. The ability of the dense catalytic converter to oxidise carbon monoxide gases proved to be good. The concentration of carbon monoxide in the flue gases was reduced by as much as 90 %. Measurements conducted by VTT (Technical Research Centre of Finland) showed that the conversion of other gases, e.g. of methane, was good. The exhaust resistance caused by the dense converter was so great as to necessitate the mounting of a fluegas evacuation fan in the chimney for the purpose of creating sufficient draught. When relying on natural draught, the dense converter requires a chimney of at least 7 metres and a by-pass connection while the fire is being lit. In addition, the converter will have to be constructed to be less dense and this will mean that it's capability to oxidise non-combusted gases will be reduced. The coarse converter did not impair the draught but it's oxidising property was insufficient. With the tests over, the converter was not observed to have become blocked up by impurities

  10. Active Component Migration and Catalytic Properties of Nitrogen Modified Composite Catalytic Materials

    Directory of Open Access Journals (Sweden)

    Miaomiao Li

    2018-03-01

    Full Text Available During the catalytic combustion reaction of methane, the migration of the active species on surface facilitates the catalytic reaction, and the element doping can improve the redox performance of the catalyst. Nitrogen-modified perovskite type composite catalysts were prepared by hydrothermal method and then characterized by X-ray diffractometer (XRD, scanning electron microscopy (SEM, Brunauer-Emmett-Teller (BET, temperature-programmed reductions (TPR, and X-ray photoelectron spectra (XPS. The results revealed that nitrogen sources (urea, biuret, melamine, carbohydrazide, and semicarbazide hydrochloride and nitrogen source addition changed the catalytic performance in physical and chemical properties, the migration of reactive species and the catalytic performance. When the addition amount of semicarbazide hydrochloride was three times that of LaCoO3, the composite catalysts had high Co3+/Co2+ (1.39 and Oads/Olat (15.18 and showed the best catalytic performance: the temperatures that are required for achieving methane conversion of 50% and 90% were 277 and 360 °C, which are more effective than noble metal oxides. Moreover, the in situ diffuse reflectance infrared fourier transform spectroscopy (DRIFTS were applied to elucidate the efficient for CH4 removal and also can further explain the surface reaction mechanism of the composite catalyst during the methane catalytic combustion.

  11. CATALYTIC KINETIC SPECTROPHOTOMETRIC DETERMINATION ...

    African Journals Online (AJOL)

    Preferred Customer

    acetylchlorophosphonazo(CPApA) by hydrogen peroxide in 0.10 M phosphoric acid. A novel catalytic kinetic-spectrophotometric method is proposed for the determination of copper based on this principle. Copper(II) can be determined spectrophotometrically ...

  12. CATALYTIC KINETIC SPECTROPHOTOMETRIC DETERMINATION ...

    African Journals Online (AJOL)

    Based on the property that in 0.12 M sulfuric acid medium titanium(IV) catalyzes the discoloring reaction of DBS-arsenazo oxidized by potassium bromate, a new catalytic kinetic spectrophotometric method for the determination of trace titanium (IV) was developed. The linear range of the determination of titanium is

  13. Copper-catalyzed asymmetric allylic alkylation and asymmetric conjugate addition in natural product synthesis

    NARCIS (Netherlands)

    Huang, Yange

    2013-01-01

    In dit proefschrift wordt de koper-gekatalyseerde hetero AAA en ACA toegepast in de totaalsynthese van een aantal biologisch actieve moleculen. In het tweede deel van dit proefschrift ligt de focus op een nieuwe katalytische asymmetrische route naar 1,4-dieenen met een methyl gesubstitueerd chiraal

  14. Catalytic Organic Transformations Mediated by Actinide Complexes

    Directory of Open Access Journals (Sweden)

    Isabell S. R. Karmel

    2015-10-01

    Full Text Available This review article presents the development of organoactinides and actinide coordination complexes as catalysts for homogeneous organic transformations. This chapter introduces the basic principles of actinide catalysis and deals with the historic development of actinide complexes in catalytic processes. The application of organoactinides in homogeneous catalysis is exemplified in the hydroelementation reactions, such as the hydroamination, hydrosilylation, hydroalkoxylation and hydrothiolation of alkynes. Additionally, the use of actinide coordination complexes for the catalytic polymerization of α-olefins and the ring opening polymerization of cyclic esters is presented. The last part of this review article highlights novel catalytic transformations mediated by actinide compounds and gives an outlook to the further potential of this field.

  15. Extremal asymmetric universal cloning machines

    Science.gov (United States)

    Jiang, Mingming; Yu, Sixia

    2010-05-01

    The trade-offs among various output fidelities of asymmetric universal cloning machines are investigated. First we find out all the attainable optimal output fidelities for the 1 to 3 asymmetric universal cloning machine and it turns out that there are two kinds of extremal machines which have to cooperate in order to achieve some of the optimal output fidelities. Second we construct a family of extremal cloning machines that includes the universal symmetric cloning machine as well as an asymmetric 1 to 1+N cloning machine for qudits with two different output fidelities such that the optimal trade-off between the measurement disturbance and state estimation is attained in the limit of infinite N.

  16. Does asymmetric correlation affect portfolio optimization?

    Science.gov (United States)

    Fryd, Lukas

    2017-07-01

    The classical portfolio optimization problem does not assume asymmetric behavior of relationship among asset returns. The existence of asymmetric response in correlation on the bad news could be important information in portfolio optimization. The paper applies Dynamic conditional correlation model (DCC) and his asymmetric version (ADCC) to propose asymmetric behavior of conditional correlation. We analyse asymmetric correlation among S&P index, bonds index and spot gold price before mortgage crisis in 2008. We evaluate forecast ability of the models during and after mortgage crisis and demonstrate the impact of asymmetric correlation on the reduction of portfolio variance.

  17. Ideal 3D asymmetric concentrator

    Energy Technology Data Exchange (ETDEWEB)

    Garcia-Botella, Angel [Departamento Fisica Aplicada a los Recursos Naturales, Universidad Politecnica de Madrid, E.T.S.I. de Montes, Ciudad Universitaria s/n, 28040 Madrid (Spain); Fernandez-Balbuena, Antonio Alvarez; Vazquez, Daniel; Bernabeu, Eusebio [Departamento de Optica, Universidad Complutense de Madrid, Fac. CC. Fisicas, Ciudad Universitaria s/n, 28040 Madrid (Spain)

    2009-01-15

    Nonimaging optics is a field devoted to the design of optical components for applications such as solar concentration or illumination. In this field, many different techniques have been used for producing reflective and refractive optical devices, including reverse engineering techniques. In this paper we apply photometric field theory and elliptic ray bundles method to study 3D asymmetric - without rotational or translational symmetry - concentrators, which can be useful components for nontracking solar applications. We study the one-sheet hyperbolic concentrator and we demonstrate its behaviour as ideal 3D asymmetric concentrator. (author)

  18. Mo-catalyzed asymmetric olefin metathesis in target-oriented synthesis: Enantioselective synthesis of (+)-africanol

    Science.gov (United States)

    Weatherhead, Gabriel S.; Cortez, G. A.; Schrock, Richard R.; Hoveyda, Amir H.

    2004-01-01

    Catalytic asymmetric ring-opening metathesis (AROM) provides an efficient method for the synthesis of a variety of optically enriched small organic molecules that cannot be easily prepared by alternative methods. The development of Mo-catalyzed AROM transformations that occur in tandem with ring-closing metathesis are described. The utility of the Mo-catalyzed AROM/ring-closing metathesis is demonstrated through an enantioselective approach to the synthesis of (+)-africanol. PMID:15056762

  19. Rhodium-catalyzed asymmetric hydrogenation of unprotected NH imines assisted by a thiourea.

    Science.gov (United States)

    Zhao, Qingyang; Wen, Jialin; Tan, Renchang; Huang, Kexuan; Metola, Pedro; Wang, Rui; Anslyn, Eric V; Zhang, Xumu

    2014-08-04

    Asymmetric hydrogenation of unprotected NH imines catalyzed by rhodium/bis(phosphine)-thiourea provided chiral amines with up to 97% yield and 95% ee. (1)H NMR studies, coupled with control experiments, implied that catalytic chloride-bound intermediates were involved in the mechanism through a dual hydrogen-bonding interaction. Deuteration experiments proved that the hydrogenation proceeded through a pathway consistent with an imine. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. C2-Symmetric diamines and their derivatives as promising organocatalysts for asymmetric synthesis

    Science.gov (United States)

    Zlotin, S. G.; Kochetkov, S. V.

    2015-11-01

    The review is devoted to the application of C2-symmetric diamines and their derivatives as organocatalysts for asymmetric reactions (aldol, Michael, Mannich, Diels-Alder reactions, desymmetrization, allylation, etc.). Amino acid derivatives, di- and polyamides (sulfamides), bisureas, bisthioureas, bisamidines and bisguanidines are considered. Significant attention is given to the effect of the catalyst structure on the mechanism of catalytic action. Successful applications of such catalysts in enantioselective synthesis of chiral biologically active compounds are summarized. The bibliography includes 181 references.

  1. Catalytic thermal barrier coatings

    Science.gov (United States)

    Kulkarni, Anand A.; Campbell, Christian X.; Subramanian, Ramesh

    2009-06-02

    A catalyst element (30) for high temperature applications such as a gas turbine engine. The catalyst element includes a metal substrate such as a tube (32) having a layer of ceramic thermal barrier coating material (34) disposed on the substrate for thermally insulating the metal substrate from a high temperature fuel/air mixture. The ceramic thermal barrier coating material is formed of a crystal structure populated with base elements but with selected sites of the crystal structure being populated by substitute ions selected to allow the ceramic thermal barrier coating material to catalytically react the fuel-air mixture at a higher rate than would the base compound without the ionic substitutions. Precious metal crystallites may be disposed within the crystal structure to allow the ceramic thermal barrier coating material to catalytically react the fuel-air mixture at a lower light-off temperature than would the ceramic thermal barrier coating material without the precious metal crystallites.

  2. Carboxy-directed asymmetric hydrogenation of α-alkyl-α-aryl terminal olefins: highly enantioselective and chemoselective access to a chiral benzylmethyl center.

    Science.gov (United States)

    Yang, Shuang; Zhu, Shou-Fei; Guo, Na; Song, Song; Zhou, Qi-Lin

    2014-04-07

    A carboxy-directed asymmetric hydrogenation of α-alkyl-α-aryl terminal olefins was developed by using a chiral spiro iridium catalyst, providing a highly efficient approach to the compounds with a chiral benzylmethyl center. The carboxy-directed hydrogenation prohibited the isomerization of the terminal olefins, and realized the chemoselective hydrogenation of various dienes. The concise enantioselective syntheses of (S)-curcudiol and (S)-curcumene were achieved by using this catalytic asymmetric hydrogenation as a key step.

  3. JET and COMPASS asymmetrical disruptions

    Czech Academy of Sciences Publication Activity Database

    Gerasimov, S.N.; Abreu, P.; Baruzzo, M.; Drozdov, V.; Dvornova, A.; Havlíček, Josef; Hender, T.C.; Hronová-Bilyková, Olena; Kruezi, U.; Li, X.; Markovič, Tomáš; Pánek, Radomír; Rubinacci, G.; Tsalas, M.; Ventre, S.; Villone, F.; Zakharov, L.E.

    2015-01-01

    Roč. 55, č. 11 (2015), s. 113006-113006 ISSN 0029-5515 R&D Projects: GA MŠk(CZ) LM2011021 Institutional support: RVO:61389021 Keywords : tokamak * asymmetrical disruption * JET * COMPASS Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 4.040, year: 2015

  4. Catalytic Membranes Embedding Selective Catalysts: Preparation and Applications

    Science.gov (United States)

    Drioli, Enrico; Fontananova, Enrica

    The embedding of a catalyst in membranes is today recognized as a promising strategy to develop highly efficient and eco-friendly heterogeneous catalytic chemical processes. When a catalyst is heterogenized within or on the surface of a membrane, the membrane composition (characteristics of the membrane material: hydrophobic or hydrophilic, presence of chemical groups with specific functionality, etc.) and the membrane structure (dense or porous, symmetric or asymmetric), can positively influence the catalyst performance, not only by the selective sorption and diffusion of reagents and/or products, but also influencing the catalyst activity by electronic and conformational effect. These effects are similar to those occurring in biological membranes. In this chapter, after a preliminary presentation of the basic principles of membrane reactors and polymer membranes, the preparation, characterization and applications of polymeric catalytic membranes, will be discussed.

  5. Polymer and Membrane Design for Low Temperature Catalytic Reactions

    KAUST Repository

    Villalobos, Luis Francisco

    2016-02-29

    Catalytically active asymmetric membranes have been developed with high loadings of palladium nanoparticles located solely in the membrane\\'s ultrathin skin layer. The manufacturing of these membranes requires polymers with functional groups, which can form insoluble complexes with palladium ions. Three polymers have been synthesized for this purpose and a complexation/nonsolvent induced phase separation followed by a palladium reduction step is carried out to prepare such membranes. Parameters to optimize the skin layer thickness and porosity, the palladium loading in this layer, and the palladium nanoparticles size are determined. The catalytic activity of the membranes is verified with the reduction of a nitro-compound and with a liquid phase Suzuki-Miyaura coupling reaction. Very low reaction times are observed. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Effect of entry bending moment on exit curvature in asymmetrical ...

    African Journals Online (AJOL)

    In addition, employing a bending moment at entry of the roll gap in a symmetrical rolling process causes pressure difference on the rolls and warping at the outlet, as happens in an asymmetrical rolling process. Similarly, increasing the roll diameter ratio increases the pressure differences, but the average pressure between ...

  7. Synthesis of carbon nanotube (CNT)-entangled CuO nanotube networks via CNT-catalytic growth and in situ thermal oxidation as additive-free anodes for lithium ion batteries

    Science.gov (United States)

    Cui, Xia; Song, Bo; Cheng, Shisu; Xie, Yun; Shao, Yijiang; Sun, Yueming

    2018-01-01

    We demonstrated the utility of carbon nanotubes (CNTs) as a catalyst and conductive agent to synthesize CNT-entangled copper nanowire (CuNW-CNT) networks within a melted mixture of hexadecylamine and cetyltrimethy ammounium bromide. The CuNW-CNT networks were further in situ thermally oxidized into CuO nanotube-CNT (CuONT-CNT) with the high retention of network structure. The binder- and conducting-additive-free anodes constructed using the CuONT-CNT networks exhibited high performance, such as high capability (557.7 mAh g‑1 at 0.2 °C after 200 cycles), high Coulombic efficiency (near 100%), good rate performance (385.5 mAh g‑1 at 5 °C and 310.3 mAh g‑1 at 10 °C), and long cycling life.

  8. Cyclodextrins in Asymmetric and Stereospecific Synthesis

    Directory of Open Access Journals (Sweden)

    Fliur Macaev

    2015-09-01

    Full Text Available Since their discovery, cyclodextrins have widely been used as green and easily available alternatives to promoters or catalysts of different chemical reactions in water. This review covers the research and application of cyclodextrins and their derivatives in asymmetric and stereospecific syntheses, with their division into three main groups: (1 cyclodextrins promoting asymmetric and stereospecific catalysis in water; (2 cyclodextrins’ complexes with transition metals as asymmetric and stereospecific catalysts; and (3 cyclodextrins’ non-metallic derivatives as asymmetric and stereospecific catalysts. The scope of this review is to systematize existing information on the contribution of cyclodextrins to asymmetric and stereospecific synthesis and, thus, to facilitate further development in this direction.

  9. Allenes in Asymmetric Catalysis. Asymmetric Ring-Opening of Meso-Epoxides Catalyzed by Allene-Containing Phosphine Oxides

    Science.gov (United States)

    Pu, Xiaotao; Qi, Xiangbing; Ready, Joseph M.

    2009-01-01

    Unsymmetrically substituted allenes (1,2 dienes) are inherently chiral and can be prepared in optically pure form. Nonetheless, to date the allene framework has not been incorporated into ligands for asymmetric catalysis. Since allenes project functionality differently than either tetrahedral carbon or chiral biaryls, they may create complementary chiral environments. This study demonstrates that optically active C2 symmetric allene-containing bisphosphine oxides can catalyze the addition of SiCl4 to meso epoxides with high enantioselectivity. The epoxide-opening likely involves generation of a Lewis acidic, cationic (bisphosphine oxide)SiCl3 complex. The fact that high asymmetric induction is observed suggests that allenes may represent a new platform for the development of ligands and catalysts for asymmetric synthesis. PMID:19722613

  10. [Asymmetric hypertrophy of the masticatory muscles].

    Science.gov (United States)

    Arzul, L; Corre, P; Khonsari, R H; Mercier, J-M; Piot, B

    2012-06-01

    Hypertrophy of the masticatory muscles most commonly affects the masseter. Less common cases of isolated or associated temporalis hypertrophy are also reported. Parafunctional habits, and more precisely bruxism, can favor the onset of the hypertrophy. This condition is generally idiopathic and can require both medical and/or surgical management. A 29-year-old patient was referred to our department for an asymmetric swelling of the masticatory muscles. Physical examination revealed a bilateral hypertrophy of the masticatory muscles, predominantly affecting the right temporalis and the left masseter. Major bruxism was assessed by premature dental wearing. The additional examinations confirmed the isolated muscle hypertrophy. Benign asymmetric hypertrophy of the masticatory muscles promoted by bruxism was diagnosed. Treatment with injections of type A botulinum toxin was conducted in association with a splint and relaxation. Its effectiveness has been observed at six months. Few cases of unilateral or bilateral temporalis hypertrophy have been reported, added to the more common isolated masseter muscles hypertrophy. The diagnosis requires to rule out secondary hypertrophies and tumors using Magnetic Resonance Imaging. The condition is thought to be favoured by parafunctional habits such as bruxism. The conservative treatment consists in reducing the volume of the masticatory muscles using intramuscular injections of type A botulinum toxin. Other potential conservative treatments are wearing splints and muscle relaxant drugs. Surgical procedures aiming to reduce the muscle volume and/or the bone volume (mandibular gonioplasty) can be proposed. Copyright © 2012 Elsevier Masson SAS. All rights reserved.

  11. Catalytic reforming methods

    Science.gov (United States)

    Tadd, Andrew R; Schwank, Johannes

    2013-05-14

    A catalytic reforming method is disclosed herein. The method includes sequentially supplying a plurality of feedstocks of variable compositions to a reformer. The method further includes adding a respective predetermined co-reactant to each of the plurality of feedstocks to obtain a substantially constant output from the reformer for the plurality of feedstocks. The respective predetermined co-reactant is based on a C/H/O atomic composition for a respective one of the plurality of feedstocks and a predetermined C/H/O atomic composition for the substantially constant output.

  12. Helicene-like chiral auxiliaries in asymmetric catalysis.

    Science.gov (United States)

    Aillard, P; Voituriez, A; Marinetti, A

    2014-11-07

    This literature overview demonstrates that helically chiral ligands and organocatalysts have been largely neglected so far. However, a few recent studies on helical pyridine, the corresponding ammonium salts and N-oxides have highlighted the significant potential of these compounds as organocatalysts for Michael type additions, aldehyde propargylations, epoxide openings, and others. In addition, helicenes displaying a fused phosphole ring at the end of their polyaromatic structures, have been used as ligands in enantioselective gold promoted cycloisomerization reactions, giving both excellent catalytic activity and high enantiomeric excesses. These recent results are expected to stimulate further research on the catalytic applications of helically chiral auxiliaries in the next few years.

  13. The central chirality of the metal atom and configurational relations in asymmetric reactions catalysed by metal complexes

    Energy Technology Data Exchange (ETDEWEB)

    Pavlov, Valerii A [N.D.Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow (Russian Federation)

    2004-12-31

    The recently published data on the dependence of the configuration of the reaction product on the structure of a catalytic metal complex (or an intermediate determining the asymmetric induction) in asymmetric catalytic reactions of hydrogen-transfer hydrogenation of acetophenone, hydroformylation of styrene, allylic alkylation of 1,3-diphenylprop-2-enyl acetate and alkylation of benzaldehyde with dialkylzinc are systematised. The applicabilities of octant and quadrant projections of the complexes are compared in order to establish the relationships between their structures and the enantioselectivities of the reactions. The known mechanisms of asymmetric induction in these reactions are discussed with regard to the C{sub 1} or C{sub 2} symmetry of the catalytic complex. The reasons for a decrease in the enantioselectivities of hydrogen-transfer hydrogenation, hydroformylation and alkylation by dialkylzinc [in the absence of Ti(OPr{sup i}){sub 4}] when performed with complexes with chiral C{sub 2}-symmetric ligands (as compared with complexes with asymmetric ligands) are considered.

  14. Stable walking with asymmetric legs

    International Nuclear Information System (INIS)

    Merker, Andreas; Rummel, Juergen; Seyfarth, Andre

    2011-01-01

    Asymmetric leg function is often an undesired side-effect in artificial legged systems and may reflect functional deficits or variations in the mechanical construction. It can also be found in legged locomotion in humans and animals such as after an accident or in specific gait patterns. So far, it is not clear to what extent differences in the leg function of contralateral limbs can be tolerated during walking or running. Here, we address this issue using a bipedal spring-mass model for simulating walking with compliant legs. With the help of the model, we show that considerable differences between contralateral legs can be tolerated and may even provide advantages to the robustness of the system dynamics. A better understanding of the mechanisms and potential benefits of asymmetric leg operation may help to guide the development of artificial limbs or the design novel therapeutic concepts and rehabilitation strategies.

  15. Asymmetric Hybrid Nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Chumanov, George [Clemson Univ., SC (United States)

    2015-11-05

    Hybrid Nanoparticles (AHNs) are rationally-designed multifunctional nanostructures and novel building blocks for the next generation of advanced materials and devices. Nanoscale materials attract considerable interest because of their unusual properties and potential for practical applications. Most of the activity in this field is focused on the synthesis of homogeneous nanoparticles from metals, metal oxides, semiconductors, and polymers. It is well recognized that properties of nanoparticles can be further enhanced if they are made as hybrid structures. This program is concerned with the synthesis, characterization, and application of such hybrid structures termed AHNs. AHNs are composed of a homogeneous core and several caps of different materials deposited on its surface (Fig. 1). Combined properties of the core and the caps as well as new properties that arise from core-cap and cap-cap interactions render AHNs multifunctional. In addition, specific chemical reactivity of the caps enables directional self-assembly of AHNs into complex architectures that are not possible with only spherical nanoparticles.

  16. Asymmetric information and macroeconomic dynamics

    Science.gov (United States)

    Hawkins, Raymond J.; Aoki, Masanao; Roy Frieden, B.

    2010-09-01

    We show how macroeconomic dynamics can be derived from asymmetric information. As an illustration of the utility of this approach we derive the equilibrium density, non-equilibrium densities and the equation of motion for the response to a demand shock for productivity in a simple economy. Novel consequences of this approach include a natural incorporation of time dependence into macroeconomics and a common information-theoretic basis for economics and other fields seeking to link micro-dynamics and macro-observables.

  17. Asymmetric Wettability Directs Leidenfrost Droplets

    Energy Technology Data Exchange (ETDEWEB)

    Agapov, Rebecca L [ORNL; Boreyko, Jonathan B [ORNL; Briggs, Dayrl P [ORNL; Srijanto, Bernadeta R [ORNL; Retterer, Scott T [ORNL; Collier, Pat [ORNL; Lavrik, Nickolay V [ORNL

    2014-01-01

    Leidenfrost phenomena on nano- and microstructured surfaces are of great importance for increasing control over heat transfer in high power density systems utilizing boiling phenomena. They also provide an elegant means to direct droplet motion in a variety of recently emerging fluidic systems. Here, we report the fabrication and characterization of tilted nanopillar arrays (TNPAs) that exhibit directional Leidenfrost water droplets under dynamic conditions, namely on impact with Weber numbers 40 at T 325 C. The batch fabrication of the TNPAs was achieved by glancing-angle anisotropic reactive ion etching of a thermally dewet platinum mask, with mean pillar diameters of 100 nm and heights of 200-500 nm. In contrast to previously implemented macro- and microscopic Leidenfrost ratchets, our TNPAs induce no preferential directional movement of Leidenfrost droplets under conditions approaching steady-state film boiling, suggesting that the observed droplet directionality is not a result of asymmetric vapor flow. Using high-speed imaging, phase diagrams were constructed for the boiling behavior upon impact for droplets falling onto TNPAs, straight nanopillar arrays, and smooth silicon surfaces. The asymmetric impact and directional trajectory of droplets was exclusive to the TNPAs for impacts corresponding to the transition boiling regime, revealing that asymmetric wettability upon impact is the mechanism for the droplet directionality.

  18. Vinylimidazole-Based Asymmetric Ion Pair Comonomers: Synthesis, Polymerization Studies and Formation of Ionically Crosslinked PMMA

    NARCIS (Netherlands)

    Jana, S.; Vasantha, V.A.; Stubbs, L.P.; Parthiban, A.; Vancso, Gyula J.

    2013-01-01

    Vinylimidazole-based asymmetric ion pair comonomers (IPCs) which are free from nonpolymerizable counter ions have been synthesized, characterized and polymerized by free radical polymerization (FRP), atom transfer radical polymerization (ATRP), and reversible addition-fragmentation chain transfer

  19. Enhanced propylene production in FCC by novel catalytic materials

    Energy Technology Data Exchange (ETDEWEB)

    Kelkar, C.P.; Harris, D.; Xu, M.; Fu, J. [BASF Catalyst LLC, Iselin, NJ (United States)

    2007-07-01

    Fluid catalytic cracking is expected to increasingly supply the additional incremental requirements for propylene. The most efficient route to increase propylene yield from an FCC unit is through the use of medium pore zeolites such as ZSM-5. ZSM-5 zeolite cracks near linear olefins in the gasoline range to LPG olefins such as propylene and butylenes. This paper will describe catalytic approaches to increase gasoline range olefins and the chemistry of ZSM-5 to crack those olefins. The paper will also describe novel catalytic materials designed to increase propylene. (orig.)

  20. Impact of asymmetric lamp positioning on the performance of a closed-conduit UV reactor

    Directory of Open Access Journals (Sweden)

    Tipu Sultan

    2017-06-01

    Full Text Available Computational fluid dynamics (CFD analyses for the performance improvement of a closed-conduit ultraviolet (UV reactor were performed by changing the lamp positions from symmetric to asymmetric. The asymmetric lamp positioning can be useful for UV reactor design and optimization. This goal was achieved by incorporating the two performance factors, namely reduction equivalent dose (RED and system dose performance. Four cases were carried out for asymmetric lamp positioning within the UV reactor chamber and each case consisted of four UV lamps that were simulated once symmetrically and four times asymmetrically. The results of the four asymmetric cases were compared with the symmetric one. Moreover, these results were evaluated by using CFD simulations of a closed-conduit UV reactor. The fluence rate model, UVCalc3D was employed to validate the simulations results. The simulation results provide detailed information about the dose distribution, pathogen track modeling and RED. The RED value was increased by approximately 15% by using UVCalc3D fluence rate model. Additionally, the asymmetric lamp positioning of the UV lamps had more than 50% of the pathogens received a better and a higher UV dose than in the symmetric case. Consequently, the system dose performance was improved by asymmetric lamp positioning. It was concluded that the performance parameters (higher RED and system dose performance were improved by using asymmetric lamp positioning.

  1. Catalytic Antibodies: Concept and Promise

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 12; Issue 11. Catalytic Antibodies: Concept and Promise. Desirazu N Rao Bharath Wootla. General Article Volume 12 Issue ... Keywords. Catalytic antibodies; abzymes; hybridome technology; Diels– Alder reaction; Michaelis– Menten kinetics; Factor VIII.

  2. Catalytic interface erosion

    International Nuclear Information System (INIS)

    Meng, H.; Cohen, E.G.D.

    1995-01-01

    We study interface erosion processes: catalytic erosions. We present two cases. (1) The erosion of a completely occupied lattice by one single moving particle starting from somewhere inside the lattice, considering deterministic as well as probabilistic erosion rules. In the latter case, the eroded regions appear to have interfaces with continuously tunable fractal dimensions. (2) The kinetic roughening of an initially flat surface, where ballistic or diffusion-limited particles, which remain intact themselves, erode the surface coming from the outside, using the same erosion rules as in (1). Many features resembling realistic interfaces, for example, islands and inlets, are generated. The dependence of the surface width on the system size is due to both the erosion mechanism and the way particles move before reaching the surface

  3. Catalytic detritiation of water

    International Nuclear Information System (INIS)

    Rogers, M.L.; Lamberger, P.H.; Ellis, R.E.; Mills, T.K.

    1977-01-01

    A pilot-scale system has been used at Mound Laboratory to investigate the catalytic detritiation of water. A hydrophobic, precious metal catalyst is used to promote the exchange of tritium between liquid water and gaseous hydrogen at 60 0 C. Two columns are used, each 7.5 m long by 2.5 cm ID and packed with catalyst. Water flow is 5-10 cm 3 /min and countercurrent hydrogen flow is 9,000-12,000 cm 3 /min. The equipment, except for the columns, is housed in an inert atmosphere glovebox and is computer controlled. The hydrogen is obtained by electrolysis of a portion of the water stream. Enriched gaseous tritium is withdrawn for further enrichment. A description of the system is included along with an outline of its operation. Recent experimental data are discussed

  4. Catalytic enantioselective N-nitroso aldol reaction of γ,δ-unsaturated δ-lactones.

    Science.gov (United States)

    Yanagisawa, Akira; Fujinami, Takeo; Oyokawa, Yu; Sugita, Takuya; Yoshida, Kazuhiro

    2012-05-18

    A catalytic asymmetric N-nitroso aldol reaction of γ,δ-didehydro-δ-lactones with nitrosoarenes was achieved using chiral tin dibromide as the chiral precatalyst and sodium ethoxide as the base precatalyst in the presence of ethanol. Optically active α-hydroxyamino ketones with up to 99% ee were regioselectively obtained in moderate to high yields from various δ-aryl-substituted γ,δ-didehydro-δ-valerolactones and o-substituted nitrosoarenes.

  5. Synthesis method of asymmetric gold particles.

    Science.gov (United States)

    Jun, Bong-Hyun; Murata, Michael; Hahm, Eunil; Lee, Luke P

    2017-06-07

    Asymmetric particles can exhibit unique properties. However, reported synthesis methods for asymmetric particles hinder their application because these methods have a limited scale and lack the ability to afford particles of varied shapes. Herein, we report a novel synthetic method which has the potential to produce large quantities of asymmetric particles. Asymmetric rose-shaped gold particles were fabricated as a proof of concept experiment. First, silica nanoparticles (NPs) were bound to a hydrophobic micro-sized polymer containing 2-chlorotritylchloride linkers (2-CTC resin). Then, half-planar gold particles with rose-shaped and polyhedral structures were prepared on the silica particles on the 2-CTC resin. Particle size was controlled by the concentration of the gold source. The asymmetric particles were easily cleaved from the resin without aggregation. We confirmed that gold was grown on the silica NPs. This facile method for synthesizing asymmetric particles has great potential for materials science.

  6. Catalytic Combustion of Gasified Waste

    Energy Technology Data Exchange (ETDEWEB)

    Kusar, Henrik

    2003-09-01

    This thesis concerns catalytic combustion for gas turbine application using a low heating-value (LHV) gas, derived from gasified waste. The main research in catalytic combustion focuses on methane as fuel, but an increasing interest is directed towards catalytic combustion of LHV fuels. This thesis shows that it is possible to catalytically combust a LHV gas and to oxidize fuel-bound nitrogen (NH{sub 3}) directly into N{sub 2} without forming NO{sub x} The first part of the thesis gives a background to the system. It defines waste, shortly describes gasification and more thoroughly catalytic combustion. The second part of the present thesis, paper I, concerns the development and testing of potential catalysts for catalytic combustion of LHV gases. The objective of this work was to investigate the possibility to use a stable metal oxide instead of noble metals as ignition catalyst and at the same time reduce the formation of NO{sub x} In paper II pilot-scale tests were carried out to prove the potential of catalytic combustion using real gasified waste and to compare with the results obtained in laboratory scale using a synthetic gas simulating gasified waste. In paper III, selective catalytic oxidation for decreasing the NO{sub x} formation from fuel-bound nitrogen was examined using two different approaches: fuel-lean and fuel-rich conditions. Finally, the last part of the thesis deals with deactivation of catalysts. The various deactivation processes which may affect high-temperature catalytic combustion are reviewed in paper IV. In paper V the poisoning effect of low amounts of sulfur was studied; various metal oxides as well as supported palladium and platinum catalysts were used as catalysts for combustion of a synthetic gas. In conclusion, with the results obtained in this thesis it would be possible to compose a working catalytic system for gas turbine application using a LHV gas.

  7. Orion EFT-1 Catalytic Tile Experiment Overview and Flight Measurements

    Science.gov (United States)

    Salazar, Giovanni; Amar, Adam; Hyatt, Andrew; Rezin, Marc D.

    2016-01-01

    This paper describes the design and results of a surface catalysis flight experiment flown on the Orion Multipurpose Crew Vehicle during Exploration Flight Test 1 (EFT1). Similar to previous Space Shuttle catalytic tile experiments, the present test consisted of a highly catalytic coating applied to an instrumented TPS tile. However, the present catalytic tile experiment contained significantly more instrumentation in order to better resolve the heating overshoot caused by the change in surface catalytic efficiency at the interface between two distinct materials. In addition to collecting data with unprecedented spatial resolution of the "overshoot" phenomenon, the experiment was also designed to prove if such a catalytic overshoot would be seen in turbulent flow in high enthalpy regimes. A detailed discussion of the results obtained during EFT1 is presented, as well as the challenges associated with data interpretation of this experiment. Results of material testing carried out in support of this flight experiment are also shown. Finally, an inverse heat conduction technique is employed to reconstruct the flight environments at locations upstream and along the catalytic coating. The data and analysis presented in this work will greatly contribute to our understanding of the catalytic "overshoot" phenomenon, and have a significant impact on the design of future spacecraft.

  8. Asymmetric effects in customer satisfaction

    DEFF Research Database (Denmark)

    Füller, Johann; Matzler, Kurt; Faullant, Rita

    2006-01-01

    The results of this study on customer satisfaction in snowboard areas show that the relationship between an attribute and overall satisfaction can indeed be asymmetric. A 30-item self-administered survey was completed by snowboarders (n=2526) in 51 areas in Austria, Germany, Switzerland and Italy....... Results show that waiting time is a dissatisfier; it has a significant impact on overall customer satisfaction in the low satisfaction condition and becomes insignificant in the high satisfaction situation. Restaurants and bars are hybrids, i.e. importance does not depend on performance. Slopes, fun...... and entertainment and employees have a slightly stronger impact when satisfaction is low....

  9. The crystal structure, mutagenesis, and activity studies reveal that patatin is a lipid acyl hydrolase with a Ser-Asp catalytic dyad.

    Science.gov (United States)

    Rydel, Timothy J; Williams, Jennifer M; Krieger, Elysia; Moshiri, Farhad; Stallings, William C; Brown, Sherri M; Pershing, Jay C; Purcell, John P; Alibhai, Murtaza F

    2003-06-10

    Patatin is a nonspecific lipid acyl hydrolase that accounts for approximately 40% of the total soluble protein in mature potato tubers, and it has potent insecticidal activity against the corn rootworm. We determined the X-ray crystal structure of a His-tagged variant of an isozyme of patatin, Pat17, to 2.2 A resolution, employing SeMet multiwavelength anomalous dispersion (MAD) phasing methods. The patatin crystal structure has three molecules in the asymmetric unit, an R-factor of 22.0%, and an R(free) of 27.2% (for 10% of the data not included in the refinement) and includes 498 water molecules. The structure notably revealed that patatin has a Ser-Asp catalytic dyad and an active site like that of human cytosolic phospholipase A(2) (cPLA(2)) [Dessen, A., et al. (1999) Cell 97, 349-360]. In addition, patatin has a folding topology related to that of the catalytic domain of cPLA(2) and unlike the canonical alpha/beta-hydrolase fold. The structure confirms our site-directed mutagenesis and bioactivity data that initially suggested patatin possessed a Ser-Asp catalytic dyad. Alanine-scanning mutagenesis revealed that Ser77 and Asp215 were critical for both esterase and bioactivity, consistent with prior work implicating a Ser residue [Strickland, J. H., et al. (1995) Plant Physiol. 109, 667-674] and a Ser-Asp dyad [Hirschberg, H. J. H. B., et al. (2001) Eur. J. Biochem. 268, 5037-5044] in patatin's catalytic activity. The crystal structure aids the understanding of other structure-function relationships in patatin. Patatin does not display interfacial activation, a hallmark feature of lipases, and this is likely due to the fact that it lacks a flexible lid that can shield the active site.

  10. Effects of different level addition of zeolite ZSM-5 additive on quality and composition of the dry gas, LPG (Liquefied Petroleum Gas) and gasoline, produced in FCC (Fluid Catalytic Cracking); Efeito dos diferentes niveis de adicao de aditivos de ZSM-5 na qualidade e composicao do gas combustivel, GLP e gasolina produzidos em FCC

    Energy Technology Data Exchange (ETDEWEB)

    Bastiani, Raquel; Pimenta, Ricardo D.M.; Almeida, Marlon B.B.; Lau, Lam Y. [PETROBRAS S.A., Rio de Janeiro, RJ (Brazil)

    2004-07-01

    The effects of the addition of different level of ZSM-5 additives on different FCC catalysts formulations have been studied on laboratory scale FST (Fluidized Simulation Test). The main objective of the present work is to perform a qualitative identification of the main parameters of FCC catalyst which affect the ZSM-5 additives performance concerning quality and composition of Dry Gas, LPG and Gasoline. The product composition of each test was analyzed by PIANO groups separated by carbon number. The effect of ZSM-5 on products composition was evaluated. The results showed that the ZSM-5 additive cracks gasoline range olefins and isoparaffins into Dry Gas and LPG, favoring the formation of ethylene, propylene and butylenes, while the absolute yield of gasoline aromatics changes little. The aromatics fraction in gasoline, MON and RON numbers in gasoline increase. The ZSM-5 effectiveness is negatively affected by high levels of rare earth on FCC catalyst (RE-USY). Higher hydrogen transfer provides lower olefins (higher than C6) formation, which are the most reactive species for ZSM-5 cracking. (author)

  11. Catalytic production of biodiesel

    Energy Technology Data Exchange (ETDEWEB)

    Theilgaard Madsen, A.

    2011-07-01

    The focus of this thesis is the catalytic production of diesel from biomass, especially emphasising catalytic conversion of waste vegetable oils and fats. In chapter 1 an introduction to biofuels and a review on different catalytic methods for diesel production from biomass is given. Two of these methods have been used industrially for a number of years already, namely the transesterification (and esterification) of oils and fats with methanol to form fatty acid methyl esters (FAME), and the hydrodeoxygenation (HDO) of fats and oils to form straight-chain alkanes. Other possible routes to diesel include upgrading and deoxygenation of pyrolysis oils or aqueous sludge wastes, condensations and reductions of sugars in aqueous phase (aqueous-phase reforming, APR) for monofunctional hydrocarbons, and gasification of any type of biomass followed by Fischer-Tropsch-synthesis for alkane biofuels. These methods have not yet been industrialised, but may be more promising due to the larger abundance of their potential feedstocks, especially waste feedstocks. Chapter 2 deals with formation of FAME from waste fats and oils. A range of acidic catalysts were tested in a model fat mixture of methanol, lauric acid and trioctanoin. Sulphonic acid-functionalised ionic liquids showed extremely fast convertion of lauric acid to methyl laurate, and trioctanoate was converted to methyl octanoate within 24 h. A catalyst based on a sulphonated carbon-matrix made by pyrolysing (or carbonising) carbohydrates, so-called sulphonated pyrolysed sucrose (SPS), was optimised further. No systematic dependency on pyrolysis and sulphonation conditions could be obtained, however, with respect to esterification activity, but high activity was obtained in the model fat mixture. SPS impregnated on opel-cell Al{sub 2}O{sub 3} and microporous SiO{sub 2} (ISPS) was much less active in the esterification than the original SPS powder due to low loading and thereby low number of strongly acidic sites on the

  12. Instability of asymmetric shaft system

    Science.gov (United States)

    Srinath, R.; Sarkar, Abhijit; Sekhar, A. S.

    2016-02-01

    In the present work, parametric instability of asymmetric shaft mounted on bearings is studied. Towards this end, four different models of increasing complexity are studied. The equations corresponding to these models are formulated in the inertial reference frame. These equations involve a periodically varying coefficient. This is similar to classical Mathieu equation but in a multi-degree of freedom context. As such, under suitable parameter combination these systems result in growing oscillation amplitudes or instability. For wider generalization, the equations and results are presented in a non-dimensional form. The unstable parameter regimes are found using the Floquet theory and perturbation methods. These results are also corroborated with existing results in the literature. The nature of the stability boundary and its dependence on various system parameters is discussed in elaborate detail. The stability boundary can be used to determine unstable operating speed ranges for different asymmetric shaft cross-sections. Further, material, geometry and bearing selection guidelines for ensuring stable operations can be inferred from these results.

  13. Field factors for asymmetric collimators

    International Nuclear Information System (INIS)

    Turner, J.R.; Butler, A.P.H.

    1996-01-01

    In recent years manufacturers have been supplying linear accelerators with either a single pair or a dual pair of collimators. The use of a model to relate off-axis field factors to on-axis field factors obviates the need for repeat measurements whenever the asymmetric collimators are employed. We have investigated the variation of collimator scatter Sc, with distance of the central ray x from the central axis for a variety of non square field sizes. Collimator scatter was measured by in-air measurements with a build-up cap. The Primaty-Off-Centre-Ratio (POCR) was measured in-air by scanning orthogonally across the beam with an ionization chamber. The result of the investigation is the useful prediction of off-axis field factors for a range of rectangular asymmetric fields using the simple product of the on-axis field factor and the POCR in air. The effect of asymmetry on the quality of the beam and hence the percent depth dose will be discussed. (author)

  14. Catalytic cracking with deasphalted oil

    Energy Technology Data Exchange (ETDEWEB)

    Beaton, W.I.; Taylor, J.L.; Peck, L.B.; Mosby, J.F.

    1990-07-10

    This patent describes a catalytic cracking process. It comprises: hydrotreating resid; thereafter deasphalting the hydrotreated resid to produce substantially deasphalted oil; catalytically cracking the hydrotreated oil in a catalytic cracking unit in the presence of a cracking catalyst to produce upgraded oil leaving coked catalyst; and regenerating the coked catalyst in the presence of a combustion-supporting gas comprising excess molecular oxygen in an amount greater than the stoichiometric amount required for substantially completely combusting the coke on the catalyst to carbon dioxide.

  15. Catalytic Membrane Sensors

    Energy Technology Data Exchange (ETDEWEB)

    Boyle, T.J.; Brinker, C.J.; Gardner, T.J.; Hughes, R.C.; Sault, A.G.

    1998-12-01

    The proposed "catalytic membrane sensor" (CMS) was developed to generate a device which would selectively identify a specific reagent in a complex mixture of gases. This was to be accomplished by modifying an existing Hz sensor with a series of thin films. Through selectively sieving the desired component from a complex mixture and identifying it by decomposing it into Hz (and other by-products), a Hz sensor could then be used to detect the presence of the select component. The proposed "sandwich-type" modifications involved the deposition of a catalyst layered between two size selective sol-gel layers on a Pd/Ni resistive Hz sensor. The role of the catalyst was to convert organic materials to Hz and organic by-products. The role of the membraneo was to impart both chemical specificity by molecukir sieving of the analyte and converted product streams, as well as controlling access to the underlying Pd/Ni sensor. Ultimately, an array of these CMS elements encompassing different catalysts and membranes were to be developed which would enable improved selectivity and specificity from a compiex mixture of organic gases via pattern recognition methodologies. We have successfully generated a CMS device by a series of spin-coat deposited methods; however, it was determined that the high temperature required to activate the catalyst, destroys the sensor.

  16. Catalytic cracking of lignites

    Energy Technology Data Exchange (ETDEWEB)

    Seitz, M.; Nowak, S.; Naegler, T.; Zimmermann, J. [Hochschule Merseburg (Germany); Welscher, J.; Schwieger, W. [Erlangen-Nuernberg Univ. (Germany); Hahn, T. [Halle-Wittenberg Univ., Halle (Germany)

    2013-11-01

    A most important factor for the chemical industry is the availability of cheap raw materials. As the oil price of crude oil is rising alternative feedstocks like coal are coming into focus. This work, the catalytic cracking of lignite is part of the alliance ibi (innovative Braunkohlenintegration) to use lignite as a raw material to produce chemicals. With this new one step process without an input of external hydrogen, mostly propylene, butenes and aromatics and char are formed. The product yield depends on manifold process parameters. The use of acid catalysts (zeolites like MFI) shows the highest amount of the desired products. Hydrogen rich lignites with a molar H/C ratio of > 1 are to be favoured. Due to primary cracking and secondary reactions the ratio between catalyst and lignite, temperature and residence time are the most important parameter to control the product distribution. Experiments at 500 C in a discontinuous rotary kiln reactor show yields up to 32 wt-% of hydrocarbons per lignite (maf - moisture and ash free) and 43 wt-% char, which can be gasified. Particularly, the yields of propylene and butenes as main products can be enhanced four times to about 8 wt-% by the use of catalysts while the tar yield decreases. In order to develop this innovative process catalyst systems fixed on beads were developed for an easy separation and regeneration of the used catalyst from the formed char. (orig.)

  17. Asymmetric Synthesis of Spiropyrazolones by Sequential Organo- and Silver Catalysis.

    Science.gov (United States)

    Hack, Daniel; Dürr, Alexander B; Deckers, Kristina; Chauhan, Pankaj; Seling, Nico; Rübenach, Lukas; Mertens, Lucas; Raabe, Gerhard; Schoenebeck, Franziska; Enders, Dieter

    2016-01-26

    A stereoselective one-pot synthesis of spiropyrazolones through an organocatalytic asymmetric Michael addition and a formal Conia-ene reaction has been developed. Depending on the nitroalkene, the 5-exo-dig-cyclization could be achieved by silver-catalyzed alkyne activation or by oxidation of the intermediate enolate. The mechanistic pathways have been investigated using computational chemistry and mechanistic experiments. © 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

  18. Worst Asymmetrical Short-Circuit Current

    DEFF Research Database (Denmark)

    Arana Aristi, Iván; Holmstrøm, O; Grastrup, L

    2010-01-01

    In a typical power plant, the production scenario and the short-circuit time were found for the worst asymmetrical short-circuit current. Then, a sensitivity analysis on the missing generator values was realized in order to minimize the uncertainty of the results. Afterward the worst asymmetrical...

  19. Mechanochemistry assisted asymmetric organocatalysis: A sustainable approach

    Directory of Open Access Journals (Sweden)

    Pankaj Chauhan

    2012-12-01

    Full Text Available Ball-milling and pestle and mortar grinding have emerged as powerful methods for the development of environmentally benign chemical transformations. Recently, the use of these mechanochemical techniques in asymmetric organocatalysis has increased. This review highlights the progress in asymmetric organocatalytic reactions assisted by mechanochemical techniques.

  20. Asymmetric Frontal Brain Activity and Parental Rejection

    NARCIS (Netherlands)

    Huffmeijer, R.; Alink, L.R.A.; Tops, M.; Bakermans-Kranenburg, M.J.; van IJzendoorn, M.H.

    2013-01-01

    Asymmetric frontal brain activity has been widely implicated in reactions to emotional stimuli and is thought to reflect individual differences in approach-withdrawal motivation. Here, we investigate whether asymmetric frontal activity, as a measure of approach-withdrawal motivation, also predicts

  1. Uniform versus asymmetric shading mediates crown recession in conifers.

    Directory of Open Access Journals (Sweden)

    Amanda L Schoonmaker

    Full Text Available In this study we explore the impact of asymmetrical vs. uniform crown shading on the mortality and growth of upper and lower branches within tree crowns, for two conifer species: shade intolerant lodgepole pine (Pinus contorta and shade tolerant white spruce (Picea glauca. We also explore xylem hydraulics, foliar nutrition, and carbohydrate status as drivers for growth and expansion of the lower and upper branches in various types of shading. This study was conducted over a two-year period across 10 regenerating forest sites dominated by lodgepole pine and white spruce, in the lower foothills of Alberta, Canada. Trees were assigned to one of four shading treatments: (1, complete uniform shading of the entire tree, (2 light asymmetric shading where the lower 1/4-1/3 of the tree crown was shaded, (3 heavy asymmetric shading as in (2 except with greater light reduction and (4 control in which no artificial shading occurred and most of the entire crown was exposed to full light. Asymmetrical shading of only the lower crown had a larger negative impact on the bud expansion and growth than did uniform shading, and the effect was stronger in pine relative to spruce. In addition, lower branches in pine also had lower carbon reserves, and reduced xylem-area specific conductivity compared to spruce. For both species, but particularly the pine, the needles of lower branches tended to store less C than upper branches in the asymmetric shade, which could suggest a movement of reserves away from the lower branches. The implications of these findings correspond with the inherent shade tolerance and self-pruning behavior of these conifers and supports a carbon based mechanism for branch mortality--mediated by an asymmetry in light exposure of the crown.

  2. Catalytic pyrolysis of lignocellulosic biomass

    NARCIS (Netherlands)

    Seshan, Kulathuiyer; Sa, Jacinto

    2014-01-01

    This chapter reports on the latest developments of biomass catalytic pyrolysis for the production of fuels. The primary focus is on the role of catalysts in the process, namely, their influence in the liquefaction of lignocellulosic biomass.

  3. Asymmetric synthesis of an axially chiral antimitotic biaryl via an atropo-enantioselective Suzuki cross-coupling.

    Science.gov (United States)

    Herrbach, Audrey; Marinetti, Angela; Baudoin, Olivier; Guénard, Daniel; Guéritte, Françoise

    2003-06-13

    A catalytic asymmetric synthesis of the axially chiral bridged biaryl (-)-2, a structural analogue of natural (-)-rhazinilam possessing original antimitotic properties, is described. The key step is an intermolecular asymmetric Suzuki coupling, furnishing the nonbridged biaryl (-)-6, precursor of (-)-2, with up to 40% ee using binaphthyl ligand 7a. Various known or new binaphthyl and ferrocenyl phosphines as well as phosphetanes were screened as ligands in this reaction, the conditions of which were optimized. The comparison with another Suzuki coupling system showed that 7a is the most versatile ligand described to date for this type of transformation. This work gives the first application of the asymmetric Suzuki coupling to a biologically relevant target.

  4. Packing of soft asymmetric dumbbells.

    Science.gov (United States)

    Sarić, Anđela; Bozorgui, Behnaz; Cacciuto, Angelo

    2011-06-09

    We use numerical simulations to study the phase behavior of a system of purely repulsive soft dumbbells as a function of size ratio of the two components and their relative degree of deformability. We find a plethora of different phases, which includes most of the mesophases observed in self-assembly of block copolymers but also crystalline structures formed by asymmetric, hard binary mixtures. Our results detail the phenomenological behavior of these systems when softness is introduced in terms of two different classes of interparticle interactions: (a) the elastic Hertz potential, which has a finite energy cost for complete overlap of any two components, and (b) a generic power-law repulsion with tunable exponent. We discuss how simple geometric arguments can be used to account for the large structural variety observed in these systems and detail the similarities and differences in the phase behavior for the two classes of potentials under consideration.

  5. Asymmetric Digital Subscriber Line (ADSL

    Directory of Open Access Journals (Sweden)

    Slavko Šarić

    2012-10-01

    Full Text Available ADSL (Asymmetric Digital Subscriber Line is a technologythat allows transmission at 8.488 Mbps over the existingtelephone copper line (speed range depending on the distance.ADSL circuit connects the ADSL modems by twisted-pairtelephone lines creating three infonnation channels: high speedsimplex (maximum 9 Mbps, medium speed duplex channel(maximum 2 Mbps and plain old telephone service channel.ADSL technology supports up to seven synchronous channelsthat can be configured to meet the needs of the end user.One could simultaneously view four movies stored in MPEG 1fonnat on separate television sets (MPEG 1 transmitted at 1.5Mbps, hold a video-conference (transmitted at 348 kbps,download data files from a server at 128 kbps via ISDN andeven receive a telephone call.

  6. Enantioselective aminocatalysis: Michael addition of unactivated ...

    Indian Academy of Sciences (India)

    KHIANGTE VANLALDINPUIA

    2017-09-25

    Sep 25, 2017 ... D-glucopyranose, galactose and lactose for asymmetric. Michael addition of acetyl acetone to nitro olefins giving up to >99% yield and up to 96% enantiose- lectivity.37 Benaglia et al.,38 used another new class of glucosamine-based bifunctional organocatalysts for nucleophilic Michael addition of ...

  7. Catalytic tar removal from biomass producer gas with secondary air

    Energy Technology Data Exchange (ETDEWEB)

    Lammers, G.; Beenackers, A.A.C.M. [University of Groningen (Netherlands). Dept. of Chemical Engineering; Corella, J. [Universidad Complutense, Madrid (Spain)

    1997-12-31

    The effect of air addition on biomass tar conversion in catalytic packed bed crackers was studied using both an isothermal micro reactor and a fluidised bed bench scale biomass gasification set up with down stream tar crackers. The micro reactor was applied for experiments with artificial biomass producer gas containing naphthalene as a model tar compound. Experiments were carried out with inert silica and catalytically active calcined dolomite bed material both with and without air addition. Experimental results with real tar from the fluidised bed bench scale gasification set up were in qualitative agreement with results from the micro reactor experiments. (author)

  8. Arabinose-derived ketones as catalysts for asymmetric epoxidation of alkenes.

    Science.gov (United States)

    Shing, Tony K M; Leung, Gulice Y C; Luk, To

    2005-09-02

    [reaction: see text] Readily available arabinose-derived ketones, containing a tunable butane-2,3-diacetal as the steric blocker, displayed increasing enantioselectivity (up to 90% ee) with the size of the acetal alkyl group in catalytic asymmetric epoxidation of trans-disubstituted and trisubstituted alkenes. The stereochemical communication between our ketone catalysts and the alkene substrates is mainly due to steric effect, and electronic effect involving pi-pi interaction between phenyl groups of substrate and of catalyst did not appear to be operative in our system.

  9. Asymmetric hydrogenation of ketones: Tactics to achieve high reactivity, enantioselectivity, and wide scope

    Science.gov (United States)

    Ohkuma, Takeshi

    2010-01-01

    Ru complexes with chiral diphosphines and amine-based ligands achieve high catalytic activity and enantioselectivity for the hydrogenation of ketones under neutral to slightly basic conditions. The chiral environment is controllable by changing the combination of these two ligands. A concerted six-membered transition state is proposed to be the origin of the high reactivity. The η6-arene/TsDPEN–Ru and MsDPEN–Cp*Ir catalysts effect the asymmetric reaction under slightly acidic conditions. A variety of chiral secondary alcohols are obtained in high enantiomeric excess. PMID:20228621

  10. Detecting communities by asymmetric intimacy in directed-weighted network

    Science.gov (United States)

    Wang, Xingyuan; Qin, Xiaomeng

    Community detection and analysis have attracted wide public concerns over the recent years. Meanwhile, many related algorithms in complex networks have been proposed. However, most of them concentrate on undirected and unweighted networks. Concerning the significant theoretical value and potential application foreground for directed-weighted networks, in this paper, a novel hierarchical communities detection algorithm (termed as DCBAI) has been proposed on the basis of asymmetric intimacy between nodes. Community structures are effectively detected by node clustering algorithm in directed-weighted network, and a set of optimal communities are generated. In addition, a new and asymmetric parameter is adopted to measure the intimate relationship between nodes. We make some simulation using the proposed algorithm in real-world networks and artificial networks, and the result obtained proves that the parameter can describe the direct and indirect relationships between two nodes. Eventually, comparison with similar algorithms shows that our proposed algorithm has better performance.

  11. Asymmetric Hardware Distortions in Receive Diversity Systems: Outage Performance Analysis

    KAUST Repository

    Javed, Sidrah

    2017-02-22

    This paper studies the impact of asymmetric hardware distortion (HWD) on the performance of receive diversity systems using linear and switched combining receivers. The asymmetric attribute of the proposed model motivates the employment of improper Gaussian signaling (IGS) scheme rather than the traditional proper Gaussian signaling (PGS) scheme. The achievable rate performance is analyzed for the ideal and non-ideal hardware scenarios using PGS and IGS transmission schemes for different combining receivers. In addition, the IGS statistical characteristics are optimized to maximize the achievable rate performance. Moreover, the outage probability performance of the receive diversity systems is analyzed yielding closed form expressions for both PGS and IGS based transmission schemes. HWD systems that employ IGS is proven to efficiently combat the self interference caused by the HWD. Furthermore, the obtained analytic expressions are validated through Monte-Carlo simulations. Eventually, non-ideal hardware transceivers degradation and IGS scheme acquired compensation are quantified through suitable numerical results.

  12. Impact of wind power plant reactive current injection during asymmetrical grid faults

    DEFF Research Database (Denmark)

    Göksu, Ömer; Teodorescu, Remus; Bak, Claus Leth

    2013-01-01

    ) are requested to stay connected and inject positive-sequence reactive current in order to boost positive-sequence grid voltage during short-circuit grid faults, irrespective of the fault type; symmetrical or asymmetrical. However, as shown in this study, when WPPs inject pure positive-sequence reactive current...... in case of asymmetrical faults, as a conventional method (CM) in accordance with the grid code requirement, positive-sequence grid voltage is boosted, but also higher negative sequence voltage in the grid and higher overvoltages at the non-faulty phases occur. In this study, an alternative injection...... method, where WTs are injecting both positive and negative sequence currents during asymmetrical faults, providing improved grid support, is given and compared with the CM. In addition, effect of coupling between positive, negative and zero sequences when WPPs are injecting currents during asymmetrical...

  13. Magmatism, Hydrothermal Cooling and Asymmetric Accretion at Slow-spreading Ridges

    Science.gov (United States)

    Bai, H.; Montesi, L.

    2014-12-01

    Mid-Atlantic Ridge that hydrothermal activities are closely associated with asymmetric segments. In addition, Lavier and Buck [2002] showed that efficient cooling of the lithosphere favors the development of large offset detachments and therefore asymmetric spreading.

  14. Kinetics and mechanism of vanadium catalysed asymmetric cyanohydrin synthesis in propylene carbonate.

    Science.gov (United States)

    North, Michael; Omedes-Pujol, Marta

    2010-11-03

    Propylene carbonate can be used as a green solvent for the asymmetric synthesis of cyanohydrin trimethylsilyl ethers from aldehydes and trimethylsilyl cyanide catalysed by VO(salen)NCS, though reactions are slower in this solvent than the corresponding reactions carried out in dichloromethane. A mechanistic study has been undertaken, comparing the catalytic activity of VO(salen)NCS in propylene carbonate and dichloromethane. Reactions in both solvents obey overall second-order kinetics, the rate of reaction being dependent on the concentration of both the aldehyde and trimethylsilyl cyanide. The order with respect to VO(salen)NCS was determined and found to decrease from 1.2 in dichloromethane to 1.0 in propylene carbonate, indicating that in propylene carbonate, VO(salen)NCS is present only as a mononuclear species, whereas in dichloromethane dinuclear species are present which have previously been shown to be responsible for most of the catalytic activity. Evidence from ⁵¹V NMR spectroscopy suggested that propylene carbonate coordinates to VO(salen)NCS, blocking the free coordination site, thus inhibiting its Lewis acidity and accounting for the reduction in catalytic activity. This explanation was further supported by a Hammett analysis study, which indicated that Lewis base catalysis made a much greater contribution to the overall catalytic activity of VO(salen)NCS in propylene carbonate than in dichloromethane.

  15. Catalytic Three-Component Machinery: Control of Catalytic Activity by Machine Speed.

    Science.gov (United States)

    Paul, Indrajit; Goswami, Abir; Mittal, Nikita; Schmittel, Michael

    2018-01-02

    Three supramolecular slider-on-deck systems DS1-DS3 were obtained as two-component aggregates from the sliders S1-S3 and deck D with its three zinc porphyrin (ZnPor) binding sites. The binding of the two-footed slider to the deck varies with the donor qualities of and the steric hindrance at the pyridine/pyrimidine (pyr) feet, and was effected by two N pyr →ZnPor interactions. Accordingly, the sliders move over the three zinc porphyrins in the deck at different speeds, namely with 32.2, 220, and 440 kHz at room temperature. The addition of N-methylpyrrolidine as an organocatalyst to DS1-DS3 generates catalytic three-component machineries. By using a conjugate addition as a probe reaction, we observed a correlation between the operating speed of the slider-on-deck systems and the yields of the catalytic reaction. As the thermodynamic binding of the slider decreases, both the frequency of the sliding motion and the yield of the catalytic reaction increase. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Modeling of asymmetrical boost converters

    Directory of Open Access Journals (Sweden)

    Eliana Isabel Arango Zuluaga

    2014-01-01

    Full Text Available The asymmetrical interleaved dual boost (AIDB is a fifth-order DC/DC converter designed to interface photovoltaic (PV panels. The AIDB produces small current harmonics to the PV panels, reducing the power losses caused by the converter operation. Moreover, the AIDB provides a large voltage conversion ratio, which is required to step-up the PV voltage to the large dc-link voltage used in grid-connected inverters. To reject irradiance and load disturbances, the AIDB must be operated in a closed-loop and a dynamic model is required. Given that the AIDB converter operates in Discontinuous Conduction Mode (DCM, classical modeling approaches based on Continuous Conduction Mode (CCM are not valid. Moreover, classical DCM modeling techniques are not suitable for the AIDB converter. Therefore, this paper develops a novel mathematical model for the AIDB converter, which is suitable for control-pur-poses. The proposed model is based on the calculation of a diode current that is typically disregarded. Moreover, because the traditional correction to the second duty cycle reported in literature is not effective, a new equation is designed. The model accuracy is contrasted with circuital simulations in time and frequency domains, obtaining satisfactory results. Finally, the usefulness of the model in control applications is illustrated with an application example.

  17. Catalytic Asymmetric Synthesis of 8-Oxabicyclooctanes by Intermolecular [5+2] Pyrylium Cycloadditions**

    Science.gov (United States)

    Witten, Michael R.

    2014-01-01

    Highly enantioselective intermolecular [5+2] cycloadditions of pyrylium ion intermediates with electron-rich alkenes are promoted by a dual catalyst system composed of an achiral thiourea and a chiral primary aminothiourea. The observed enantioselectivity is highly dependent on the substitution pattern of the 5π component, and the basis for this effect is analyzed using experimental and computational evidence. The resultant 8-oxabicyclo[3.2.1]octane derivatives possess a scaffold common in natural products and medicinally active compounds and are also versatile chiral building blocks for further manipulations. Several stereoselective complexity-generating transformations of the 8-oxabicyclooctane products are presented. PMID:24782332

  18. Primary amine/CSA ion pair: A powerful catalytic system for the asymmetric enamine catalysis

    KAUST Repository

    Liu, Chen

    2011-05-20

    A novel ion pair catalyst containing a chiral counteranion can be readily derived by simply mixing cinchona alkaloid-derived diamine with chiral camphorsulfonic acid (CSA). A mixture of 9-amino(9-deoxy)epi-quinine 8 and (-)-CSA was found to be the best catalyst with matching chirality, enabling the direct amination of α-branched aldehydes to proceed in quantitative yields and with nearly perfect enantioselectivities. A 0.5 mol % catalyst loading was sufficient to catalyze the reaction, and a gram scale enantioselective synthesis of biologically important α-methyl phenylglycine has been successfully demonstrated. © 2011 American Chemical Society.

  19. Catalytic Asymmetric C–H Insertions of Rhodium(II) Azavinyl Carbenes

    OpenAIRE

    Chuprakov, Stepan; Malik, Jamal A.; Zibinsky, Mikhail; Fokin, Valery V.

    2011-01-01

    A highly efficient enantioselective C–H insertion of azavinyl carbenes into unactivated alkanes has been developed. These transition metal carbenes are directly generated from readily available and stable 1-sulfonyl-1,2,3-triazoles in the presence of chiral Rh(II) carboxylates and are used for C–H functionalization of alkanes to access a variety of β-chiral sulfonamides.

  20. Catalytic Asymmetric Ring-Opening Reactions of Aziridines with 3-Aryl-Oxindoles.

    Science.gov (United States)

    Wang, Linqing; Li, Dan; Yang, Dongxu; Wang, Kezhou; Wang, Jie; Wang, Pengxin; Su, Wu; Wang, Rui

    2016-03-04

    A highly enantioselective ring-opening alkylation reaction between 3-aryl-oxindole and N-(2-picolinoyl) aziridine has been realized for the first time. The reaction is efficiently mediated by a simple in-situ-generated magnesium catalyst and 3,3'-fluorinated-BINOL (BINOL=1,1'-binaphthalene-2,2'-diol) has been identified as a powerful chiral ligand. Notably, the fluorine atom on the chiral ligand plays a key role in providing the desired chiral 3-alkyl-3-aryl oxindoles with excellent enantioselectivities. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Synthesis of Chiral Tertiary Boronic Esters: Phosphonate-Directed Catalytic Asymmetric Hydroboration of Trisubstituted Alkenes.

    Science.gov (United States)

    Chakrabarty, Suman; Takacs, James M

    2017-05-03

    Highly enantioselective rhodium-catalyzed hydroboration of allylic phosphonates by pinacolborane affords chiral tertiary boronic esters. The β-borylated phosphonates are readily converted to chiral β- and γ-hydroxyphosphonates and aminophosphonates and to phosphonates bearing a quaternary carbon stereocenter. The utility of the latter is illustrated by the synthesis of (S)-(+)-bakuchiol methyl ether.

  2. Catalytic asymmetric mannich-type reaction of N-alkylidene-α-aminoacetonitrile with ketimines.

    Science.gov (United States)

    Lin, Shaoquan; Kawato, Yuji; Kumagai, Naoya; Shibasaki, Masakatsu

    2015-04-20

    Optically active vicinal diamines are versatile chiral building blocks in organic synthesis. A soft Lewis acid/hard Brønsted base cooperative catalyst allows for an efficient stereoselective coupling of N-alkylidene-α-aminoacetonitrile and ketimines to access this class of compounds bearing consecutive tetra- and trisubstituted stereogenic centers. The strategic use of a soft Lewis basic thiophosphinoyl group for ketimines is the key to promoting the reaction, and aliphatic ketimines serve as suitable substrates with as little as 3 mol % catalyst loading. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Congenital asymmetric crying face: a case report

    Directory of Open Access Journals (Sweden)

    Semra Kara

    2011-12-01

    Full Text Available Congenital asymmetric crying face is an anomalia caused by unilateral absence or weakness of depressor anguli oris muscle The major finding of the disease is the absence or weakness in the outer and lower movement of the commissure during crying. The other expression muscles are normal and the face is symmetric at rest. The asymmetry in congenital asymmetric crying face is most evident during infancy but decreases by age. Congenital asymmetric crying face can be associated with cervicofacial, musclebone, respiratory, genitourinary and central nervous system anomalia. It is diagnosed by physical examination. This paper presents a six days old infant with Congenital asymmetric crying face and discusses the case in terms of diagnosis and disease features.

  4. Synthesis of asymmetrical multiantennary human milk oligosaccharides

    NARCIS (Netherlands)

    Prudden, Anthony R; Liu, Lin; Capicciotti, Chantelle J.; Wolfert, Margreet A; Wang, Shuo; Gao, Zhongwei; Meng, Lu; Moremen, Kelley W; Boons, Geert-Jan

    2017-01-01

    Despite mammalian glycans typically having highly complex asymmetrical multiantennary architectures, chemical and chemoenzymatic synthesis has almost exclusively focused on the preparation of simpler symmetrical structures. This deficiency hampers investigations into the biology of glycan-binding

  5. Asymmetric cryptography based on wavefront sensing.

    Science.gov (United States)

    Peng, Xiang; Wei, Hengzheng; Zhang, Peng

    2006-12-15

    A system of asymmetric cryptography based on wavefront sensing (ACWS) is proposed for the first time to our knowledge. One of the most significant features of the asymmetric cryptography is that a trapdoor one-way function is required and constructed by analogy to wavefront sensing, in which the public key may be derived from optical parameters, such as the wavelength or the focal length, while the private key may be obtained from a kind of regular point array. The ciphertext is generated by the encoded wavefront and represented with an irregular array. In such an ACWS system, the encryption key is not identical to the decryption key, which is another important feature of an asymmetric cryptographic system. The processes of asymmetric encryption and decryption are formulized mathematically and demonstrated with a set of numerical experiments.

  6. Stereogenic-Only-at-Metal Asymmetric Catalysts.

    Science.gov (United States)

    Zhang, Lilu; Meggers, Eric

    2017-09-19

    Chirality is an essential feature of asymmetric catalysts. This review summarizes asymmetric catalysts that derive their chirality exclusively from stereogenic metal centers. Reported chiral-at-metal catalysts can be divided into two classes, namely, inert metal complexes, in which the metal fulfills a purely structural role, so catalysis is mediated entirely through the ligand sphere, and reactive metal complexes. The latter are particularly appealing because structural simplicity (only achiral ligands) is combined with the prospect of particularly effective asymmetric induction (direct contact of the substrate with the chiral metal center). Challenges and solutions for the design of such reactive stereogenic-only-at-metal asymmetric catalysts are discussed. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Magnetically Modified Asymmetric Supercapacitors, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — This Small Business Innovation Research Phase I project is for the development of an asymmetric supercapacitor that will have improved energy density and cycle life....

  8. High-Voltage, Asymmetric-Waveform Generator

    Science.gov (United States)

    Beegle, Luther W.; Duong, Tuan A.; Duong, Vu A.; Kanik, Isik

    2008-01-01

    The shapes of waveforms generated by commercially available analytical separation devices, such as some types of mass spectrometers and differential mobility spectrometers are, in general, inadequate and result in resolution degradation in output spectra. A waveform generator was designed that would be able to circumvent these shortcomings. It is capable of generating an asymmetric waveform, having a peak amplitude as large as 2 kV and frequency of several megahertz, which can be applied to a capacitive load. In the original intended application, the capacitive load would consist of the drift plates in a differential-mobility spectrometer. The main advantage to be gained by developing the proposed generator is that the shape of the waveform is made nearly optimum for various analytical devices requiring asymmetric-waveform such as differential-mobility spectrometers. In addition, this waveform generator could easily be adjusted to modify the waveform in accordance with changed operational requirements for differential-mobility spectrometers. The capacitive nature of the load is an important consideration in the design of the proposed waveform generator. For example, the design provision for shaping the output waveform is based partly on the principle that (1) the potential (V) on a capacitor is given by V=q/C, where C is the capacitance and q is the charge stored in the capacitor; and, hence (2) the rate of increase or decrease of the potential is similarly proportional to the charging or discharging current. The proposed waveform generator would comprise four functional blocks: a sine-wave generator, a buffer, a voltage shifter, and a high-voltage switch (see Figure 1). The sine-wave generator would include a pair of operational amplifiers in a feedback configuration, the parameters of which would be chosen to obtain a sinusoidal timing signal of the desired frequency. The buffer would introduce a slight delay (approximately equal to 20 ns) but would otherwise

  9. Catalytic Decoupling of Quantum Information

    DEFF Research Database (Denmark)

    Majenz, Christian; Berta, Mario; Dupuis, Frédéric

    2017-01-01

    The decoupling technique is a fundamental tool in quantum information theory with applications ranging from quantum thermodynamics to quantum many body physics to the study of black hole radiation. In this work we introduce the notion of catalytic decoupling, that is, decoupling in the presence...... of an uncorrelated ancilla system. This removes a restriction on the standard notion of decoupling, which becomes important for structureless resources, and yields a tight characterization in terms of the max-mutual information. Catalytic decoupling naturally unifies various tasks like the erasure of correlations...

  10. Catalytic activity of Au nanoparticles

    DEFF Research Database (Denmark)

    Larsen, Britt Hvolbæk; Janssens, Ton V.W.; Clausen, Bjerne

    2007-01-01

    Au is usually viewed as an inert metal, but surprisingly it has been found that Au nanoparticles less than 3–5 nm in diameter are catalytically active for several chemical reactions. We discuss the origin of this effect, focusing on the way in which the chemical activity of Au may change with par......Au is usually viewed as an inert metal, but surprisingly it has been found that Au nanoparticles less than 3–5 nm in diameter are catalytically active for several chemical reactions. We discuss the origin of this effect, focusing on the way in which the chemical activity of Au may change...

  11. Engineered Asymmetric Composite Membranes with Rectifying Properties.

    Science.gov (United States)

    Wen, Liping; Xiao, Kai; Sainath, Annadanam V Sesha; Komura, Motonori; Kong, Xiang-Yu; Xie, Ganhua; Zhang, Zhen; Tian, Ye; Iyoda, Tomokazu; Jiang, Lei

    2016-01-27

    Asymmetric composite membranes with rectifying properties are developed by grafting pH-stimulus-responsive materials onto the top layer of the composite structure, which is prepared by two novel block copolymers using a phase-separation technique. This engineered asymmetric composite membrane shows potential applications in sensors, filtration, and nanofluidic devices. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. STUDI TEKNOLOGI ASYMMETRIC DIGITAL SUBSCRIBER LINE

    OpenAIRE

    Syarif, Syafruddin

    2008-01-01

    ADSL is one of the xDSL variants are being developed. ADSL allows high-speed data transmission with asymmetric bandwidth to support the implementation of multimedia services on broadband network using telephone cable network that already exist. Is called asymmetric because bit rate from the downstream (central to the customer) is greater than the upstream direction (customer to central) or it can be said that bit rate of downstream direction is different than the upstream dir...

  13. Studi Teknologi Asymmetric Digital Subcriber Line

    OpenAIRE

    SYAFRUDDIN SYARIF, SYAFRUDDIN SYARIF

    2008-01-01

    - ADSL is one of the xDSL variants are being developed. ADSL allows high-speed data transmission with asymmetric bandwidth to support the implementation of multimedia services on broadband network using telephone cable network that already exist. Is called asymmetric because bit rate from the downstream (central to the customer) is greater than the upstream direction (customer to central) or it can be said that bit rate of downstream direction is different than the upstream direction. Bit ...

  14. Preparation of Mg-doped Ce-Zr Solid Catalysts and Their Catalytic ...

    African Journals Online (AJOL)

    NICO

    Knoevenagel condensation using aromatic aldehydes and 2,4-thiazolidinedione in ethanol:water medium. The best catalytic activity was ... Addition of MgO to the Ce-Zr mixed metal oxides affected both particle size and catalytic activity. KEYWORDS ... piperidine in EtOH,9 NaOAc in DMF-AcOH10, ethylene- diammonium ...

  15. Characteristics of Braced Excavation under Asymmetrical Loads

    Directory of Open Access Journals (Sweden)

    Changjie Xu

    2013-01-01

    Full Text Available Numerous excavation practices have shown that large discrepancies exist between field monitoring data and calculated results when the conventional symmetry-plane method (with half-width is used to design the retaining structure under asymmetrical loads. To examine the characteristics of a retaining structure under asymmetrical loads, we use the finite element method (FEM to simulate the excavation process under four different groups of asymmetrical loads and create an integrated model to tackle this problem. The effects of strut stiffness and wall length are also investigated. The results of numerical analysis clearly imply that the deformation and bending moment of diaphragm walls are distinct on different sides, indicating the need for different rebar arrangements when the excavation is subjected to asymmetrical loads. This study provides a practical approach to designing excavations under asymmetrical loads. We analyze and compare the monitoring and calculation data at different excavation stages and find some general trends. Several guidelines on excavation design under asymmetrical loads are drawn.

  16. All conducting polymer electrodes for asymmetric solid-state supercapacitors

    KAUST Repository

    Kurra, Narendra

    2015-02-16

    In this study, we report the fabrication of solid-state asymmetric supercapacitors (ASCs) based on conducting polymer electrodes on a plastic substrate. Nanostructured conducting polymers of poly(3,4-ethylenedioxythiophene), PEDOT, and polyaniline (PANI) are deposited electrochemically over Au-coated polyethylene naphthalate (PEN) plastic substrates. Due to the electron donating nature of the oxygen groups in the PEDOT, reduction potentials are higher, allowing it to be used as a negative electrode material. In addition, the high stability of PEDOT in its oxidised state makes it capable to exhibit electrochemical activity in a wide potential window. This can qualify PEDOT to be used as a negative electrode in fabricating asymmetric solid state supercapacitors with PANI as a positive electrode while employing polyvinyl alcohol (PVA)/H2SO4 gel electrolyte. The ASCs exhibit a maximum power density of 2.8 W cm−3 at an energy density of 9 mW h cm−3, which is superior to the carbonaceous and metal oxide based ASC solid state devices. Furthermore, the tandem configuration of asymmetric supercapacitors is shown to be capable of powering a red light emitting diode for about 1 minute after charging for 10 seconds.

  17. Seismic Response of Plan-Asymmetric Structures with Diaphragm Flexibility

    Directory of Open Access Journals (Sweden)

    Hamed Eivani

    2018-01-01

    Full Text Available The seismic behavior of asymmetric structures with a flexible diaphragm was studied by conducting inelastic dynamic time-history analyses. Asymmetric structures with different configurations of mass, stiffness, and strength centers, in combination with a wide range of diaphragm flexibility, were evaluated. The behavior of structures was studied by considering three aspects: (1 effect of structural asymmetry on diaphragms deformation; (2 effect of diaphragm flexibility on demands of the lateral load-resisting elements; (3 optimum configuration of mass, stiffness, and strength centers to limit important engineering demand parameters in asymmetric structures with a flexible diaphragm. The results showed that the shear-dominant deformation of diaphragms is sensitive to both structure asymmetry specifications and the degree of diaphragm flexibility; therefore, it can be used for the qualitative classification of the seismic behavior of structures. Also, the center of strength in structures with flexible diaphragm is more important relative to the stiffness center and has a significant effect on engineering demands at all levels of diaphragm flexibility. Moreover, it was found that a suitable configuration of centers in torsionally stiff structures depends on the degree of diaphragm flexibility, in addition to the intensity of earthquakes (structure yield level and selected engineering demand parameter.

  18. Theoretical insights into catalytic mechanism of protein arginine methyltransferase 1.

    Directory of Open Access Journals (Sweden)

    Ruihan Zhang

    Full Text Available Protein arginine methyltransferase 1 (PRMT1, the major arginine asymmetric dimethylation enzyme in mammals, is emerging as a potential drug target for cancer and cardiovascular disease. Understanding the catalytic mechanism of PRMT1 will facilitate inhibitor design. However, detailed mechanisms of the methyl transfer process and substrate deprotonation of PRMT1 remain unclear. In this study, we present a theoretical study on PRMT1 catalyzed arginine dimethylation by employing molecular dynamics (MD simulation and quantum mechanics/molecular mechanics (QM/MM calculation. Ternary complex models, composed of PRMT1, peptide substrate, and S-adenosyl-methionine (AdoMet as cofactor, were constructed and verified by 30-ns MD simulation. The snapshots selected from the MD trajectory were applied for the QM/MM calculation. The typical SN2-favored transition states of the first and second methyl transfers were identified from the potential energy profile. Deprotonation of substrate arginine occurs immediately after methyl transfer, and the carboxylate group of E144 acts as proton acceptor. Furthermore, natural bond orbital analysis and electrostatic potential calculation showed that E144 facilitates the charge redistribution during the reaction and reduces the energy barrier. In this study, we propose the detailed mechanism of PRMT1-catalyzed asymmetric dimethylation, which increases insight on the small-molecule effectors design, and enables further investigations into the physiological function of this family.

  19. Food additives

    Science.gov (United States)

    ... this page: //medlineplus.gov/ency/article/002435.htm Food additives To use the sharing features on this page, please enable JavaScript. Food additives are substances that become part of a food ...

  20. Asymmetric Bessel-Gauss beams.

    Science.gov (United States)

    Kotlyar, V V; Kovalev, A A; Skidanov, R V; Soifer, V A

    2014-09-01

    We propose a three-parameter family of asymmetric Bessel-Gauss (aBG) beams with integer and fractional orbital angular momentum (OAM). The aBG beams are described by the product of a Gaussian function by the nth-order Bessel function of the first kind of complex argument, having finite energy. The aBG beam's asymmetry degree depends on a real parameter c≥0: at c=0, the aBG beam is coincident with a conventional radially symmetric Bessel-Gauss (BG) beam; with increasing c, the aBG beam acquires a semicrescent shape, then becoming elongated along the y axis and shifting along the x axis for c≫1. In the initial plane, the intensity distribution of the aBG beams has a countable number of isolated optical nulls on the x axis, which result in optical vortices with unit topological charge and opposite signs on the different sides of the origin. As the aBG beam propagates, the vortex centers undergo a nonuniform rotation with the entire beam about the optical axis (c≫1), making a π/4 turn at the Rayleigh range and another π/4 turn after traveling the remaining distance. At different values of the c parameter, the optical nulls of the transverse intensity distribution change their position, thus changing the OAM that the beam carries. An isolated optical null on the optical axis generates an optical vortex with topological charge n. A vortex laser beam shaped as a rotating semicrescent has been generated using a spatial light modulator.

  1. Hydrogen-Bond Directed Regioselective Pd-Catalyzed Asymmetric Allylic Alkylation: The Construction of Chiral α-Amino Acids with Vicinal Tertiary and Quaternary Stereocenters.

    Science.gov (United States)

    Wei, Xuan; Liu, Delong; An, Qianjin; Zhang, Wanbin

    2015-12-04

    A Pd-catalyzed asymmetric allylic alkylation of azlactones with 4-arylvinyl-1,3-dioxolan-2-ones was developed, providing "branched" chiral α-amino acids with vicinal tertiary and quaternary stereocenters, in high yields and with excellent selectivities. Mechanistic studies revealed that the formation of a hydrogen bond between the Pd-allylic complex and azlactone isomer is responsible for the excellent regioselectivities. This asymmetric alkylation can be carried out on a gram scale without a loss of catalytic efficiency, and the resulting product can be further transformed to a chiral azetidine in two simple steps.

  2. Engineering reactors for catalytic reactions

    Indian Academy of Sciences (India)

    ... improvements in reactor performance. In this article, application of recent (and not so recent) developments in engineering reactors for catalytic reactions is discussed. Some examples where performance enhancement was realized by catalyst design, appropriate choice of reactor, better injection and dispersion strategies ...

  3. Catalytic properties of niobium compounds

    International Nuclear Information System (INIS)

    Tanabe, K.; Iizuka, T.

    1983-04-01

    The catalytic activity and selectivity of niobium compounds including oxides, salts, organometallic compounds and others are outlined. The application of these compounds as catalysts to diversified reactions is reported. The nature and action of niobium catalysts are characteristic and sometimes anomalous, suggesting the necessity of basic research and the potential use as catalysts for important processes in the chemical industry. (Author) [pt

  4. Catalytic carboxyester hydrolysis by diaminodiphenols

    Indian Academy of Sciences (India)

    Administrator

    Two diaminodiphenols, 1 and 2, have been examined as catalysts for the hydrolysis of 4- nitrophenyl acetate (NA) and 4-nitrophenylphosphate (NP) in aqueous-acetonitrile (25% acetonitrile v/v) media at 35ºC, I = 1·0 mol dm–3. The compound 1 enhances the hydrolysis rate of NA more than 105 times. Its catalytic efficiency ...

  5. Engineering reactors for catalytic reactions

    Indian Academy of Sciences (India)

    on selectivity can make substantial impact on process viability and economics. Extensive studies have been conducted to establish sound basis for design and engineering of reactors for practising such catalytic reactions and for realizing improvements in reactor performance. In this article, application of recent (and not so ...

  6. Catalytic aspects of a copper (II) complex: biological oxidase to ...

    Indian Academy of Sciences (India)

    This copper complex displays excellent catalytic efficiency, kcat /KM (h⁻¹) = 6.17 × 10⁵ towards the oxidative coupling of 2-aminophenol (2-AP) to aminophenoxazin-3-one. Further, upon stoichiometric addition of copper(II) complex to 3,5-DTBC in presence of molecular oxygen in ethanol medium, the copper complex ...

  7. Asymmetric statistical features of the Chinese domestic and international gold price fluctuation

    Science.gov (United States)

    Cao, Guangxi; Zhao, Yingchao; Han, Yan

    2015-05-01

    Analyzing the statistical features of fluctuation is remarkably significant for financial risk identification and measurement. In this study, the asymmetric detrended fluctuation analysis (A-DFA) method was applied to evaluate asymmetric multifractal scaling behaviors in the Shanghai and New York gold markets. Our findings showed that the multifractal features of the Chinese and international gold spot markets were asymmetric. The gold return series persisted longer in an increasing trend than in a decreasing trend. Moreover, the asymmetric degree of multifractals in the Chinese and international gold markets decreased with the increase in fluctuation range. In addition, the empirical analysis using sliding window technology indicated that multifractal asymmetry in the Chinese and international gold markets was characterized by its time-varying feature. However, the Shanghai and international gold markets basically shared a similar asymmetric degree evolution pattern. The American subprime mortgage crisis (2008) and the European debt crisis (2010) enhanced the asymmetric degree of the multifractal features of the Chinese and international gold markets. Furthermore, we also make statistical tests for the results of multifractatity and asymmetry, and discuss the origin of them. Finally, results of the empirical analysis using the threshold autoregressive conditional heteroskedasticity (TARCH) and exponential generalized autoregressive conditional heteroskedasticity (EGARCH) models exhibited that good news had a more significant effect on the cyclical fluctuation of the gold market than bad news. Moreover, good news exerted a more significant effect on the Chinese gold market than on the international gold market.

  8. Daam1a mediates asymmetric habenular morphogenesis by regulating dendritic and axonal outgrowth

    Science.gov (United States)

    Colombo, Alicia; Palma, Karina; Armijo, Lorena; Mione, Marina; Signore, Iskra A.; Morales, Camila; Guerrero, Néstor; Meynard, Margarita M.; Pérez, Ramón; Suazo, José; Marcelain, Katherine; Briones, Luis; Härtel, Steffen; Wilson, Stephen W.; Concha, Miguel L.

    2013-01-01

    Although progress has been made in resolving the genetic pathways that specify neuronal asymmetries in the brain, little is known about genes that mediate the development of structural asymmetries between neurons on left and right. In this study, we identify daam1a as an asymmetric component of the signalling pathways leading to asymmetric morphogenesis of the habenulae in zebrafish. Daam1a is a member of the Formin family of actin-binding proteins and the extent of Daam1a expression in habenular neuron dendrites mirrors the asymmetric growth of habenular neuropil between left and right. Local loss and gain of Daam1a function affects neither cell number nor subtype organisation but leads to a decrease or increase of neuropil, respectively. Daam1a therefore plays a key role in the asymmetric growth of habenular neuropil downstream of the pathways that specify asymmetric cellular domains in the habenulae. In addition, Daam1a mediates the development of habenular efferent connectivity as local loss and gain of Daam1a function impairs or enhances, respectively, the growth of habenular neuron terminals in the interpeduncular nucleus. Abrogation of Daam1a disrupts the growth of both dendritic and axonal processes and results in disorganised filamentous actin and α-tubulin. Our results indicate that Daam1a plays a key role in asymmetric habenular morphogenesis mediating the growth of dendritic and axonal processes in dorsal habenular neurons. PMID:24046318

  9. DEVELOPMENT OF HIGH ACTIVITY, CATALYTIC SYSTEMS FOR NOx REDUCTION

    Energy Technology Data Exchange (ETDEWEB)

    Unknown

    2001-12-01

    This project was directed at an investigation of catalytic NO{sub x} reduction on carbonaceous supports at low temperatures. The experimental work was conducted primarily in a packed bed reactor/gas flow system that was constructed for this work. The analytical techniques employed were mass spectrometry, NO{sub x} chemiluminescence, and gas chromatography. The experimental plan was focused on steady-state reactivity experiments, followed by temperature programmed desorption (TPD) of surface intermediates, and also selected temperature-programmed reaction (TPR) experiments. Both uncatalyzed and catalyzed (potassium-promoted) phenolic resin char, were investigated as well as the catalytic effect of additional CO in the gas phase.

  10. Hydrophilic Pt nanoflowers: synthesis, crystallographic analysis and catalytic performance.

    Science.gov (United States)

    Mourdikoudis, Stefanos; Altantzis, Thomas; Liz-Marzán, Luis M; Bals, Sara; Pastoriza-Santos, Isabel; Pérez-Juste, Jorge

    2016-05-21

    Water-soluble Pt nanoflowers (NFs) were prepared by diethylene glycol-mediated reduction of Pt acetylacetonate (Pt(acac) 2 ) in the presence of polyethylenimine. Advanced electron microscopy analysis showed that the NFs consist of multiple branches with a truncated cubic morphology and different crystallographic orientations. We demonstrate that the nature of the solvent strongly influences the resulting morphology. The catalytic performance of the Pt NFs in 4-nitrophenol reduction was found to be superior to that of other nanoparticle-based catalysts. Additionally, the Pt NFs display good catalytic reusability with no loss of activity after five consecutive cycles.

  11. Inclined asymmetric librations in exterior resonances

    Science.gov (United States)

    Voyatzis, G.; Tsiganis, K.; Antoniadou, K. I.

    2018-04-01

    Librational motion in Celestial Mechanics is generally associated with the existence of stable resonant configurations and signified by the existence of stable periodic solutions and oscillation of critical (resonant) angles. When such an oscillation takes place around a value different than 0 or π , the libration is called asymmetric. In the context of the planar circular restricted three-body problem, asymmetric librations have been identified for the exterior mean motion resonances (MMRs) 1:2, 1:3, etc., as well as for co-orbital motion (1:1). In exterior MMRs the massless body is the outer one. In this paper, we study asymmetric librations in the three-dimensional space. We employ the computational approach of Markellos (Mon Not R Astron Soc 184:273-281, https://doi.org/10.1093/mnras/184.2.273, 1978) and compute families of asymmetric periodic orbits and their stability. Stable asymmetric periodic orbits are surrounded in phase space by domains of initial conditions which correspond to stable evolution and librating resonant angles. Our computations were focused on the spatial circular restricted three-body model of the Sun-Neptune-TNO system (TNO = trans-Neptunian object). We compare our results with numerical integrations of observed TNOs, which reveal that some of them perform 1:2 resonant, inclined asymmetric librations. For the stable 1:2 TNO librators, we find that their libration seems to be related to the vertically stable planar asymmetric orbits of our model, rather than the three-dimensional ones found in the present study.

  12. Catalytic Promiscuity of Ancestral Esterases and Hydroxynitrile Lyases.

    Science.gov (United States)

    Devamani, Titu; Rauwerdink, Alissa M; Lunzer, Mark; Jones, Bryan J; Mooney, Joanna L; Tan, Maxilmilien Alaric O; Zhang, Zhi-Jun; Xu, Jian-He; Dean, Antony M; Kazlauskas, Romas J

    2016-01-27

    Catalytic promiscuity is a useful, but accidental, enzyme property, so finding catalytically promiscuous enzymes in nature is inefficient. Some ancestral enzymes were branch points in the evolution of new enzymes and are hypothesized to have been promiscuous. To test the hypothesis that ancestral enzymes were more promiscuous than their modern descendants, we reconstructed ancestral enzymes at four branch points in the divergence hydroxynitrile lyases (HNL's) from esterases ∼ 100 million years ago. Both enzyme types are α/β-hydrolase-fold enzymes and have the same catalytic triad, but differ in reaction type and mechanism. Esterases catalyze hydrolysis via an acyl enzyme intermediate, while lyases catalyze an elimination without an intermediate. Screening ancestral enzymes and their modern descendants with six esterase substrates and six lyase substrates found higher catalytic promiscuity among the ancestral enzymes (P promiscuous and catalyzed both hydrolysis and lyase reactions with many substrates. A broader screen tested mechanistically related reactions that were not selected for by evolution: decarboxylation, Michael addition, γ-lactam hydrolysis and 1,5-diketone hydrolysis. The ancestral enzymes were more promiscuous than their modern descendants (P = 0.04). Thus, these reconstructed ancestral enzymes are catalytically promiscuous, but HNL1 is especially so.

  13. Catalytic partial oxidation of methanol and ethanol for hydrogen generation.

    Science.gov (United States)

    Hohn, Keith L; Lin, Yu-Chuan

    2009-01-01

    Hydrogen-powered fuel cell vehicles feature high energy efficiency and minor environmental impact. Liquid fuels are ideal hydrogen carriers, which can catalytically be converted into syngas or hydrogen to power vehicles. Among the potential liquid fuels, alcohols have several advantages. The hydrogen/carbon ratio is higher than that of other liquid hydrocarbons or oxygenates, especially in the case of methanol. In addition, alcohols can be derived from renewable biomass resources. Catalytic partial oxidation of methanol or ethanol offers immense potential for onboard hydrogen generation due to its rapid reaction rate and exothermic nature. These benefits stimulate a burgeoning research community in catalyst design, reaction engineering, and mechanistic investigation. The purpose of this Minireview is to provide insight into syngas and hydrogen production from methanol and ethanol partial oxidation, particularly highlighting catalytic chemistry.

  14. Techno-economic assessment of catalytic gasification of biomass powders for methanol production.

    Science.gov (United States)

    Carvalho, Lara; Furusjö, Erik; Kirtania, Kawnish; Wetterlund, Elisabeth; Lundgren, Joakim; Anheden, Marie; Wolf, Jens

    2017-08-01

    This study evaluated the techno-economic performance and potential benefits of methanol production through catalytic gasification of forest residues and lignin. The results showed that while catalytic gasification enables increased cold gas efficiencies and methanol yields compared to non-catalytic gasification, the additional pre-treatment energy and loss of electricity production result in small or no system efficiency improvements. The resulting required methanol selling prices (90-130€/MWh) are comparable with production costs for other biofuels. It is concluded that catalytic gasification of forest residues can be an attractive option as it provides operational advantages at production costs comparable to non-catalytic gasification. The addition of lignin would require lignin costs below 25€/MWh to be economically beneficial. Copyright © 2017 Elsevier Ltd. All rights reserved.

  15. Asymmetric biocatalysis with microbial enzymes and cells.

    Science.gov (United States)

    Wohlgemuth, Roland

    2010-06-01

    Microbial enzymes and cells continue to be important tools and nature's privileged chiral catalysts for performing asymmetric biocatalysis from the analytical small scale to the preparative and large scale in synthesis and degradation. The application of biocatalysts for preparing molecular asymmetry has achieved high efficiency, enantioselectivity and yield and is experiencing today a worldwide renaissance. Recent developments in the discovery, development and production of stable biocatalysts, in the design of new biocatalytic processes and in the product recovery and purification processes have made biocatalytic approaches using microbial cells and enzymes attractive choices for the synthesis of chiral compounds. The methodologies of kinetic resolution and kinetic asymmetric transformation, dynamic kinetic resolution and deracemization, desymmetrization, asymmetric synthesis with or without diastereo control and multi-step asymmetric biocatalysis are finding increasing applications in research. The ever-increasing use of hydrolytic enzymes has been accompanied by new applications of oxidoreductases, transferases and lyases. Isomerases, already used in large-scale processes, and ligases, are emerging as interesting biocatalysts for new synthetic applications. The production of a wide variety of industrial products by asymmetric biocatalysis has even become the preferred method of production. Copyright 2010 Elsevier Ltd. All rights reserved.

  16. Additive manufacturing.

    Science.gov (United States)

    Mumith, A; Thomas, M; Shah, Z; Coathup, M; Blunn, G

    2018-04-01

    Increasing innovation in rapid prototyping (RP) and additive manufacturing (AM), also known as 3D printing, is bringing about major changes in translational surgical research. This review describes the current position in the use of additive manufacturing in orthopaedic surgery. Cite this article: Bone Joint J 2018;100-B:455-60.

  17. Transmission capability of asymmetric digital subscriber lines in Taiwan

    Science.gov (United States)

    Wei, Shyue-Win; Leu, Shyue-Tzong; Wei, Che-Ho

    1995-04-01

    The transmission capacity of discrete multitone (DMT) modulation system for Taiwan's subscriber loops is evaluated in this study. Based on the characteristics of Taiwan's local loops, the transmission capacity is estimated to be 1.544 Mb/s and 6 Mb/s in Taiwan. Simulation results also show how many percents of users in Taiwan may have 1.544 Mb/s or 6 Mb/s of asymmetric digital subscriber lines (ADSL) services. Self far-end crosstalk (FEXT) and additive white Gaussian noise (AWGN) are considered to be the dominant noise sources in the work.

  18. A DFT based method for calculating the surface energies of asymmetric MoP facets

    Science.gov (United States)

    Tian, Xinxin; Wang, Tao; Fan, Lifang; Wang, Yuekui; Lu, Haigang; Mu, Yuewen

    2018-01-01

    MoP is a promising catalyst in heterogeneous catalysis. Understanding its surface stability and morphology is the first and essential step in exploring its catalytic properties. However, traditional surface energy calculation method does not work for the asymmetric termination of MoP. In this work, we reported a useful DFT based method to get the surface energies of asymmetric MoP facets. Under ideal condition, the (101) surface with mixed Mo/P termination is most stable, followed by the (100) surface, while the (001) surface is least stable. Wulff construction reveals the exposure of six surfaces on the MoP nanoparticle, where the (101) has the largest contribution. Atomistic thermodynamics results reveal the changes in surface stability orders with experimental conditions, and the (001)-P termination becomes more and more stable with increasing P chemical potential, which indicates its exposure is possible at defined conditions. Our results agree well with the previous experimental XRD and TEM data. We believe the reported method for surface energy calculation could be extended to other similar systems with asymmetric surface terminations.

  19. Catalytic enantioselective synthesis of chiral organic compounds of ultra-high purity of >99% ee.

    Science.gov (United States)

    Negishi, Ei-ichi; Xu, Shiqing

    2015-01-01

    Shortly after the discovery of Zr-catalyzed carboalumination of alkynes in 1978, we sought expansion of the scope of this reaction so as to develop its alkene version for catalytic asymmetric C-C bond formation, namely the ZACA (Zr-catalyzed asymmetric carboalumination of alkenes). However, this seemingly easy task proved to be quite challenging. The ZACA reaction was finally discovered in 1995 by suppressing three competitive side reactions, i.e., (i) cyclic carbometalation, (ii) β-H transfer hydrometalation, and (iii) alkene polymerization. The ZACA reaction has been used to significantly modernize and improve syntheses of various natural products including deoxypolypropionates and isoprenoids. This review focuses on our recent progress on the development of ZACA-lipase-catalyzed acetylation-transition metal-catalyzed cross-coupling processes for highly efficient and enantioselective syntheses of a wide range of chiral organic compounds with ultra-high enantiomeric purities.

  20. Vapor Phase Catalytic Ammonia Reduction

    Science.gov (United States)

    Flynn, Michael T.; Harper, Lynn D. (Technical Monitor)

    1994-01-01

    This paper discusses the development of a Vapor Phase Catalytic Ammonia Reduction (VPCAR) teststand and the results of an experimental program designed to evaluate the potential of the technology as a water purification process. In the experimental program the technology is evaluated based upon product water purity, water recovery rate, and power consumption. The experimental work demonstrates that the technology produces high purity product water and attains high water recovery rates at a relatively high specific power consumption. The experimental program was conducted in 3 phases. In phase I an Igepon(TM) soap and water mixture was used to evaluate the performance of an innovative Wiped-Film Rotating-Disk evaporator and associated demister. In phase II a phenol-water solution was used to evaluate the performance of the high temperature catalytic oxidation reactor. In phase III a urine analog was used to evaluate the performance of the combined distillation/oxidation functions of the processor.

  1. Multi-agent Bargaining under Asymmetric Information

    DEFF Research Database (Denmark)

    Asplund, Marcus; Genesove, David

    information aspect is due to partly unobserved individual valuations of an elevator. We tailor Hellwig (2003) to the features of the retrofitting problem and use this to predict which building characteristics should make it easier for owners to agree. Data from Copenhagen broadly support the model......It is well know that asymmetric information might lead to underprovision of public goods. To test the theoretical prediction, we study the decision to retrofit an elevator into an old apartment building, in which each owner has to agree on how the investment cost is split. The asymmetric......'s predictions. We use transaction data to estimate the market value of an elevator and conclude that for approximately 30-40 percent of the buildings without an elevator the aggregate increase in value exceeds the investment cost....

  2. Renewable resource management under asymmetric information

    DEFF Research Database (Denmark)

    Jensen, Frank; Andersen, Peder; Nielsen, Max

    2013-01-01

    Asymmetric information between fishermen and the regulator is important within fisheries. The regulator may have less information about stock sizes, prices, costs, effort, productivity and catches than fishermen. With asymmetric information, a strong analytical tool is principal-agent analysis....... In this paper, we study asymmetric information about productivity within a principal-agent framework and a tax on fishing effort is considered. It is shown that a second best optimum can be achieved if the effort tax is designed such that low-productivity agents rent is exhausted, while high-productivity agents...... receive an information rent. The information rent is equivalent to the total incentive cost. The incentive costs arise as we want to reveal the agent's type....

  3. Asymmetric synthesis II more methods and applications

    CERN Document Server

    Christmann, Mathias

    2012-01-01

    After the overwhelming success of 'Asymmetric Synthesis - The Essentials', narrating the colorful history of asymmetric synthesis, this is the second edition with latest subjects and authors. While the aim of the first edition was mainly to honor the achievements of the pioneers in asymmetric syntheses, the aim of this new edition was bringing the current developments, especially from younger colleagues, to the attention of students. The format of the book remained unchanged, i.e. short conceptual overviews by young leaders in their field including a short biography of the authors. The growing multidisciplinary research within chemistry is reflected in the selection of topics including metal catalysis, organocatalysis, physical organic chemistry, analytical chemistry, and its applications in total synthesis. The prospective reader of this book is a graduate or undergraduate student of advanced organic chemistry as well as the industrial chemist who wants to get a brief update on the current developments in th...

  4. Inorganic membranes and catalytic reactors

    OpenAIRE

    Rangel, Maria do Carmo

    1997-01-01

    Membrane reactors are reviewed with emphasis in their applications in catalysis field. The basic principles of these systems are presented as well as a historical development. The several kinds of catalytic membranes and their preparations are discussed including the problems, needs and challenges to be solved in order to use these reactors in commercial processes. Some applications of inorganic membrane reactors are also shown. It was concluded that these systems have a great potential for i...

  5. Homogeneous asymmetric catalysis in fragrance chemistry.

    Science.gov (United States)

    Ciappa, Alessandra; Bovo, Sara; Bertoldini, Matteo; Scrivanti, Alberto; Matteoli, Ugo

    2008-06-01

    Opposite enantiomers of a chiral fragrance may exhibit different olfactory activities making a synthesis in high enantiomeric purity commercially and scientifically interesting. Accordingly, the asymmetric synthesis of four chiral odorants, Fixolide, Phenoxanol, Citralis, and Citralis Nitrile, has been investigated with the aim to develop practically feasible processes. In the devised synthetic schemes, the key step that leads to the formation of the stereogenic center is the homogeneous asymmetric hydrogenation of a prochiral olefin. By an appropriate choice of the catalyst and the reaction conditions, Phenoxanol, Citralis, and Citralis Nitrile were obtained in high enantiomeric purity, and odor profiles of the single enantiomers were determined.

  6. Asymmetric energy B factory at KEK

    International Nuclear Information System (INIS)

    Watanabe, Yasushi

    1994-01-01

    An introductory review is given on the project of the Asymmetric Energy B factory at KEK. First, the motivation for B factory is discussed. The most interesting and important topic there is the measurement of CP violation in other than the K-system. Thus, CP violation in the B decays is reviewed rather extensively, especially on how the angles of the unitarity triangle can be measured at an asymmetric energy B factory. Then the B factory project at KEK is briefly reviewed. (author)

  7. Crystallization and preliminary crystallographic studies of the Pasteurella multocida toxin catalytic domain

    Energy Technology Data Exchange (ETDEWEB)

    Miyazawa, Masayuki [Research Institute for Microbial Diseases, Osaka University, 3-1 Yamada-oka, Suita-shi, Osaka 565-0871 (Japan); Kitadokoro, Kengo [Research Center for Low Temperature and Materials Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan); Kamitani, Shigeki; Shime, Hiroaki; Horiguchi, Yasuhiko, E-mail: horiguti@biken.osaka-u.ac.jp [Research Institute for Microbial Diseases, Osaka University, 3-1 Yamada-oka, Suita-shi, Osaka 565-0871 (Japan)

    2006-09-01

    The C-terminal catalytic domain of P. multocida toxin, which is the virulence factor of the organism in P. multocida, has been expressed, purified and subsequently crystallized using the sitting-drop vapour-diffusion technique. The C-terminal catalytic domain of Pasteurella multocida toxin, which is the virulence factor of the organism in P. multocida, has been expressed, purified and subsequently crystallized using the sitting-drop vapour-diffusion technique. Native diffraction data to 1.9 Å resolution were obtained at the BL44XU beamline of SPring-8 from a flash-frozen crystal at 100 K. The crystals belong to space group C2, with unit-cell parameters a = 111.0, b = 150.4, c = 77.1 Å, β = 105.5°, and are likely to contain one C-PMT (726 residues) per asymmetric unit.

  8. Block copolymer hollow fiber membranes with catalytic activity and pH-response

    KAUST Repository

    Hilke, Roland

    2013-08-14

    We fabricated block copolymer hollow fiber membranes with self-assembled, shell-side, uniform pore structures. The fibers in these membranes combined pores able to respond to pH and acting as chemical gates that opened above pH 4, and catalytic activity, achieved by the incorporation of gold nanoparticles. We used a dry/wet spinning process to produce the asymmetric hollow fibers and determined the conditions under which the hollow fibers were optimized to create the desired pore morphology and the necessary mechanical stability. To induce ordered micelle assembly in the doped solution, we identified an ideal solvent mixture as confirmed by small-angle X-ray scattering. We then reduced p-nitrophenol with a gold-loaded fiber to confirm the catalytic performance of the membranes. © 2013 American Chemical Society.

  9. Atropisomeric chiral dienes in asymmetric catalysis: C(2) -symmetric (Z,Z)-2,3-bis[1-(diphenylphosphinyl)ethylidene]tetralin as a highly active Lewis base organocatalyst.

    Science.gov (United States)

    Ogasawara, Masamichi; Kotani, Shunsuke; Nakajima, Hikaru; Furusho, Haruka; Miyasaka, Mitsuru; Shimoda, Yasushi; Wu, Wei-Yi; Sugiura, Masaharu; Takahashi, Tamotsu; Nakajima, Makoto

    2013-12-16

    Diene catalysts with a twist: The title C2 -symmetric tetralin-fused 1,3-butadiene derivative is atropisomeric and can be resolved into the two helical enantiomers. The optically pure compound showed excellent enantioselectivity as well as unusually high catalytic activity as a chiral Lewis basic organocatalyst in the asymmetric allylation of various aldehydes with β-substituted allyltrichlorosilanes. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Contact structure for use in catalytic distillation

    Science.gov (United States)

    Jones, Jr., Edward M.

    1984-01-01

    A method for conducting catalytic chemical reactions and fractionation of the reaction mixture comprising feeding reactants into a distillation column reactor contracting said reactant in liquid phase with a fixed bed catalyst in the form of a contact catalyst structure consisting of closed porous containers containing the catatlyst for the reaction and a clip means to hold and support said containers, which are disposed above, i.e., on the distillation trays in the tower. The trays have weir means to provide a liquid level on the trays to substantially cover the containers. In other words, the trays function in their ordinary manner with the addition thereto of the catalyst. The reaction mixture is concurrently fractionated in the column.

  11. Oscillatory behaviour of catalytic properties, structure and temperature during the catalytic partial oxidation of methane on Pd/Al2O3

    DEFF Research Database (Denmark)

    Kimmerle, B.; Baiker, A.; Grunwaldt, Jan-Dierk

    2010-01-01

    Pd/Al2O3 catalysts showed an oscillatory behaviour during the catalytic partial oxidation (CPO) of methane, which was investigated simultaneously by IR-thermography, X-ray absorption spectroscopy, and online mass-spectrometry to correlate the temperature, state of the catalyst and catalytic...... to self-reduction leading to extinction of the process. The latter was the key driver for the oscillations and thus gave additional insight into the mechanism of partial methane oxidation....

  12. Conditions for Stable Chip Breaking and Provision of Machined Surface Quality While Turning with Asymmetric Tool Vibrations

    OpenAIRE

    Шелег, В. К.; Молочко, В. И.; Данильчик, С. С.

    2015-01-01

    The paper considers a process of turning structural steel with asymmetric tool vibrations directed along feeding. Asymmetric vibrations characterized by asymmetry coefficient of vibration cycle, their frequency and amplitude are additionally transferred to the tool in the turning process with the purpose to crush chips. Conditions of stable chip breaking and obtaining optimum dimensions of chip elements have been determined in the paper. In order to reduce a negative impact of the vibration a...

  13. Electro Catalytic Oxidation (ECO) Operation

    Energy Technology Data Exchange (ETDEWEB)

    Morgan Jones

    2011-03-31

    The power industry in the United States is faced with meeting many new regulations to reduce a number of air pollutants including sulfur dioxide, nitrogen oxides, fine particulate matter, and mercury. With over 1,000 power plants in the US, this is a daunting task. In some cases, traditional pollution control technologies such as wet scrubbers and SCRs are not feasible. Powerspan's Electro-Catalytic Oxidation, or ECO{reg_sign} process combines four pollution control devices into a single integrated system that can be installed after a power plant's particulate control device. Besides achieving major reductions in emissions of sulfur dioxide (SO{sub 2}), nitrogen oxides (NOx), fine particulate matter (PM2.5) and mercury (Hg), ECO produces a highly marketable fertilizer, which can help offset the operating costs of the process system. Powerspan has been operating a 50-MW ECO commercial demonstration unit (CDU) at FirstEnergy Corp.'s R.E. Burger Plant near Shadyside, Ohio, since February 2004. In addition to the CDU, a test loop has been constructed beside the CDU to demonstrate higher NOx removal rates and test various scrubber packing types and wet ESP configurations. Furthermore, Powerspan has developed the ECO{reg_sign}{sub 2} technology, a regenerative process that uses a proprietary solvent to capture CO{sub 2} from flue gas. The CO{sub 2} capture takes place after the capture of NOx, SO{sub 2}, mercury, and fine particulate matter. Once the CO{sub 2} is captured, the proprietary solution is regenerated to release CO{sub 2} in a form that is ready for geological storage or beneficial use. Pilot scale testing of ECO{sub 2} began in early 2009 at FirstEnergy's Burger Plant. The ECO{sub 2} pilot unit is designed to process a 1-MW flue gas stream and produce 20 tons of CO{sub 2} per day, achieving a 90% CO{sub 2} capture rate. The ECO{sub 2} pilot program provided the opportunity to confirm process design and cost estimates, and prepare for large

  14. Catalytic combustion in gas stoves - Phase II

    Energy Technology Data Exchange (ETDEWEB)

    Hjelm, Anna-Karin [CATATOR AB, Lund (Sweden)

    2003-06-01

    Several independent studies show that gas stoves to some degree contribute to the indoor emissions of NO{sub x} especially in situations were the ventilation flow is poor. The peak-NO{sub x} concentrations can reach several hundred ppb but the integral concentration seldom exceeds about 20 - 50 ppb, which corresponds to an indoor-outdoor ratio of about 1 - 2.5. Epidemiological studies indicate increasing problems with respiratory symptoms in sensitive people at concentrations as low as 15 ppb of NO{sub 2}. Consequently, the NO{sub x}-concentration in homes where gas stoves are used is high enough to cause health effects. However, in situations where the ventilation flow is high (utilisation of ventilation hoods) the NO{sub x}-emissions are not likely to cause any health problems. This study has been aimed at investigating the possibilities to reduce the NO{sub x} emissions from gas stoves by replacing the conventional flame combustion with catalytic combustion. The investigation is requested by Swedish Gas Center, and is a following-up work of an earlier conducted feasibility study presented in April-2002. The present investigation reports on the possibility to use cheap and simple retro-fit catalytic design suggestions for traditional gas stoves. Experiments have been conducted with both natural and town gas, and parameters such as emissions of NO{sub x}, CO and unburned fuel gas and thermal efficiency, etc, have been examined and are discussed. The results show that it is possible to reduce the NO{sub x} emissions up to 80% by a simple retro-fit installation, without decreasing the thermal efficiency of the cooking plate. The measured source strengths correspond to indoor NO{sub x} concentrations that are below or equal to the average outdoor concentration, implying that no additional detrimental health effects are probable. The drawback of the suggested installations is that the concentration of CO and in some cases also CH{sub 4} are increased in the flue gases

  15. Structured materials for catalytic and sensing applications

    Science.gov (United States)

    Hokenek, Selma

    been synthesized and characterized to establish the effects of nanoparticle size on catalytic activity in methanol decomposition. The physicochemical properties of the synthesized palladium-nickel nanoparticles will be discussed, as a function of the synthesis parameters. The optical characteristics of the Ag and Pd nanoparticles will be determined, with a view toward tuning the response of the nanoparticles for incorporation in sensors. Analysis of the monometallic palladium particles revealed a dependence of syngas production on nanoparticle size. The peak and steady state TOFs increased roughly linearly with the average nanoparticle diameter. The amount of coke deposited on the particle surfaces was found to be independent on the size of the nanoparticles. Shape control of the nickel-palladium nanoparticles with a high selectivity for (100) and (110) facets (≤ 80%) has been demonstrated. The resulting alloy nanoparticles were found to have homogeneous composition throughout their volume and maintain FCC crystal structure. Substitution of Ni atoms in the Pd lattice at a 1:3 molar ratio was found to induce lattice strains of ~1%. The Ag nanocubes synthesized exhibited behavior very similar to literature values, when taken on their own, exhibiting a pair of distinct absorbance peaks at 350 nm and 455 nm. In physical mixtures with the Pd nanoparticles synthesized, their behavior showed that the peak position of the Ag nanocubes' absorbance in UV-Vis could be tuned based on the relative proportions of the Ag and Pd nanoparticles present in the suspension analysed. The Ag polyhedra synthesized for comparison showed a broad doublet peak throughout the majority of the visible range before testing as a component in a physical mixture with the Pd nanoparticles. The addition of Pd nanoparticles to form a physical mixture resulted in some damping of the doublet peak observed as well as a corresponding shift in the baseline absorbance proportional to the amount of Pd added to

  16. Asymmetric transition disks: Vorticity or eccentricity?

    NARCIS (Netherlands)

    Ataiee, S.; Pinilla, P.; Zsom, A.; Dullemond, C.P.; Dominik, C.; Ghanbari, J.

    2013-01-01

    Context. Transition disks typically appear in resolved millimeter observations as giant dust rings surrounding their young host stars. More accurate observations with ALMA have shown several of these rings to be in fact asymmetric: they have lopsided shapes. It has been speculated that these rings

  17. MHD stability of vertically asymmetric tokamak equilibria

    International Nuclear Information System (INIS)

    Dalhed, H.E.; Grimm, R.C.; Johnson, J.L.

    1981-03-01

    The ideal MHD stability properties of a special class of vertically asymmetric tokamak equilibria are examined. The calculations confirm that no major new physical effects are introduced and the modifications can be understood by conventional arguments. The results indicate that significant departures from up-down symmetry can be tolerated before the reduction in β becomes important for reactor operation

  18. Organocatalytic asymmetric transfer hydrogenation of imines

    NARCIS (Netherlands)

    de Vries, Johannes G.; Mrsic, Natasa; Mršić, Nataša

    2011-01-01

    The asymmetric organocatalytic transfer hydrogenation of imines can be accomplished in good yields with high enantioselectivities through the use of BINOL-derived phosphoric acids as catalysts and Hantzsch esters or benzothiazoles as the hydride source. The same method can also be applied to the

  19. Asymmetric Hydrogenation of 3-Substituted Pyridinium Salts

    NARCIS (Netherlands)

    Renom-Carrasco, Marc; Gajewski, Piotr; Pignataro, Luca; de Vries, Johannes G.; Piarulli, Umberto; Gennari, Cesare; Lefort, Laurent

    2016-01-01

    The use of an equivalent amount of an organic base leads to high enantiomeric excess in the asymmetric hydrogenation of N-benzylated 3-substituted pyridinium salts into the corresponding piperidines. Indeed, in the presence of Et3N, a Rh-JosiPhos catalyst reduced a range of pyridinium salts with ee

  20. Modelling asymmetric growth in crowded plant communities

    DEFF Research Database (Denmark)

    Damgaard, Christian

    2010-01-01

    -asymmetric growth part, where growth is assumed to be proportional to a power function of the size of the individual, and a term that reduces the relative growth rate as a decreasing function of the individual plant size and the competitive interactions from other plants in the neighbourhood....

  1. Mixed gas plasticization phenomena in asymmetric membranes

    NARCIS (Netherlands)

    Visser, Tymen

    2006-01-01

    This thesis describes the thorough investigation of mixed gas transport behavior of asymmetric membranes in the separation of feed streams containing plasticizing gases in order to gain more insights into the complicated behavior of plasticization. To successfully employ gas separation membranes in

  2. Asymmetrical Representation of Gender in Amharic | Leyew ...

    African Journals Online (AJOL)

    Asymmetrical Representation of Gender in Amharic. ... In gender linguistics, it is customary to observe the correlation between language and socially constructed gender roles. Language users show male and female language ... and novels written in Amharic). Key words: Language, Society, Gender, Pragmatics, Correlation ...

  3. The Asymmetric Predictive Effects of Investor Sentiment

    DEFF Research Database (Denmark)

    Lutz, Chandler

    that the relationship between sentiment and returns is asymmetric: during bear markets, high sentiment predicts low future returns for the cross-section of speculative stocks and the market overall while the relationship during bull markets is weak and often insignicant. Thus, the results suggest that sophisticated...

  4. The Asymmetric Effects of Investor Sentiment

    DEFF Research Database (Denmark)

    Lutz, Chandler

    2016-01-01

    are asymmetric: During peak-to-trough periods of investor sentiment (sentiment contractions), high sentiment predicts low future returns for the cross section of speculative stocks and for the market overall, whereas the relationship between sentiment and future returns is positive but relatively weak during...

  5. Motion in an Asymmetric Double Well

    OpenAIRE

    Brizard, Alain J.; Westland, Melissa C.

    2016-01-01

    The problem of the motion of a particle in an asymmetric double well is solved explicitly in terms of the Weierstrass and Jacobi elliptic functions. While the solution of the orbital motion is expressed simply in terms of the Weierstrass elliptic function, the period of oscillation is more directly expressed in terms of periods of the Jacobi elliptic functions.

  6. Spectral inequalities for the quantum asymmetric top

    Energy Technology Data Exchange (ETDEWEB)

    Bourget, Alain; McMillen, Tyler [Department of Mathematics, California State University (Fullerton), McCarthy Hall 154, Fullerton, CA 92834 (United States)], E-mail: abourget@fullerton.edu, E-mail: tmcmillen@fullerton.edu

    2009-03-06

    We consider the spectrum of the quantum asymmetric top. Unlike in the case when two or three moments of inertia are equal, when the moments of inertia are distinct all degeneracy in the spectrum of the operator is removed. We derive inequalities for the spectra based on recent results on the interlacing of Van Vleck zeros.

  7. Computing modal dispersion characteristics of radially Asymmetric ...

    African Journals Online (AJOL)

    We developed a matrix theory that applies to with non-circular/circular but concentric layers fibers. And we compute the dispersion characteristics of radially unconventional fiber, known as Asymmetric Bragg fiber. An attempt has been made to determine how the modal characteristics change as circular Bragg fiber is ...

  8. The endoplasmic reticulum is partitioned asymmetrically during mitosis before cell fate selection in proneuronal cells in the early Drosophila embryo

    Science.gov (United States)

    Eritano, Anthony S.; Altamirano, Arturo; Beyeler, Sarah; Gaytan, Norma; Velasquez, Mark; Riggs, Blake

    2017-01-01

    Asymmetric cell division is the primary mechanism to generate cellular diversity, and it relies on the correct partitioning of cell fate determinants. However, the mechanism by which these determinants are delivered and positioned is poorly understood, and the upstream signal to initiate asymmetric cell division is unknown. Here we report that the endoplasmic reticulum (ER) is asymmetrically partitioned during mitosis in epithelial cells just before delamination and selection of a proneural cell fate in the early Drosophila embryo. At the start of gastrulation, the ER divides asymmetrically into a population of asynchronously dividing cells at the anterior end of the embryo. We found that this asymmetric division of the ER depends on the highly conserved ER membrane protein Jagunal (Jagn). RNA inhibition of jagn just before the start of gastrulation disrupts this asymmetric division of the ER. In addition, jagn-deficient embryos display defects in apical-basal spindle orientation in delaminated embryonic neuroblasts. Our results describe a model in which an organelle is partitioned asymmetrically in an otherwise symmetrically dividing cell population just upstream of cell fate determination and updates previous models of spindle-based selection of cell fate during mitosis. PMID:28381427

  9. Charge asymmetric cosmic rays as a probe of flavor violating asymmetric dark matter

    Energy Technology Data Exchange (ETDEWEB)

    Masina, Isabella [Dipartimento di Fisica, Università di Ferrara and INFN Sez. di Ferrara, Via Saragat 1, I-44100 Ferrara (Italy); Sannino, Francesco, E-mail: masina@fe.infn.it, E-mail: sannino@cp3-origins.net [CP3-Origins and DIAS, University of Southern Denmark, Campusvej 55, DK-5230 Odense M (Denmark)

    2011-09-01

    The recently introduced cosmic sum rules combine the data from PAMELA and Fermi-LAT cosmic ray experiments in a way that permits to neatly investigate whether the experimentally observed lepton excesses violate charge symmetry. One can in a simple way determine universal properties of the unknown component of the cosmic rays. Here we attribute a potential charge asymmetry to the dark sector. In particular we provide models of asymmetric dark matter able to produce charge asymmetric cosmic rays. We consider spin zero, spin one and spin one-half decaying dark matter candidates. We show that lepton flavor violation and asymmetric dark matter are both required to have a charge asymmetry in the cosmic ray lepton excesses. Therefore, an experimental evidence of charge asymmetry in the cosmic ray lepton excesses implies that dark matter is asymmetric.

  10. Phosphazene additives

    Science.gov (United States)

    Harrup, Mason K; Rollins, Harry W

    2013-11-26

    An additive comprising a phosphazene compound that has at least two reactive functional groups and at least one capping functional group bonded to phosphorus atoms of the phosphazene compound. One of the at least two reactive functional groups is configured to react with cellulose and the other of the at least two reactive functional groups is configured to react with a resin, such as an amine resin of a polycarboxylic acid resin. The at least one capping functional group is selected from the group consisting of a short chain ether group, an alkoxy group, or an aryloxy group. Also disclosed are an additive-resin admixture, a method of treating a wood product, and a wood product.

  11. Catalytic hot gas cleaning of gasification gas

    Energy Technology Data Exchange (ETDEWEB)

    Simell, P. [VTT Energy, Espoo (Finland). Energy Production Technologies

    1997-12-31

    The aim of this work was to study the catalytic cleaning of gasification gas from tars and ammonia. In addition, factors influencing catalytic activity in industrial applications were studied, as well as the effects of different operation conditions and limits. Also the catalytic reactions of tar and ammonia with gasification gas components were studied. The activities of different catalyst materials were measured with laboratory-scale reactors fed by slip streams taken from updraft and fluid bed gasifiers. Carbonate rocks and nickel catalysts proved to be active tar decomposing catalysts. Ammonia decomposition was in turn facilitated by nickel catalysts and iron materials like iron sinter and iron dolomite. Temperatures over 850 deg C were required at 2000{sup -1} space velocity at ambient pressure to achieve almost complete conversions. During catalytic reactions H{sub 2} and CO were formed and H{sub 2}O was consumed in addition to decomposing hydrocarbons and ammonia. Equilibrium gas composition was almost achieved with nickel catalysts at 900 deg C. No deactivation by H{sub 2}S or carbon took place in these conditions. Catalyst blocking by particulates was avoided by using a monolith type of catalyst. The apparent first order kinetic parameters were determined for the most active materials. The activities of dolomite, nickel catalyst and reference materials were measured in different gas atmospheres using laboratory apparatus. This consisted of nitrogen carrier, toluene as tar model compound, ammonia and one of the components H{sub 2}, H{sub 2}O, CO, CO{sub 2}, CO{sub 2}+H{sub 2}O or CO+CO{sub 2}. Also synthetic gasification gas was used. With the dolomite and nickel catalyst the highest toluene decomposition rates were measured with CO{sub 2} and H{sub 2}O. In gasification gas, however, the rate was retarded due to inhibition by reaction products (CO, H{sub 2}, CO{sub 2}). Tar decomposition over dolomite was modelled by benzene reactions with CO{sub 2}, H

  12. Disulfide bond-stabilized physical gels of an asymmetric collagen-inspired telechelic protein polymer

    NARCIS (Netherlands)

    Pham, T.H.T.; Skrzeszewska, P.J.; Werten, M.W.T.; Rombouts, W.H.; Cohen Stuart, M.A.; Wolf, de F.A.; Gucht, van der J.

    2013-01-01

    We designed and produced an asymmetric collagen-inspired telechelic protein polymer with end blocks that can form triple helices of different thermal stabilities. Both end blocks consist of a motif that can form triple helices at low temperature, but one of these blocks carries an additional

  13. α-Ketophosphonates as ester surrogates: isothiourea-catalyzed asymmetric diester and lactone synthesis.

    Science.gov (United States)

    Smith, Siobhan R; Leckie, Stuart M; Holmes, Reuben; Douglas, James; Fallan, Charlene; Shapland, Peter; Pryde, David; Slawin, Alexandra M Z; Smith, Andrew D

    2014-05-02

    Isothiourea HBTM-2.1 catalyzes the asymmetric Michael addition/lactonization of aryl- and alkenylacetic acids using α-keto-β,γ-unsaturated phosphonates as α,β-unsaturated ester surrogates, giving access to a diverse range of stereodefined lactones or enantioenriched functionalized diesters upon ring-opening.

  14. Asymmetric hydrogenation of quinolines catalyzed by iridium complexes of monodentate BINOL-derived phosphoramidites

    NARCIS (Netherlands)

    Mrsic, Natasa; Lefort, Laurent; Boogers, Jeroen A. F.; Minnaard, Adriaan J.; Feringa, Ben L.; de Vries, Johannes G.; Mršić, Nataša

    The monodentate BINOL-derived phosphoramidite PipPhos is used as ligand for the iridium-catalyzed asymmetric hydrogenation of 2- and 2,6-substituted quinolines. If tri-ortho-tolylphosphine and/or chloride salts are used as additives enantioselectivities are strongly enhanced up to 89%. NMR indicates

  15. A General Asymmetric Synthesis of (R-Matsutakeol and Flavored Analogs

    Directory of Open Access Journals (Sweden)

    Jia Liu

    2017-02-01

    Full Text Available An efficient and practical synthetic route toward chiral matsutakeol and analogs was developed by asymmetric addition of terminal alkyne to aldehydes. (R-matsutakeol and other flavored substances were feasibly synthesized from various alkylaldehydes in high yield (up to 49.5%, in three steps and excellent enantiomeric excess (up to >99%. The protocols may serve as an alternative asymmetric synthetic method for active small-molecule library of natural fatty acid metabolites and analogs. These chiral allyl alcohols are prepared for food analysis and screening insect attractants.

  16. Adhesion mechanism of a gecko-inspired oblique structure with an adhesive tip for asymmetric detachment

    International Nuclear Information System (INIS)

    Sekiguchi, Yu; Sato, Chiaki; Takahashi, Kunio

    2015-01-01

    An adhesion model of an oblique structure with an adhesive tip is proposed by considering a limiting stress for adhesion to describe the detachment mechanism of gecko foot hairs. When a force is applied to the root of the oblique structure, normal and shear stresses are generated at contact and the adhesive tip is detached from the surface when reaching the limiting stress. An adhesion criterion that considers both the normal and shear stresses is introduced, and the asymmetric detachment of the oblique structure is theoretically investigated. In addition, oblique beam array structures are manufactured, and an inclination effect of the structure on the asymmetric detachment is experimentally verified. (paper)

  17. Development of asymmetric stent for treatment of eccentric plaque.

    Science.gov (United States)

    Syaifudin, Achmad; Takeda, Ryo; Sasaki, Katsuhiko

    2018-01-01

    The selection of stent and balloon type is decisive in the stenting process. In the treatment of an eccentric plaque obstruction, a symmetric expansion from stent dilatation generates nonuniform stress distribution, which may aggravate fibrous cap prone to rupture. This paper developed a new stent design to treat eccentric plaque using structural transient dynamic analysis in ANSYS. A non-symmetric structural geometry of stent is generated to obtain reasonable stress distribution safe for the arterial layer surrounding the stent. To derive the novel structural geometry, a Sinusoidal stent type is modified by varying struts length and width, adding bridges, and varying curvature width of struts. An end ring of stent struts was also modified to eliminate dogboning phenomenon and to reduce the Ectropion angle. Two balloon types were used to deploy the stent, an ordinary cylindrical and offset balloon. Positive modification results were used to construct the final non-symmetric stent design, called an Asymmetric stent. Analyses of the deformation characteristics, changes in surface roughness and induced stresses within intact arterial layer were subsequently examined. Interaction between the stent and vessel wall was implemented by means of changes in surface roughness and stress distribution analyses. The Palmaz and the Sinusoidal stent were used for a comparative study. This study indicated that the Asymmetric stent types reduced the central radial recoiling and the dogboning phenomenon. In terms of changes in surface roughness and induced stresses, the Asymmetric stent has a comparable effect with that of the Sinusoidal stent. In addition, it could enhance the distribution of surface roughening as expanded by an offset balloon.

  18. A mean-field theory on the differential capacitance of asymmetric ionic liquid electrolytes.

    Science.gov (United States)

    Han, Yining; Huang, Shanghui; Yan, Tianying

    2014-07-16

    The size of ions significantly influences the electric double layer structure of room temperature ionic liquid (IL) electrolytes and their differential capacitance (Cd). In this study, we extended the mean-field theory (MFT) developed independently by Kornyshev (2007J. Phys. Chem. B 111 5545-57) and Kilic, Bazant, and Ajdari (2007 Phys. Rev. E 75 021502) (the KKBA MFT) to take into account the asymmetric 1:1 IL electrolytes by introducing an additional parameter ξ for the anion/cation volume ratio, besides the ionic compressibility γ in the KKBA MFT. The MFT of asymmetric ions becomes KKBA MFT upon ξ = 1, and further reduces to Gouy-Chapman theory in the γ → 0 limit. The result of the extended MFT demonstrates that the asymmetric ILs give rise to an asymmetric Cd, with the higher peak in Cd occurring at positive polarization for the smaller anionic size. At high potential, Cd decays asymptotically toward KKBA MFT characterized by γ for the negative polarization, and characterized by ξγ for the positive polarization, with inverse-square-root behavior. At low potential, around the potential of zero charge, the asymmetric ions cause a higher Cd, which exceeds that of Gouy-Chapman theory.

  19. C. elegans HAM-1 functions in the nucleus to regulate asymmetric neuroblast division.

    Science.gov (United States)

    Leung, Amy; Hua, Khang; Ramachandran, Pavitra; Hingwing, Kyla; Wu, Maria; Koh, Pei Luan; Hawkins, Nancy

    2016-02-01

    All 302 neurons in the C. elegans hermaphrodite arise through asymmetric division of neuroblasts. During embryogenesis, the C. elegans ham-1 gene is required for several asymmetric neuroblast divisions in lineages that generate both neural and apoptotic cells. By antibody staining, endogenous HAM-1 is found exclusively at the cell cortex in many cells during embryogenesis and is asymmetrically localized in dividing cells. Here we show that in transgenic embryos expressing a functional GFP::HAM-1 fusion protein, GFP expression is also detected in the nucleus, in addition to the cell cortex. Consistent with the nuclear localization is the presence of a putative DNA binding winged-helix domain within the N-terminus of HAM-1. Through a deletion analysis we determined that the C-terminus of the protein is required for nuclear localization and we identified two nuclear localization sequences (NLSs). A subcellular fractionation experiment from wild type embryos, followed by Western blotting, revealed that endogenous HAM-1 is primarily found in the nucleus. Our analysis also showed that the N-terminus is necessary for cortical localization. While ham-1 function is essential for asymmetric division in the lineage that generates the PLM mechanosensory neuron, we showed that cortical localization may not required. Thus, our results suggest that there is a nuclear function for HAM-1 in regulating asymmetric neuroblast division and that the requirement for cortical localization may be lineage dependent. Copyright © 2015 Elsevier Inc. All rights reserved.

  20. Catalytic Organometallic Reactions of Ammonia

    Science.gov (United States)

    Klinkenberg, Jessica L.

    2012-01-01

    Until recently, ammonia had rarely succumbed to catalytic transformations with homogeneous catalysts, and the development of such reactions that are selective for the formation of single products under mild conditions has encountered numerous challenges. However, recently developed catalysts have allowed several classes of reactions to create products with nitrogen-containing functional groups from ammonia. These reactions include hydroaminomethylation, reductive amination, alkylation, allylic substitution, hydroamination, and cross-coupling. This Minireview describes examples of these processes and the factors that control catalyst activity and selectivity. PMID:20857466

  1. Studies of Catalytic Model Systems

    DEFF Research Database (Denmark)

    Holse, Christian

    of the Cu/ZnO nanoparticles is highly relevant to industrial methanol synthesis for which the direct interaction of Cu and ZnO nanocrystals synergistically boost the catalytic activity. The dynamical behavior of the nanoparticles under reducing and oxidizing environments were studied by means of ex situ X...... as the nanoparticles are reduced. The Cu/ZnO nanoparticles are tested on a  µ-reactor platform and prove to be active towards methanol synthesis, making it an excellent model system for further investigations into activity depended morphology changes....

  2. Catalytic Combustion of Ethyl Acetate

    OpenAIRE

    ÖZÇELİK, Tuğba GÜRMEN; ATALAY, Süheyda; ALPAY, Erden

    2014-01-01

    The catalytic combustion of ethyl acetate over prepared metal oxide catalysts was investigated. CeO, Co2O3, Mn2O3, Cr2O3, and CeO-Co2O3 catalysts were prepared on monolith supports and they were tested. Before conducting the catalyst experiments, we searched for the homogeneous gas phase combustion reaction of ethyl acetate. According to the homogeneous phase experimental results, 45% of ethyl acetate was converted at the maximum reactor temperature tested (350 °C). All the prepare...

  3. Kinetics of heterogeneous catalytic reactions

    CERN Document Server

    Boudart, Michel

    2014-01-01

    This book is a critical account of the principles of the kinetics of heterogeneous catalytic reactions in the light of recent developments in surface science and catalysis science. Originally published in 1984. The Princeton Legacy Library uses the latest print-on-demand technology to again make available previously out-of-print books from the distinguished backlist of Princeton University Press. These paperback editions preserve the original texts of these important books while presenting them in durable paperback editions. The goal of the Princeton Legacy Library is to vastly increase acc

  4. Vibration analysis of paper machine's asymmetric tube roll supported by spherical roller bearings

    Science.gov (United States)

    Heikkinen, Janne E.; Ghalamchi, Behnam; Viitala, Raine; Sopanen, Jussi; Juhanko, Jari; Mikkola, Aki; Kuosmanen, Petri

    2018-05-01

    This paper presents a simulation method that is used to study subcritical vibrations of a tube roll in a paper machine. This study employs asymmetric 3D beam elements based on the Timoshenko beam theory. An asymmetric beam model accounts for varying stiffness and mass distributions. Additionally, a detailed rolling element bearing model defines the excitations arising from the set of spherical roller bearings at both ends of the rotor. The results obtained from the simulation model are compared against the results from the measurements. The results indicate that the waviness of the bearing rolling surfaces contributes significantly to the subcritical vibrations while the asymmetric properties of the tube roll have only a fractional effect on the studied vibrations.

  5. Preparation of Mesoporous SBA-16 Silica-Supported Biscinchona Alkaloid Ligand for the Asymmetric Dihydroxylation of Olefins

    Directory of Open Access Journals (Sweden)

    Shaheen M. Sarkar

    2014-01-01

    Full Text Available Optically active cinchona alkaloid was anchored onto mesoporous SBA-16 silica and the as-prepared complex was used as a heterogeneous chiral ligand of osmium tetraoxide for the asymmetric dihydroxylation of olefins. The prepared catalytic system provided 90–93% yield of vicinal diol with 92–99% enantioselectivity. The ordered mesoporous SBA-16 silica was found to be a valuable support for the cinchona alkaloid liganded osmium catalyst system which is frequently used in chemical industries and research laboratories for olefin functionalization.

  6. Catalytic enantioselective Reformatsky reaction with ketones

    NARCIS (Netherlands)

    Fernandez-Ibanez, M. Angeles; Macia, Beatriz; Minnaard, Adriaan J.; Feringa, Ben L.

    2008-01-01

    Chiral tertiary alcohols were obtained with good yields and enantioselectivities via a catalytic Reformatsky reaction with ketones, including the challenging diaryl ketones, using chiral BINOL derivatives.

  7. Asymmetric epoxidation of cis/trans-β-methylstyrene catalysed by immobilised Mn(salen) with different linkages: heterogenisation of homogeneous asymmetric catalysis.

    Science.gov (United States)

    Zhang, Haidong; Zou, Yu; Wang, Yi-Meng; Shen, Yu; Zheng, Xuxu

    2014-06-16

    Immobilised Mn(salen) catalysts with two different linkages were studied in the asymmetric epoxidation of cis/trans-β-methylstyrene using NaClO as oxidant. The immobilised Mn(salen) complexes inside nanopores can lead to different catalytic behaviour compared with that of homogeneous Jacobsen catalyst. The rigidity of the linkage was found to be a key factor affecting the catalytic performance of immobilised catalysts. The immobilised catalyst with a rigid linkage exhibited comparable chemical selectivity, enantioselectivity and cis/trans ratio of product formation to that obtained with homogeneous Jacobsen catalysts. In contrast, the immobilised catalyst with a flexible linkage gave remarkably lower chemical selectivity, enantioselectivity and inverted cis/trans ratio compared with the results obtained with the homogeneous Jacobsen catalyst and the immobilised catalyst with rigid linkage. Thus, for immobilised Mn(salen) catalysts, a rigid linkage connecting active centres to the support is essential to obtain activity and enantioselectivity as high as those obtained in homogeneous systems. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. The Effect of Labor Supply Shortages on Asymmetric Cost Behavior

    DEFF Research Database (Denmark)

    Hoffmann, Kira

    This study examines the effect of shortages in labor supply on asymmetric cost behavior. Building on the labor demand literature, it is argued that labor supply shortages increase adjustment costs for hiring new employees. Consistent with this explanation, results provide evidence that companies...... facing restrictions in labor supply increase costs (and resources) less than companies operating with sufficient access to additional personnel. This leads to a more symmetrical cost behavior for increasing activity compared to decreasing activity. Additional analyses show that shortages in labor supply...... induce firms to increase selling prices but also to temporarily expect more effort from their current employees. The effect decreases with the length of the labor supply shock and is more pronounced for companies located in less populated regions. Results are robust to alternative explanations...

  9. Catalytic conversion of light alkanes

    Energy Technology Data Exchange (ETDEWEB)

    Lyons, J.E.

    1992-06-30

    The second Quarterly Report of 1992 on the Catalytic Conversion of Light Alkanes reviews the work done between April 1, 1992 and June 31, 1992 on the Cooperative Agreement. The mission of this work is to devise a new catalyst which can be used in a simple economic process to convert the light alkanes in natural gas to oxygenate products that can either be used as clean-burning, high octane liquid fuels, as fuel components or as precursors to liquid hydrocarbon uwspomdon fuel. During the past quarter we have continued to design, prepare, characterize and test novel catalysts for the mild selective reaction of light hydrocarbons with air or oxygen to produce alcohols directly. These catalysts are designed to form active metal oxo (MO) species and to be uniquely active for the homolytic cleavage of the carbon-hydrogen bonds in light alkanes producing intermediates which can form alcohols. We continue to investigate three molecular environments for the active catalytic species that we are trying to generate: electron-deficient macrocycles (PHASE I), polyoxometallates (PHASE II), and regular oxidic lattices including zeolites and related structures as well as other molecular surface structures having metal oxo groups (PHASE I).

  10. A study on the reaction characteristics of vanadium-impregnated natural manganese oxide in ammonia selective catalytic reduction.

    Science.gov (United States)

    Kim, Sung Su; Lee, Sang Moon; Park, Kwang Hee; Kwon, Dong Wook; Hong, Sung Chang

    2011-05-01

    This study investigated the effect of adding vanadium (V) to natural manganese oxide (NMO) in ammonia (NH3) selective catalytic reduction (SCR). The addition of V to NMO decreased the catalytic activity at low temperatures by blocking the active site. However, the enhancement of catalytic activity was achieved by controlling NH3 oxidation at high temperatures. From the NH3 temperature programmed desorption and oxygen on/off test, it was confirmed that the amount of Lewis acid site and active lattice oxygen of the catalyst affects the catalytic performance at low temperature.

  11. Development of a high-temperature durable catalyst for use in catalytic combustors for advanced automotive gas turbine engines

    Science.gov (United States)

    Tong, H.; Snow, G. C.; Chu, E. K.; Chang, R. L. S.; Angwin, M. J.; Pessagno, S. L.

    1981-01-01

    Durable catalytic reactors for advanced gas turbine engines were developed. Objectives were: to evaluate furnace aging as a cost effective catalytic reactor screening test, measure reactor degradation as a function of furnace aging, demonstrate 1,000 hours of combustion durability, and define a catalytic reactor system with a high probability of successful integration into an automotive gas turbine engine. Fourteen different catalytic reactor concepts were evaluated, leading to the selection of one for a durability combustion test with diesel fuel for combustion conditions. Eight additional catalytic reactors were evaluated and one of these was successfully combustion tested on propane fuel. This durability reactor used graded cell honeycombs and a combination of noble metal and metal oxide catalysts. The reactor was catalytically active and structurally sound at the end of the durability test.

  12. Analytical study of the origin and behavior of asymmetric vortices

    Science.gov (United States)

    Tobak, Murray; Degani, David; Zilliac, Gregory G.

    1990-01-01

    An hypothesis advanced originally to explain computational observations is supported by theoretical considerations: The asymmetric mean flow observed on bodies of revolution at moderate to high angles of attack is the result of a convective instability of an originally symmetric flow to a time-invariant space-fixed disturbance. Additionally, the time-dependent fluctuations characteristic of the flow at higher angles of attack (up to 90 deg) are the result of an absolute instability of an originally steady flow to a small temporal disturbance of finite duration. Within a common domain, the instability mechanisms may coexist. The experimentally confirmed existence of bistable states, wherein the side-force variation with nose roll angle approaches a square-wave distribution, is attributed to the dominant influence of a pair of trailing vortices from the ogival forebody. Their existence is made possible by the appearance of foci of separation in the skin-friction line pattern beyond a critical angle of attack. The extreme sensitivity of the asymmetric flow orientation to nose geometry, demonstrated experimentally, is attributed to the presence of an indeterminate phase in the family of possible solutions for the three-dimensional wave system.

  13. Catalytic and Gas-Solid Reactions Involving HCN over Limestone

    DEFF Research Database (Denmark)

    Jensen, Anker; Johnsson, Jan Erik; Dam-Johansen, Kim

    1997-01-01

    In coal-fired combustion systems solid calcium species may be present as ash components or limestone added to the combustion chamber. In this study heterogeneous reactions involving HCN over seven different limestones were investigated in a laboratory fixed-bed quartz reactor at 873-1,173 K....... The results indicate that heterogeneous oxidation of HCN is important in calciners and fluidized-bed combustors with limestone addition or when burning coals with an ash with a high catalytic activity....

  14. Four-Component Catalytic Machinery: Reversible Three-State Control of Organocatalysis by Walking Back and Forth on a Track.

    Science.gov (United States)

    Mittal, Nikita; Özer, Merve S; Schmittel, Michael

    2018-04-02

    A three-component supramolecular walker system is presented where a two-footed ligand (biped) walks back and forth on a tetrahedral 3D track upon the addition and removal of copper(I) ions, respectively. The addition of N-methylpyrrolidine as a catalyst to the walker system generates a four-component catalytic machinery, which acts as a three-state switchable catalytic ensemble in the presence of substrates for a conjugate addition. The copper(I)-ion-initiated walking process of the biped ligand on the track regulates the catalytic activity in three steps: ON versus int ON (intermediate ON) versus OFF. To establish the operation of the four-component catalytic machinery in a mixture of all constituents, forward and backward cycles were performed in situ illustrating that both the walking process and catalytic action are fully reversible and reproducible.

  15. Hydrazides and hydrazones as versatile Michael-Donors for iminium-catalyzed conjugate addition reactions

    OpenAIRE

    Fernández Chento, Maitane

    2014-01-01

    396 : il., graf. In the work compiled in this thesis is presented a series of strategies that have been studied and have lead to the asymmetric synthesis of useful building blocks in high yields and stereochemical control. These are reliant on the use of chiral secondary amines as the element that induces stereocontrol, where the activation of the substrate is based on the formation of an iminium ion intermediate within the catalytic cycle. In this sense, it has been demonstrated that, und...

  16. Bianisotropic metamaterials based on twisted asymmetric crosses

    International Nuclear Information System (INIS)

    Reyes-Avendaño, J A; Sampedro, M P; Juárez-Ruiz, E; Pérez-Rodríguez, F

    2014-01-01

    The effective bianisotropic response of 3D periodic metal-dielectric structures, composed of crosses with asymmetrically-cut wires, is investigated within a general homogenization theory using the Fourier formalism and the form-factor division approach. It is found that the frequency dependence of the effective permittivity for a system of periodically-repeated layers of metal crosses exhibits two strong resonances, whose separation is due to the cross asymmetry. Besides, bianisotropic metamaterials, having a base of four twisted asymmetric crosses, are proposed. The designed metamaterials possess negative refractive index at frequencies determined by the cross asymmetry, the gap between the arms of adjacent crosses lying on the same plane, and the type of Bravais lattice. (papers)

  17. Asymmetric hypsarrhythmia: clinical electroencephalographic and radiological findings.

    Science.gov (United States)

    Drury, I; Beydoun, A; Garofalo, E A; Henry, T R

    1995-01-01

    Twenty-six children (16 boys and 10 girls) with hypsarrhythmia and infantile spasms (IS) were studied at the University of Michigan EEG Laboratory in a 4-year period. Six (2 boys, 4 girls), had asymmetric hypsarrhythmia with a preponderance of both slowing and epileptiform activity over one hemisphere. All 6 had the symptomatic form of IS, 4 with dysplastic conditions, 1 with porencephaly from a cerebral infarct, and 1 with hypoxicischemic encephalopathy. Five children had focal abnormalities on either physical examination or imaging studies. Four had the highest amplitude slowing and most epileptiform activity ipsilateral to the lesion, in 1, it was contralateral. Asymmetric hypsarrhythmia constituted 23% of cases with hypsarrhythmia examined at our EEG laboratory. The significant success in surgical therapy for some children with IS indicates the importance of identifying focal hemispheric abnormalities even if they are not apparent clinically. EEG may suggest focal changes not detected clinically or radiologically.

  18. Improved DFIG Capability during Asymmetrical Grid Faults

    DEFF Research Database (Denmark)

    Zhou, Dao; Blaabjerg, Frede

    2015-01-01

    In the wind power application, different asymmetrical types of the grid fault can be categorized after the Y/d transformer, and the positive and negative components of a single-phase fault, phase-to-phase fault, and two-phase fault can be summarized. Due to the newly introduced negative and even...... the natural component of the Doubly-Fed Induction Generator (DFIG) stator flux during the fault period, their effects on the rotor voltage can be investigated. It is concluded that the phase-to-phase fault has the worst scenario due to its highest introduction of the negative stator flux. Afterwards......, the capability of a 2 MW DFIG to ride through asymmetrical grid faults can be estimated at the existing design of the power electronics converter. Finally, a control scheme aimed to improve the DFIG capability is proposed and the simulation results validate its feasibility....

  19. Asymmetric catalysis in organic synthesis

    Energy Technology Data Exchange (ETDEWEB)

    Reilly, S.D.; Click, D.R.; Grumbine, S.K.; Scott, B.L.; Watkins, J.G.

    1998-11-01

    This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The goal of the project was to prepare new catalyst systems, which would perform chemical reactions in an enantioselective manner so as to produce only one of the possible optical isomers of the product molecule. The authors have investigated the use of lanthanide metals bearing both diolate and Schiff-base ligands as catalysts for the enantioselective reduction of prochiral ketones to secondary alcohols. The ligands were prepared from cheap, readily available starting materials, and their synthesis was performed in a ''modular'' manner such that tailoring of specific groups within the ligand could be carried out without repeating the entire synthetic procedure. In addition, they have developed a new ligand system for Group IV and lanthanide-based olefin polymerization catalysts. The ligand system is easily prepared from readily available starting materials and offers the opportunity to rapidly prepare a wide range of closely related ligands that differ only in their substitution patterns at an aromatic ring. When attached to a metal center, the ligand system has the potential to carry out polymerization reactions in a stereocontrolled manner.

  20. Isospin dependent properties of asymmetric nuclear matter

    OpenAIRE

    Chowdhury, P. Roy; Basu, D. N.; Samanta, C.

    2009-01-01

    The density dependence of nuclear symmetry energy is determined from a systematic study of the isospin dependent bulk properties of asymmetric nuclear matter using the isoscalar and the isovector components of density dependent M3Y interaction. The incompressibility $K_\\infty$ for the symmetric nuclear matter, the isospin dependent part $K_{asy}$ of the isobaric incompressibility and the slope $L$ are all in excellent agreement with the constraints recently extracted from measured isotopic de...

  1. Magnetic properties of strongly asymmetric nuclear matter

    International Nuclear Information System (INIS)

    Kutschera, M.; Wojcik, W.

    1988-01-01

    We investigate stability of neutron matter containing a small proton admixture with respect to spin fluctuations. We establish conditions under which strongly asymmetric nuclear matter could acquire a permanent magnetization. It is shown that if the protons are localized, the system becomes unstable to spin fluctuations for arbitrarily weak proton-neutron spin interactions. For non-localized protons there exists a threshold value of the spin interaction above which the system can develop a spontaneous polarization. 12 refs., 2 figs. (author)

  2. Asymmetric inheritance of cytoophidia in Schizosaccharomyces pombe

    OpenAIRE

    Zhang, Jing; Hulme, Lydia; Liu, Ji-Long

    2014-01-01

    ABSTRACT A general view is that Schizosaccharomyces pombe undergoes symmetric cell division with two daughter cells inheriting equal shares of the content from the mother cell. Here we show that CTP synthase, a metabolic enzyme responsible for the de novo synthesis of the nucleotide CTP, can form filamentous cytoophidia in the cytoplasm and nucleus of S. pombe cells. Surprisingly, we observe that both cytoplasmic and nuclear cytoophidia are asymmetrically inherited during cell division. Our t...

  3. Asymmetric flow events in a VEER 1000

    International Nuclear Information System (INIS)

    Horak, W.C.; Kennett, R.J.; Shier, W.; Guppy, J.G.

    1992-07-01

    This paper describes the simulation of asymmetric loss of flow events in Russian designed VVER-1000 reactors using the RETRAN-02 Mod4 computer code. VVER-1000 reactors have significant differences from United States pressurized water reactors including multi-level emergency response systems and plant operation at reduced power levels with one or more main circulation pumps inoperable. The results of these simulations are compared to similar analyses done by the designers for the Rovno plant

  4. Asymmetric k-Center with Minimum Coverage

    DEFF Research Database (Denmark)

    Gørtz, Inge Li

    2008-01-01

    In this paper we give approximation algorithms and inapproximability results for various asymmetric k-center with minimum coverage problems. In the k-center with minimum coverage problem, each center is required to serve a minimum number of clients. These problems have been studied by Lim et al. [A....... Lim, B. Rodrigues, F. Wang, Z. Xu, k-center problems with minimum coverage, Theoret. Comput. Sci. 332 (1–3) (2005) 1–17] in the symmetric setting....

  5. Asymmetric volatility connectedness on the forex market

    Czech Academy of Sciences Publication Activity Database

    Baruník, Jozef; Kočenda, Evžen; Vácha, Lukáš

    2017-01-01

    Roč. 77, č. 1 (2017), s. 39-56 ISSN 0261-5606 R&D Projects: GA ČR(CZ) GA16-14179S Institutional support: RVO:67985556 Keywords : volatility * connectedness * asymmetric effects Subject RIV: AH - Economics OBOR OECD: Finance Impact factor: 1.853, year: 2016 http://library.utia.cas.cz/separaty/2017/E/barunik-0478477.pdf

  6. Climate Change, Procrastination and Asymmetric Power

    OpenAIRE

    Korkut Alp Ertürk; Jason Whittle

    2015-01-01

    This paper argues that policy conclusions of the economics of climate change literature based on “integrated assessment models” (IAM) fails to take into account the intricacies of collective action. Specifically, IAMs do not account for how asymmetric power between developed and undeveloped countries changes the former's pay off matrix with respect to mitigation and adaptation strategies. Using a simple one-sided prisoner's dilemma model, the paper illustrates how developed countries' power t...

  7. Asymmetric unemployment rate dynamics in Australia

    OpenAIRE

    Gunnar Bardsen; Stan Hurn; Zoe McHugh

    2011-01-01

    The unemployment rate in Australia is modelled as an asymmetric and nonlinear function of aggregate demand, productivity, real interest rates, the replacement ratio and the real exchange rate. If changes in unemployment are big, the management of of demand, real interest rates and the replacement ratio will be good instruments to start bringing it down. The model is developed by exploiting recent developments in automated model-selection procedures.

  8. Asymmetric threat data mining and knowledge discovery

    Science.gov (United States)

    Gilmore, John F.; Pagels, Michael A.; Palk, Justin

    2001-03-01

    Asymmetric threats differ from the conventional force-on- force military encounters that the Defense Department has historically been trained to engage. Terrorism by its nature is now an operational activity that is neither easily detected or countered as its very existence depends on small covert attacks exploiting the element of surprise. But terrorism does have defined forms, motivations, tactics and organizational structure. Exploiting a terrorism taxonomy provides the opportunity to discover and assess knowledge of terrorist operations. This paper describes the Asymmetric Threat Terrorist Assessment, Countering, and Knowledge (ATTACK) system. ATTACK has been developed to (a) data mine open source intelligence (OSINT) information from web-based newspaper sources, video news web casts, and actual terrorist web sites, (b) evaluate this information against a terrorism taxonomy, (c) exploit country/region specific social, economic, political, and religious knowledge, and (d) discover and predict potential terrorist activities and association links. Details of the asymmetric threat structure and the ATTACK system architecture are presented with results of an actual terrorist data mining and knowledge discovery test case shown.

  9. Predicting tensorial electrophoretic effects in asymmetric colloids

    Science.gov (United States)

    Mowitz, Aaron J.; Witten, T. A.

    2017-12-01

    We formulate a numerical method for predicting the tensorial linear response of a rigid, asymmetrically charged body to an applied electric field. This prediction requires calculating the response of the fluid to the Stokes drag forces on the moving body and on the countercharges near its surface. To determine the fluid's motion, we represent both the body and the countercharges using many point sources of drag known as Stokeslets. Finding the correct flow field amounts to finding the set of drag forces on the Stokeslets that is consistent with the relative velocities experienced by each Stokeslet. The method rigorously satisfies the condition that the object moves with no transfer of momentum to the fluid. We demonstrate that a sphere represented by 1999 well-separated Stokeslets on its surface produces flow and drag force like a solid sphere to 1% accuracy. We show that a uniformly charged sphere with 3998 body and countercharge Stokeslets obeys the Smoluchowski prediction [F. Morrison, J. Colloid Interface Sci. 34, 210 (1970), 10.1016/0021-9797(70)90171-2] for electrophoretic mobility when the countercharges lie close to the sphere. Spheres with dipolar and quadrupolar charge distributions rotate and translate as predicted analytically to 4% accuracy or better. We describe how the method can treat general asymmetric shapes and charge distributions. This method offers promise as a way to characterize and manipulate asymmetrically charged colloid-scale objects from biology (e.g., viruses) and technology (e.g., self-assembled clusters).

  10. Asymmetric wettability of nanostructures directs leidenfrost droplets.

    Science.gov (United States)

    Agapov, Rebecca L; Boreyko, Jonathan B; Briggs, Dayrl P; Srijanto, Bernadeta R; Retterer, Scott T; Collier, C Patrick; Lavrik, Nickolay V

    2014-01-28

    Leidenfrost phenomena on nano- and microstructured surfaces are of great importance for increasing control over heat transfer in high power density systems utilizing boiling phenomena. They also provide an elegant means to direct droplet motion in a variety of recently emerging fluidic systems. Here, we report the fabrication and characterization of tilted nanopillar arrays (TNPAs) that exhibit directional Leidenfrost water droplets under dynamic conditions, namely on impact with Weber numbers ≥40 at T ≥ 325 °C. The directionality for these droplets is opposite to the direction previously exhibited by macro- and microscale Leidenfrost ratchets where movement against the tilt of the ratchet was observed. The batch fabrication of the TNPAs was achieved by glancing-angle anisotropic reactive ion etching of a thermally dewet platinum mask, with mean pillar diameters of 100 nm and heights of 200-500 nm. In contrast to previously implemented macro- and microscopic Leidenfrost ratchets, our TNPAs induce no preferential directional movement of Leidenfrost droplets under conditions approaching steady-state film boiling, suggesting that the observed droplet directionality is not a result of the widely accepted mechanism of asymmetric vapor flow. Using high-speed imaging, phase diagrams were constructed for the boiling behavior upon impact for droplets falling onto TNPAs, straight nanopillar arrays, and smooth silicon surfaces. The asymmetric impact and directional trajectory of droplets was exclusive to the TNPAs for impacts corresponding to the transition boiling regime, linking asymmetric surface wettability to preferential directionality of dynamic Leidenfrost droplets on nanostructured surfaces.

  11. Heterogeneous catalytic degradation of polyacrylamide solution | Hu ...

    African Journals Online (AJOL)

    Modified with trace metal elements, the catalytic activity of Fe2O3/Al2O3 could be changed greatly. Among various trace metal elements, Fe2O3/Al2O3 catalysts modified with Co and Cu showed great increase on catalytic activity. International Journal of Engineering, Science and Technology, Vol. 2, No. 7, 2010, pp. 110- ...

  12. Catalytic gasification of dry and wet biomass

    NARCIS (Netherlands)

    van Rossum, G.; Potic, B.; Kersten, Sascha R.A.; van Swaaij, Willibrordus Petrus Maria

    2009-01-01

    Catalytic gasification of dry biomass and of wet biomass streams in hot compressed water are reviewed and discussed as potential technologies for the production of synthesis gas, hydrogen- and methane-rich gas. Next to literature data also new experimental results from our laboratory on catalytic

  13. Integrated catalytic and electrocatalytic conversion of substituted phenols and diaryl ethers

    Energy Technology Data Exchange (ETDEWEB)

    Song, Yang; Chia, Shao H.; Sanyal, Udishnu; Gutierrez, Oliver Y.; Lercher, Johannes A.

    2016-10-17

    Electrocatalytic hydrogenation and catalytic thermal hydrogenation of substituted phenols and diaryl ethers were studied on carbon-supported Rh. For electrocatalytic and catalytic thermal hydrogen addition reactions, the dominant reaction pathway is hydrogenation to cyclic alcohols and cycloalkyl ethers. The presence of substituting methyl or methoxy groups led to lower rates compared to unsubstituted phenol or diphenyl ether. Methoxy or benzyloxy groups, however, undergo C-O bond cleavage via hydrogenolysis and hydrolysis (minor pathway).

  14. Non-catalytic recuperative reformer

    Science.gov (United States)

    Khinkis, Mark J.; Kozlov, Aleksandr P.; Kurek, Harry

    2015-12-22

    A non-catalytic recuperative reformer has a flue gas flow path for conducting hot flue gas from a thermal process and a reforming mixture flow path for conducting a reforming mixture. At least a portion of the reforming mixture flow path is embedded in the flue gas flow path to permit heat transfer from the hot flue gas to the reforming mixture. The reforming mixture flow path contains substantially no material commonly used as a catalyst for reforming hydrocarbon fuel (e.g., nickel oxide, platinum group elements or rhenium), but instead the reforming mixture is reformed into a higher calorific fuel via reactions due to the heat transfer and residence time. In a preferred embodiment, extended surfaces of metal material such as stainless steel or metal alloy that are high in nickel content are included within at least a portion of the reforming mixture flow path.

  15. Electrochemical promotion of catalytic reactions

    Science.gov (United States)

    Imbihl, R.

    2010-05-01

    The electrochemical promotion of heterogeneously catalyzed reactions (EPOC) became feasible through the use of porous metal electrodes interfaced to a solid electrolyte. With the O 2- conducting yttrium stabilized zirconia (YSZ), the Na + conducting β″-Al 2O 3 (β-alumina), and several other types of solid electrolytes the EPOC effect has been demonstrated for about 100 reaction systems in studies conducted mainly in the mbar range. Surface science investigations showed that the physical basis for the EPOC effect lies in the electrochemically induced spillover of oxygen and alkali metal, respectively, onto the surface of the metal electrodes. For the catalytic promotion effect general concepts and mechanistic schemes were proposed but these concepts and schemes are largely speculative. Applying surface analytical tools to EPOC systems the proposed mechanistic schemes can be verified or invalidated. This report summarizes the progress which has been achieved in the mechanistic understanding of the EPOC effect.

  16. Selective catalytic oxidation of ammonia

    Energy Technology Data Exchange (ETDEWEB)

    Leppaelahti, J.; Koljonen, T. [VTT Energy, Espoo (Finland)

    1996-12-31

    In the combustion of fossil fuels, the principal source of nitrogen oxides is nitrogen bound in the fuel structure. In gasification, a large part of fuel nitrogen forms NH{sub 3}, which may form nitrogen oxides during gas combustion. If NH{sub 3} and other nitrogen species could be removed from hot gas, the NO emission could be considerably reduced. However, relatively little attention has been paid to finding new means of removing nitrogen compounds from the hot gasification gas. The possibility of selectively oxidizing NH{sub 3} to N{sub 2} in the hot gasification has been studied at VTT Energy. The largest NH{sub 3} reductions have been achieved by catalytic oxidation on aluminium oxides. (author) (4 refs.)

  17. Gold(I)-Mediated Thiourea Organocatalyst Activation: A Synergic Effect for Asymmetric Catalysis.

    Science.gov (United States)

    Izaga, Anabel; Herrera, Raquel P; Gimeno, M Concepción

    2017-04-07

    Several group 11 metal complexes with chiral thiourea organocatalysts have been prepared and tested as organocatalysts. The promising results on the influence of metal-assisted thiourea organocatalysts in the asymmetric Friedel-Crafts alkylation of indole with nitrostyrene are described. Better results with the metal complexes have been achieved because of the cooperative effects between the chiral thiourea and the metal. The synergic effect between both species is higher than the effect promoted by each one separately, especially for gold(I). These outcomes are attributed to a pioneering gold(I) activation of the thiourea catalysts, affording a more acidic and rigid catalytic complex than that provided by the thiourea alone. Furthermore, the use of the gold-thiourea organocatalyst allows reducing the catalyst loading to 1-3 mol %. This contribution could become an important starting point for further investigations opening a new line of research overlooked so far in the literature.

  18. The evolution of catalytic function

    Science.gov (United States)

    Maurel, Marie-Christine; Ricard, Jacques

    2006-03-01

    It is very likely that the main driving force of enzyme evolution is the requirement to improve catalytic and regulatory efficiency which results from the intrinsic performance as well as from the spatial and functional organization of enzymes in living cells. Kinetic co-operativity may occur in simple monomeric proteins if they display “slow” conformational transitions, at the cost of catalytic efficiency. Oligomeric enzymes on the other hand can be both efficient and co-operative. We speculate that the main reason for the emergence of co-operative oligomeric enzymes is the need for catalysts that are both cooperative and efficient. As it is not useful for an enzyme to respond to a change of substrate concentration in a complex kinetic way, the emergence of symmetry has its probable origin in a requirement for “functional simplicity”. In a living cell, enzyme are associated with other macromolecules and membranes. The fine tuning of their activity may also be reached through mutations of the microenvironment. Our hypothesis is that these mutations are related to the vectorial transport of molecules, to achieve the hysteresis loops of enzyme reactions generated by the coupling of reaction and diffusion, through the co-operativity brought about by electric interactions between a charged substrate and a membrane, and last but not least, through oscillations. As the physical origins of these effects are very simple and do not require complex molecular devices, it is very likely that the functional advantage generated by the spatial and functional organization of enzyme molecules within the cell have appeared in prebiotic catalysis or very early during the primeval stages of biological evolution. We shall began this paper by presenting the nature of the probable earliest catalysts in the RNA world.

  19. Design and optimization of porous ceramic supports for asymmetric ceria-based oxygen transport membranes

    DEFF Research Database (Denmark)

    Kaiser, Andreas; Foghmoes, Søren Preben Vagn; Pećanac, G.

    2016-01-01

    The microstructure, mechanical properties and gas permeability of porous supports of Ce0.9Gd0.1O1.95−δ (CGO) were investigated as a function of sintering temperature and volume fraction of pore former for use in planar asymmetric oxygen transport membranes (OTMs). With increasing the pore former ...... activity of the CGO membrane was reduced by Fe2O3 addition (replacing Co3O4 as sintering additive)....

  20. Asymmetric Reprogramming Capacity of Parental Pronuclei in Mouse Zygotes

    Directory of Open Access Journals (Sweden)

    Wenqiang Liu

    2014-03-01

    Full Text Available It has been demonstrated that reprogramming factors are sequestered in the pronuclei of zygotes after fertilization, because zygotes enucleated at the M phase instead of interphase of the first mitosis can support the development of cloned embryos. However, the contribution of the parental pronucleus derived from either the sperm or the oocyte in reprogramming remains elusive. Here, we demonstrate that the parental pronuclei have asymmetric reprogramming capacities and that the reprogramming factors reside predominantly in the male pronucleus. As a result, only female pronucleus-depleted (FPD mouse zygotes can reprogram somatic cells to a pluripotent state and support the full-term development of cloned embryos; male pronucleus-depleted (MPD zygotes fail to support somatic cell reprogramming. We further demonstrate that fusion of an additional male pronucleus into a zygote greatly enhances reprogramming efficiency. Our data provide a clue to further identify critical reprogramming factors in the male pronucleus.

  1. (A)dS Backgrounds from Asymmetric Orientifolds

    Energy Technology Data Exchange (ETDEWEB)

    Silverstein, Eva M

    2001-07-25

    I present asymmetric orientifold models which, with the addition of RR fluxes, fix all the NS NS moduli including the dilaton. In critical string theory, this gives new AdS backgrounds with (discretely tunably) weak string coupling. Extrapolating to super-critical string theory, this construction leads to a promising candidate for a metastable de Sitter background with string coupling of order 1/10 and dS radius of order 100 times the string scale. Extrapolating further to larger and larger super-critical dimension suggests the possibility of finding de Sitter backgrounds with weaker and weaker string coupling. This note is an updated version of the last part of my Strings 2001 talk.

  2. Asymmetric Return and Volatility Transmission in Conventional and Islamic Equities

    Directory of Open Access Journals (Sweden)

    Zaghum Umar

    2017-03-01

    Full Text Available Abstract: This paper analyses the interdependence between Islamic and conventional equities by taking into consideration the asymmetric effect of return and volatility transmission. We empirically investigate the decoupling hypothesis of Islamic and conventional equities and the potential contagion effect. We analyse the intra-market and inter-market spillover among Islamic and conventional equities across three major markets: the USA, the United Kingdom and Japan. Our sample period ranges from 1996 to 2015. In addition, we segregate our sample period into three sub-periods covering prior to the 2007 financial crisis, the crisis period and the post-crisis period. We find weak support for the decoupling hypothesis during the post-crisis period.

  3. Metal-Dependent Amyloid β-Degrading Catalytic Antibody Construct

    Science.gov (United States)

    Nishiyama, Yasuhiro; Taguchi, Hiroaki; Hara, Mariko; Planque, Stephanie A.; Mitsuda, Yukie; Paul, Sudhir

    2015-01-01

    Catalytic antibodies (catabodies) that degrade target antigens rapidly are rare. We describe the metal-dependence of catabody construct 2E6, an engineered heterodimer of immunoglobulin light chain variable domains that hydrolyzes amyloid β peptides (Aβ) specifically. In addition to the electrophilic phosphonate inhibitor of serine proteases, the metal chelators ethylenediaminetetraacetic acid (EDTA) and 1,10-phenanthroline completely inhibited the hydrolysis of Aβ by catabody 2E6. Formation of catabody-electrophilic phosphonate inhibitor adducts was unaffected by EDTA, suggesting that the metal exerts a favorable effect on a catalytic step after the initial catabody nucleophilic attack on Aβ. The EDTA inactivated catabody failed to disaggregate fibrillar Aβ, indicating the functional importance of the Aβ hydrolytic activity. Treating the EDTA-inactivated catabody with Zn2+ or Co2+ restored the Aβ hydrolytic activity, and Zn2+-induced catabody conformational transitions were evident by fluorescence emission spectroscopy. The studies reveal the absolute catabody dependence on a metal cofactor. PMID:24698848

  4. Catalytic Wittig and aza-Wittig reactions

    Directory of Open Access Journals (Sweden)

    Zhiqi Lao

    2016-11-01

    Full Text Available This review surveys the literature regarding the development of catalytic versions of the Wittig and aza-Wittig reactions. The first section summarizes how arsenic and tellurium-based catalytic Wittig-type reaction systems were developed first due to the relatively easy reduction of the oxides involved. This is followed by a presentation of the current state of the art regarding phosphine-catalyzed Wittig reactions. The second section covers the field of related catalytic aza-Wittig reactions that are catalyzed by both phosphine oxides and phosphines.

  5. Catalytic Wittig and aza-Wittig reactions.

    Science.gov (United States)

    Lao, Zhiqi; Toy, Patrick H

    2016-01-01

    This review surveys the literature regarding the development of catalytic versions of the Wittig and aza-Wittig reactions. The first section summarizes how arsenic and tellurium-based catalytic Wittig-type reaction systems were developed first due to the relatively easy reduction of the oxides involved. This is followed by a presentation of the current state of the art regarding phosphine-catalyzed Wittig reactions. The second section covers the field of related catalytic aza-Wittig reactions that are catalyzed by both phosphine oxides and phosphines.

  6. Observation of asymmetric electromagnetic field profiles in chiral metamaterials

    Science.gov (United States)

    Hisamoto, Nobuyuki; Ueda, Tetsuya; Sawada, Kei; Tomita, Satoshi

    2018-02-01

    We experimentally observe asymmetric electromagnetic field profiles along two-dimensional chiral metamaterials. The asymmetric field profiles depending on the chirality and the operation frequency have been reproduced well by the numerical simulation. Around a chiral meta-atom, distribution of a Poynting vector is found to be shifted asymmetrically. These results are explained in terms of an analogy with the side-jump mechanism in the electronic anomalous Hall systems.

  7. Population dynamics with symmetric and asymmetric harvesting

    Directory of Open Access Journals (Sweden)

    J. Ali

    2009-10-01

    Here $\\lambda, a, b, c$ and $L$ are positive constants with $0asymmetric harvesting case. Our objective is to study the existence of positive solutions and also discuss the effects of harvesting. We will develop appropriate quadrature methods via which we will establish our results.

  8. Asymmetric acoustic transmission in graded beam

    Energy Technology Data Exchange (ETDEWEB)

    Jing, Li, E-mail: lj94172350@hotmail.com [School of Mechanical Engineering and State Key laboratory for Strength and Vibration of Mechanical Structures, Xi’an Jiaotong University, Xi’an, Shaanxi 710049 (China); Wu, Jiu Hui, E-mail: ejhwu@mail.xjtu.edu.cn [School of Mechanical Engineering and State Key laboratory for Strength and Vibration of Mechanical Structures, Xi’an Jiaotong University, Xi’an, Shaanxi 710049 (China); Guan, Dong; Lu, Kuan [School of Mechanical Engineering and State Key laboratory for Strength and Vibration of Mechanical Structures, Xi’an Jiaotong University, Xi’an, Shaanxi 710049 (China); Gao, Nansha [School of Marine Science and Technology, Northwestern Polytechnical University, Xi’an, Shaanxi 710072 (China); Songhua, Cao [School of Mechanical Engineering and State Key laboratory for Strength and Vibration of Mechanical Structures, Xi’an Jiaotong University, Xi’an, Shaanxi 710049 (China)

    2016-12-01

    We demonstrate the dynamic effective material parameters and vibration performance of a graded beam. The structure of the beam was composed of several unit cells with different fill factors. The dispersion relations and energy band structures of each unit cell were calculated using the finite element method (FEM). The dynamic effective material parameters in each unit cell of the graded beam were determined by the dispersion relations and energy band structures. Longitudinal wave propagation was investigated using a numerical method and FEM. The results show that the graded beam allows asymmetric acoustic transmission over a wide range of frequencies.

  9. Asymmetric Laser Radiant Cooling in Storage Rings

    CERN Document Server

    Bulyak, E V; Zimmermann, F

    2011-01-01

    Laser pulses with small spatial and temporal dimensions can interact with a fraction of the electron bunches circulating in Compton storage rings. We studied synchrotron dynamics of such bunches when laser photons scatter off from the electrons with energy higher than the synchronous energy. In this case of ‘asymmetric cooling', as shown theoretically, the stationary energy spread is much smaller than under conditions of regular scattering; the oscillations are damped faster. Coherent oscillations of large amplitude may be damped in one synchrotron period, which makes this method feasible for injection the bunches into a ring in the longitudinal phase space. The theoretical results are validated with simulations.

  10. Asymmetrical transverse structures in nonlinear interferometers

    CERN Document Server

    Romanov, O G

    2003-01-01

    The work presents a novel type of optical instability, which leads to the spontaneous formation of a stationary or pulsating asymmetrical structure in the problem of interaction between two counterpropagating waves in a ring cavity with Kerr-like nonlinearity. Linear stability analysis of interferometer transmission stationary states enabled: (1) to mark out typical bifurcations for this system: self- and cross-modulational instabilities, (2) to determine the range of parameters for which the symmetry breaking of transverse structures and complex temporal behaviour of the light field could be observed. The predictions of linear stability analysis have been verified with numerical modelling of coupled-modes equations.

  11. Electron heating and energy inventory during asymmetric reconnection in a laboratory plasma

    Science.gov (United States)

    Yoo, J.; Na, B.; Jara-Almonte, J.; Yamada, M.; Ji, H.; Roytershteyn, V.; Argall, M. R.; Fox, W.; Chen, L. J.

    2017-12-01

    Electron heating and the energy inventory during asymmetric reconnection are studied in the Magnetic Reconnection Experiment (MRX) [1]. In this plasma, the density ratio is about 8 across the current sheet. Typical features of asymmetric reconnection such as the large density gradients near the low-density-side separatrices, asymmetric in-plane electric field, and bipolar out-of-plane magnetic field are observed. Unlike the symmetric case [2], electrons are also heated near the low-density-side separatrices. The measured parallel electric field may explain the observed electron heating. Although large fluctuations driven by lower-hybrid drift instabilities are also observed near the low-density-side separatrices, laboratory measurements and numerical simulations reported here suggest that they do not play a major role in electron energization. The average electron temperature increase in the exhaust region is proportional to the incoming magnetic energy per an electron/ion pair but exceeds the scaling of the previous space observations [3]. This discrepancy is explained by differences in the boundary condition and system size. The profile of electron energy gain from the electric field shows that there is additional electron energy gain associated with the electron diamagnetic current besides a large energy gain near the X-line. This additional energy gain increases electron enthalpy, not the electron temperature. Finally, a quantitative analysis of the energy inventory during asymmetric reconnection is conducted. Unlike the symmetric case where the ion energy gain is about twice more than the electron energy gain [4], electrons and ions obtain a similar amount of energy during asymmetric reconnection. [1] J. Yoo et al., accepted for a publication in J. Geophys. Res. [2] J. Yoo et al., Phys. Plasmas 21, 055706 (2014). [3] T. Phan et al., Geophys. Res. Lett. 40, 4475 (2013). [4] M. Yamada et al., Nat. Comms. 5, 4474 (2014).

  12. A protic ionic liquid as an atom economical solution for palladium catalyzed asymmetric allylic alkylation.

    Science.gov (United States)

    Guerrero-Ríos, Itzel; Ortiz-Ramírez, Alfonso H; van Leeuwen, Piet W N M; Martin, Erika

    2018-03-12

    The asymmetric allylic alkylation of rac-1,3-diphenyl-3-acetoxyprop-1-ene (I) catalysed by palladium and diverse phosphorus containing ligands [(S)-BINAP, (R,R)-Chiraphite and (R,R)-Et-Duphos] in an ionic liquid [HDBU][OAc] was successfully performed, achieving full conversions and up to 96% ee of the (S)-product when (R,R)-Et-Duphos was used as a ligand. The reaction could be performed using an equimolar amount of substrate, malonate and base DBU, in which case the total products sum to the desired alkylated product and the ionic pair [HDBU][OAc]; this system thus produces its own IL solvent as the only co-product. These catalytic systems were active in recycling experiments for up to four cycles, albeit with a loss of activity due to the poor retention of palladium in the ionic liquid. The catalytic performance of each Pd/ligand system was optimized by varying the ratio of the substrate and malonate. Systems based on [HDBU][OAc] were found to be the best.

  13. Catalytic determination of vanadium in water

    Science.gov (United States)

    Fishman, M. J.; Skougstad, M.W.

    1964-01-01

    A rapid, accurate, and sensitive spectrophotometric method for the quantitative determination of trace amounts of vanadium in water is based on the catalytic effect of vanadium on the rate of oxidation of gallic acid by persulfate in acid solution. Under given conditions of concentrations of reactants, temperature, and reaction time, the extent of oxidation of gallic acid is proportional to the concentration of vanadium present. Vanadium is determined by measuring the absorbance of the sample at 415 m?? and comparison with standard solutions treated in an identical manner. Concentrations in the range of from 0.1 to 8.0 ??g. per liter may be determined with a standard deviation of 0.2 or less. By reducing the reaction time, the method may be extended to cover the range from 1 to 100 ??g. with a standard deviation of 0.8 or less. Several substances interfere, including chloride above 100 p.p.m., and bromide and iodide in much lower concentrations. Interference from the halides is eliminated or minimized by the addition of mercuric nitrate solution. Most other substances do not interfere at the concentration levels at which they commonly occur in natural waters.

  14. Molecular heterogeneous catalysts derived from bipyridine-based organosilica nanotubes for C–H bond activation† †Electronic supplementary information (ESI) available: Experimental details, material characterization data, catalytic measurement details. See DOI: 10.1039/c7sc00713b Click here for additional data file.

    Science.gov (United States)

    Zhang, Shengbo; Wang, Hua; Li, Mei; Han, Jinyu

    2017-01-01

    Heterogeneous metal complex catalysts for direct C–H activation with high activity and durability have always been desired for transforming raw materials into feedstock chemicals. This study described the design and synthesis of one-dimensional organosilica nanotubes containing 2,2′-bipyridine (bpy) ligands in the framework (BPy-NT) and their post-synthetic metalation to provide highly active and robust molecular heterogeneous catalysts. By adjusting the ratios of organosilane precursors, very short BPy-NT with ∼50 nm length could be controllably obtained. The post-synthetic metalation of bipyridine-functionalized nanotubes with [IrCp*Cl(μ-Cl)]2 (Cp* = η5-pentamethylcyclopentadienyl) and [Ir(cod)(OMe)]2 (cod = 1,5-cyclooctadiene) afforded solid catalysts, IrCp*-BPy-NT and Ir(cod)-BPy-NT, which were utilized for C–H oxidation of heterocycles and cycloalkanes as well as C–H borylation of arenes. The cut-short nanotube catalysts displayed enhanced activities and durability as compared to the analogous homogeneous catalysts and other conventional heterogeneous catalysts, benefiting from the isolated active sites as well as the fast transport of substrates and products. After the reactions, a detailed characterization of Ir-immobilized BPy-NT via TEM, SEM, nitrogen adsorption, UV/vis, XPS, and 13C CP MAS NMR indicated the molecular nature of the active species as well as stable structures of nanotube scaffolds. This study demonstrates the potential of BPy-NT with a short length as an integration platform for the construction of efficient heterogeneous catalytic systems for organic transformations. PMID:28970878

  15. Novel asymmetric chitosan/PVP/nanocellulose wound dressing: In vitro and in vivo evaluation.

    Science.gov (United States)

    Poonguzhali, R; Khaleel Basha, S; Sugantha Kumari, V

    2018-06-01

    The present study was to develop a novel chitosan based symmetric and asymmetric bionanocomposite for potential wound dressing application. Chitosan (C)/Poly (vinyl pyrrolidone) (P)/nanocellulose (NC) membrane were fabricated by salt leaching method with the addition of 3% and 5% wt of nanocellulose. To obtain asymmetric material one side of the membrane was coated by stearic acid (S) which could form hydrophobic surface and another side acts as a hydrophilic surface. Nanocellulose of size 2-10nm was synthesized and characterized by TEM analysis. SEM showed the hydrophilic surface of asymmetric bionanocomposite consists of porous structure and hydrophobic surface is smooth and homogeneous. The results revealed that the Chitosan/PVP/Nanocellulose 3%-Stearic acid (CPNC3%-S) had a moderate swelling ratio, porosity, barrier and mechanical properties. Incorporation of nanocellulose into chitosan/PVP matrix could enhance the antibacterial activity. The hydrophobic surface of the CPNC3%-S bionanocomposite shows water repellent and antiadhesion properties towards E. coli bacteria and also the hydrophilic surface exhibit excellent antibacterial property and cytotoxicity towards bacterial pathogens. In vivo wound healing test shows better re-epithelialization and wound contraction compared with control and Chitosan/PVP-stearic acid (CP-S) bionanocomposite. Asymmetric bionanocomposite Chitosan/PVP/Nanocellulose coated with 3%-Stearic acid (CPNC3%-S) exhibited very good invitro cytocompatibility and enabled a faster wound healing than symmetric dressing, hence showing great potential to be applied as wound dressings. Copyright © 2018 Elsevier B.V. All rights reserved.

  16. Auxin as an inducer of asymmetrical division generating the subsidiary cells in stomatal complexes of Zea mays.

    Science.gov (United States)

    Livanos, Pantelis; Giannoutsou, Eleni; Apostolakos, Panagiotis; Galatis, Basil

    2015-01-01

    The data presented in this work revealed that in Zea mays the exogenously added auxins indole-3-acetic acid (IAA) and 1-napthaleneacetic acid (NAA), promoted the establishment of subsidiary cell mother cell (SMC) polarity and the subsequent subsidiary cell formation, while treatment with auxin transport inhibitors 2,3,5-triiodobenzoic acid (TIBA) and 1-napthoxyacetic acid (NOA) specifically blocked SMC polarization and asymmetrical division. Furthermore, in young guard cell mother cells (GMCs) the PIN1 auxin efflux carriers were mainly localized in the transverse GMC faces, while in the advanced GMCs they appeared both in the transverse and the lateral ones adjacent to SMCs. Considering that phosphatidyl-inositol-3-kinase (PI3K) is an active component of auxin signal transduction and that phospholipid signaling contributes in the establishment of polarity, treatments with the specific inhibitor of the PI3K LY294002 were carried out. The presence of LY294002 suppressed polarization of SMCs and prevented their asymmetrical division, whereas combined treatment with exogenously added NAA and LY294002 restricted the promotional auxin influence on subsidiary cell formation. These findings support the view that auxin is involved in Z. mays subsidiary cell formation, probably functioning as inducer of the asymmetrical SMC division. Collectively, the results obtained from treatments with auxin transport inhibitors and the appearance of PIN1 proteins in the lateral GMC faces indicate a local transfer of auxin from GMCs to SMCs. Moreover, auxin signal transduction seems to be mediated by the catalytic function of PI3K.

  17. Catalytic partial oxidation of pyrolysis oils

    Science.gov (United States)

    Rennard, David Carl

    2009-12-01

    details the catalytic partial oxidation of glycerol without preheat: droplets of glycerol are sprayed directly onto the top of the catalyst bed, where they react autothermally with contact times on the order of tau ≈ 30 ms. The reactive flash volatilization of glycerol results in equilibrium syngas production over Rh-Ce catalysts. In addition, water can be added to the liquid glycerol, resulting in true autothermal reforming. This highly efficient process can increase H2 yields and alter the H2 to CO ratio, allowing for flexibility in syngas quality depending on the purpose. Chapter 5 details the results of a time on stream experiment, in which optimal syngas conditions are chosen. Although conversion is 100% for 450 hours, these experiments demonstrate the deactivation of the catalyst over time. Deactivation is exhibited by decreases in H2 and CO 2 production accompanied by a steady increase in CO and temperature. These results are explained as a loss of water-gas shift equilibration. SEM images suggest catalyst sintering may play a role; EDS indicates the presence of impurities on the catalyst. In addition, the instability of quartz in the reactor is demonstrated by etching, resulting in a hole in the reactor tube at the end of the experiment. These results suggest prevaporization may be desirable in this application, and that quartz is not a suitable material for the reactive flash volatilization of oxygenated fuels. In Chapter 6, pyrolysis oil samples from three sources - poplar, pine, and hardwoods - are explored in the context of catalytic partial oxidation. Lessons derived from the tests with model compounds are applied to reactor design, resulting in the reactive flash vaporization of bio oils. Syngas is successfully produced, though deactivation due to coke and ash deposition keeps H2 below equlibrium. Coke formation is observed on the reactor walls, but is avoided between the fuel injection site and catalyst by increasing the proximity of these in the reactor

  18. Evolutionary stability in the asymmetric volunteer's dilemma.

    Directory of Open Access Journals (Sweden)

    Jun-Zhou He

    Full Text Available It is often assumed that in public goods games, contributors are either strong or weak players and each individual has an equal probability of exhibiting cooperation. It is difficult to explain why the public good is produced by strong individuals in some cooperation systems, and by weak individuals in others. Viewing the asymmetric volunteer's dilemma game as an evolutionary game, we find that whether the strong or the weak players produce the public good depends on the initial condition (i.e., phenotype or initial strategy of individuals. These different evolutionarily stable strategies (ESS associated with different initial conditions, can be interpreted as the production modes of public goods of different cooperation systems. A further analysis revealed that the strong player adopts a pure strategy but mixed strategies for the weak players to produce the public good, and that the probability of volunteering by weak players decreases with increasing group size or decreasing cost-benefit ratio. Our model shows that the defection probability of a "strong" player is greater than the "weak" players in the model of Diekmann (1993. This contradicts Selten's (1980 model that public goods can only be produced by a strong player, is not an evolutionarily stable strategy, and will therefore disappear over evolutionary time. Our public good model with ESS has thus extended previous interpretations that the public good can only be produced by strong players in an asymmetric game.

  19. An asymmetric B factory based on PEP

    International Nuclear Information System (INIS)

    1991-02-01

    In this report we describe a design for a high-luminosity Asymmetric B Factory to be built in the PEP tunnel on the SLAC site. This proposal, a collaborative effort SLAC, LBL, and LLNL, is the culmination of more than two years of effort aimed at the design and construction of an asymmetric e + e - collider capable of achieving a luminosity of L = 3 x 10 33 cm -2 s -1 . The configuration adopted utilizes two storage rings, and electron ring operating at 9 GeV and a positron ring at 3.1 GeV, each with a circumference of 2200 m. The high-energy ring is an upgrade of the PEP storage ring at SLAC; all PEP magnets and most power supplies will be reused. The upgrade consists primarily of replacing the PEP vacuum chamber and RF system with newly designed versions optimized for the high-current environment of the B Factory. The low-energy ring will be newly constructed and will be situated atop the high-energy ring in the PEP tunnel. Utilities already installed in the PEP tunnel are largely sufficient to operate the two B Factory storage rings

  20. Asymmetric inheritance of cytoophidia in Schizosaccharomyces pombe

    Directory of Open Access Journals (Sweden)

    Jing Zhang

    2014-10-01

    Full Text Available A general view is that Schizosaccharomyces pombe undergoes symmetric cell division with two daughter cells inheriting equal shares of the content from the mother cell. Here we show that CTP synthase, a metabolic enzyme responsible for the de novo synthesis of the nucleotide CTP, can form filamentous cytoophidia in the cytoplasm and nucleus of S. pombe cells. Surprisingly, we observe that both cytoplasmic and nuclear cytoophidia are asymmetrically inherited during cell division. Our time-lapse studies suggest that cytoophidia are dynamic. Once the mother cell divides, the cytoplasmic and nuclear cytoophidia independently partition into one of the two daughter cells. Although the two daughter cells differ from one another morphologically, they possess similar chances of inheriting the cytoplasmic cytoophidium from the mother cell, suggesting that the partition of cytoophidium is a stochastic process. Our findings on asymmetric inheritance of cytoophidia in S. pombe offer an exciting opportunity to study the inheritance of metabolic enzymes in a well-studied model system.

  1. Asymmetric disassembly and robustness in declining networks

    Science.gov (United States)

    Saavedra, Serguei; Reed-Tsochas, Felix; Uzzi, Brian

    2008-01-01

    Mechanisms that enable declining networks to avert structural collapse and performance degradation are not well understood. This knowledge gap reflects a shortage of data on declining networks and an emphasis on models of network growth. Analyzing >700,000 transactions between firms in the New York garment industry over 19 years, we tracked this network's decline and measured how its topology and global performance evolved. We find that favoring asymmetric (disassortative) links is key to preserving the topology and functionality of the declining network. Based on our findings, we tested a model of network decline that combines an asymmetric disassembly process for contraction with a preferential attachment process for regrowth. Our simulation results indicate that the model can explain robustness under decline even if the total population of nodes contracts by more than an order of magnitude, in line with our observations for the empirical network. These findings suggest that disassembly mechanisms are not simply assembly mechanisms in reverse and that our model is relevant to understanding the process of decline and collapse in a broad range of biological, technological, and financial networks. PMID:18936489

  2. D mesons in asymmetric nuclear matter

    International Nuclear Information System (INIS)

    Mishra, Amruta; Mazumdar, Arindam

    2009-01-01

    We calculate the in-medium D and D meson masses in isospin-asymmetric nuclear matter in an effective chiral model. The D and D mass modifications arising from their interactions with the nucleons and the scalar mesons in the effective hadronic model are seen to be appreciable at high densities and have a strong isospin dependence. These mass modifications can open the channels of the decay of the charmonium states (Ψ ' ,χ c ,J/Ψ) to DD pairs in dense hadronic matter. The isospin asymmetry in the doublet D=(D 0 ,D + ) is seen to be particularly appreciable at high densities and should show in observables such as their production and flow in asymmetric heavy-ion collisions in the compressed baryonic matter experiments in the future facility of FAIR, GSI. The results of the present work are compared to calculations of the D(D) in-medium masses in the literature using the QCD sum rule approach, quark meson coupling model, and coupled channel approach as well as to those from studies of quarkonium dissociation using heavy-quark potentials from lattice QCD at finite temperatures

  3. Asymmetric Cell Divisions in the Epidermis

    Science.gov (United States)

    Poulson, Nicholas D.; Lechler, Terry

    2012-01-01

    Generation of three-dimensional tissue with distinct cell types is required for the development of all organs. On its own, mitotic spindle orientation allows tissues to change in length or shape. In combination with intrinsic or extrinsic cues this can also be coupled to the generation of diverse cell fates - a process known as asymmetric cell division (ACD). Understanding ACD’s has been greatly aided by studies in invertebrate model systems, where genetics and live imaging have provided the basis for much of what we know. ACD’s also drive the development and differentiation of the epidermis in mammals. While similar to the invertebrate models, the epidermis is distinct in balancing symmetric and asymmetric divisions to yield a tissue of the correct surface area and thickness. Here we review the roles of spindle orientation in driving both morphogenesis and cell fate decisions. We highlight the epidermis as a unique model system to study not only basic mechanisms of ACD, but also to study their regulation during development. PMID:22449491

  4. Asymmetric facial skin viscoelasticity during climacteric aging

    Science.gov (United States)

    Piérard, Gérald E; Hermanns-Lê, Trinh; Gaspard, Ulysse; Piérard-Franchimont, Claudine

    2014-01-01

    Background Climacteric skin aging affects certain biophysical characteristics of facial skin. The purpose of the present study was to assess the symmetric involvement of the cheeks in this stage of the aging process. Methods Skin viscoelasticity was compared on both cheeks in premenopausal and post-menopausal women with indoor occupational activities somewhat limiting the influence of chronic sun exposure. Eighty-four healthy women comprising 36 premenopausal women and 48 early post-menopausal women off hormone replacement therapy were enrolled in two groups. The tensile characteristics of both cheeks were tested and compared in each group. A computerized suction device equipped with a 2 mm diameter hollow probe was used to derive viscoelasticity parameters during a five-cycle procedure of 2 seconds each. Skin unfolding, intrinsic distensibility, biological elasticity, and creep extension were measured. Results Both biological elasticity and creep extension were asymmetric on the cheeks of the post-menopausal women. In contrast, these differences were more discrete in the premenopausal women. Conclusion Facial skin viscoelasticity appeared to be asymmetric following menopause. The possibility of asymmetry should be taken into account in future studies of the effects of hormone replacement therapy and any antiaging procedure on the face in menopausal women. PMID:24748810

  5. Asymmetric DSL Technology of Signal Transmission

    Directory of Open Access Journals (Sweden)

    Dražen Kovačević

    2005-05-01

    Full Text Available Asymmetric flow of information is the key feature of theADSL (Asymmetric Digital Subscriber Loop technology, i.e.higher data transmission rate towards the user than from theuser towards the network. Characteristic is the short messagesending by the user with a certain request to the se!Ver. These!Ver responds to the request by a significantly longer messageof various electronic forms (data, digitized speech, pictures orvideo. Therefore, this technology is most often used by smalland medium users. ADSL is currently the only commerciallyavailable DSL technology which is still experiencing the breakthroughon the seiVice market. It enables faster access to theInternet, LAN (Local Area Network, videoconferencing, VoD(Video on Demand and interactive multimedia. In order tostandardize such se/Vices, the !TU (International TelecommunicationsUnion G. 992.1 (standardized DMT-discrete multi-tone line coding technology and ANSJ (American NationalStandards Institution Tl.413-95!98 are used for ADSL. DMT(Discrete Multi Tone, as the more popular one, uses the linecoding technique, which splits a certain frequency range intoseveral sub-channels. Most of these sub-channels are used forupstream and downstream transmission of speech and data,whereas some are used as pilot signals or kept in rese/Ve. Suchmodulation technique expands the frequency spectrum, allowingthe usage ofbroadband se/Vices per one pair of wires. In thisway the sharing of speech and data se/Vice transmission is realized.

  6. MOBILE COMPLEX FOR CATALYTIC THERMAL WASTE TREATMENT

    Directory of Open Access Journals (Sweden)

    Vedi V.E.

    2012-12-01

    Full Text Available The design and purpose of the basic units of the mobile waste processing complex “MPK” are described. Experimental data of catalytic purification of exhaust gases are presented. Experimental data on catalytic clearing of final gases of a designed mobile incinerator plant are shown. It is defined, that concentrating of parasitic bridging in waste gases of the complex are considerably smaller, rather than allowed by normative documents.

  7. Catalytic Conversion of Cellulose to Levulinic Acid by Metal Chlorides

    Directory of Open Access Journals (Sweden)

    Beixiao Zhang

    2010-08-01

    Full Text Available The catalytic performance of various metal chlorides in the conversion of cellulose to levulinic acid in liquid water at high temperatures was investigated. The effects of reaction parameters on the yield of levulinic acid were also explored. The results showed that alkali and alkaline earth metal chlorides were not effective in conversion of cellulose, while transition metal chlorides, especially CrCl3, FeCl3 and CuCl2 and a group IIIA metal chloride (AlCl3, exhibited high catalytic activity. The catalytic performance was correlated with the acidity of the reaction system due to the addition of the metal chlorides, but more dependent on the type of metal chloride. Among those metal chlorides, chromium chloride was found to be exceptionally effective for the conversion of cellulose to levulinic acid, affording an optimum yield of 67 mol % after a reaction time of 180 min, at 200 °C, with a catalyst dosage of 0.02 M and substrate concentration of 50 wt %. Chromium metal, most of which was present in its oxide form in the solid sample and only a small part in solution as Cr3+ ion, can be easily separated from the resulting product mixture and recycled. Finally, a plausible reaction scheme for the chromium chloride catalyzed conversion of cellulose in water was proposed.

  8. Catalytic conversion of cellulose to levulinic acid by metal chlorides.

    Science.gov (United States)

    Peng, Lincai; Lin, Lu; Zhang, Junhua; Zhuang, Junping; Zhang, Beixiao; Gong, Yan

    2010-08-02

    The catalytic performance of various metal chlorides in the conversion of cellulose to levulinic acid in liquid water at high temperatures was investigated. The effects of reaction parameters on the yield of levulinic acid were also explored. The results showed that alkali and alkaline earth metal chlorides were not effective in conversion of cellulose, while transition metal chlorides, especially CrCl(3), FeCl(3) and CuCl(2) and a group IIIA metal chloride (AlCl(3)), exhibited high catalytic activity. The catalytic performance was correlated with the acidity of the reaction system due to the addition of the metal chlorides, but more dependent on the type of metal chloride. Among those metal chlorides, chromium chloride was found to be exceptionally effective for the conversion of cellulose to levulinic acid, affording an optimum yield of 67 mol % after a reaction time of 180 min, at 200 degrees C, with a catalyst dosage of 0.02 M and substrate concentration of 50 wt %. Chromium metal, most of which was present in its oxide form in the solid sample and only a small part in solution as Cr3+ ion, can be easily separated from the resulting product mixture and recycled. Finally, a plausible reaction scheme for the chromium chloride catalyzed conversion of cellulose in water was proposed.

  9. Recyclable Nanostructured Catalytic Systems in Modern Environmentally Friendly Organic Synthesis

    Directory of Open Access Journals (Sweden)

    Irina Beletskaya

    2010-07-01

    Full Text Available Modern chemical synthesis makes heavy use of different types of catalytic systems: homogeneous, heterogeneous and nano-sized. The latter – nano-sized catalysts – have given rise in the 21st century to a rapidly developing area of research encompassing several prospects and opportunities for new technologies. Catalytic reactions ensure high regio- and stereoselectivity of chemical transformations, as well as better yields and milder reaction conditions. In recent years several novel catalytic systems were developed for selective formation of carbon-heteroatom and carbon-carbon bonds. This review presents the achievements of our team in our studies on various types of catalysts containing metal nanoparticles: palladium-containing diblock copolymer micelles; soluble palladium-containing polymers; metallides on a support; polymeric metal salts and oxides; and, in addition, metal-free organic catalysts based on soluble polymers acting as nanoreactors. Representative examples are given and discussed in light of possible applications to solve important problems in modern organic synthesis.

  10. Ants exhibit asymmetric hybridization in a mosaic hybrid zone.

    Science.gov (United States)

    Purcell, Jessica; Zahnd, Sacha; Athanasiades, Anouk; Türler, Rebecca; Chapuisat, Michel; Brelsford, Alan

    2016-10-01

    Research on hybridization between species provides unparalleled insights into the pre- and postzygotic isolating mechanisms that drive speciation. In social organisms, colony-level incompatibilities may provide additional reproductive barriers not present in solitary species, and hybrid zones offer an opportunity to identify these barriers. Here, we use genotyping-by-sequencing to sequence hundreds of markers in a hybrid zone between two socially polymorphic ant species, Formica selysi and Formica cinerea. We characterize the zone, determine the frequency of hybrid workers, infer whether hybrid queens or males are produced and investigate whether hybridization is influenced by colony social organization. We also compare cuticular hydrocarbon profiles and aggression levels between the two species. The hybrid zone exhibits a mosaic structure. The asymmetric distribution of hybrids skewed towards F. cinerea suggests a pattern of unidirectional nuclear gene flow from F. selysi into F. cinerea. The occurrence of backcrossed individuals indicates that hybrid queens and/or males are fertile, and the presence of the F. cinerea mitochondrial haplotype in 97% of hybrids shows that successful F1 hybrids will generally have F. cinerea mothers and F. selysi fathers. We found no evidence that social organization contributes to speciation, because hybrids occur in both single-queen and multiple-queen colonies. Strongly differentiated cuticular hydrocarbon profiles and heightened interspecific aggression further reveal that species recognition cues are both present and perceived. The discovery of fertile hybrids and asymmetrical gene flow is unusual in ants, and this hybrid zone will therefore provide an ideal system with which to investigate speciation in social insects. © 2016 John Wiley & Sons Ltd.

  11. Hydrogen mitigation by catalytic recombiners and ignition during severe accidents

    International Nuclear Information System (INIS)

    Rohde, J.; Chakraborty, A.K.; Heitsch, M.; Klein-Hebling, W.

    1994-01-01

    A large amount of hydrogen is expected to be released within a large dry containment of a PWR shortly after the onset of a severe accident, leading to core melting. According to local gas concentrations, turbulence and structural configurations within the containment, the released hydrogen can reach the boundary of deflagration or under certain conditions cause local detonations threatening the containment integrity. During the last few years, several concepts of mitigation have been developed to limit the hydrogen concentrations and extensive efforts have been given to investigate the use of catalytic recombiners as well as the use of deliberate ignition within the contemplated framework of a 'Dual-concept'. Although the recent recommendation of the German Reactor Safety Commission (RSK) foresees the sole application of catalytic recombiners to remove hydrogen during severe accident, a review is planned within two years for the partial and directed additional application of early ignitions or post dilution of the atmosphere of the compartments in conjunction with the recombiners installed. This presentation will review the results of large number of experiments performed both in small scale and large scale to qualify the recombiners. It is also the subject of the presentation to address the requirements for proper and secure functioning of the catalyzers under the existing boundary conditions during the severe accidents. These requirements ask for measures, starting from the proper selection of catalysts, multi purposed catalytic devices and their protection against contamination during the standby condition as well as against aerosol deposition and surface poisoning during the propagation of an accident. A short review of the results to large scale experiments with the combined application of catalytic devices and igniters form also a part of this presentation. (author). 8 refs., 2 tabs., 7 figs

  12. Quantum Molecular Interaction Field Models of Substrate Enantioselection in Asymmetric Processes.

    Science.gov (United States)

    Kozlowski, Marisa C; Ianni, James C

    2010-06-01

    Computational models correlating substrate structure to enantioselection with asymmetric catalysts using the QMQSAR program are described. In addition to rapidly providing predictions that could be used to facilitate the screening of catalysts for novel substrates, the QMQSAR program identifies the portions of the substrate that most directly influence the enantioselectivity. The lack underlying relationship between all the substrates in one case, requires two quantitative structure selectivity relationships (QSSR) models to describe all of the experimental results.

  13. alpha-Ketophosphonates as ester surrogates : isothiourea-catalyzed asymmetric diester and lactone synthesis

    OpenAIRE

    Smith, Siobhan R.; Leckie, Stuart M.; Holmes, Reuben; Douglas, James; Fallan, Charlene; Shapland, Peter; Pryde, David; Slawin, Alexandra M. Z.; Smith, Andrew D.

    2014-01-01

    This work is in part supported by the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007-2013) ERC Grant Agreement No. 279850 Isothiourea HBTM-2.1 catalyzes the asymmetric Michael addition/lactonization of aryl- and alkenylacetic acids using α-keto-β,γ-unsaturated phosphonates as α,β-unsaturated ester surrogates, giving access to a diverse range of stereodefined lactones or enantioenriched functionalized diesters upon ring-opening. Postprint Pe...

  14. Asymmetric synthesis of (-)-sedacryptine through a diastereoselective Mannich reaction of N,O-acetals with ketones.

    Science.gov (United States)

    Liu, Yi-Wen; Ma, Rui-Jun; Yan, Jia-Hang; Zhou, Zhu; Wei, Bang-Guo

    2018-01-31

    An efficient diastereoselective approach to access the 3-hydroxy-2,6-disubstituted piperidine scaffold 1 has been developed through the Mannich process involving N,O-acetal (2S,3R)-6 and ketones in excellent yield with high diastereoselectivity (dr > 99 : 1). In addition, the utility of this convenient one-pot process is demonstrated by the asymmetric synthesis of (-)-sedacryptine 3.

  15. Application of a new amidophosphite ligand to Rh-catalyzed asymmetric hydrogenation of β-dehydroamino acid derivatives in supercritical carbon dioxide: activation effect of protic Co-solvents.

    Science.gov (United States)

    Lyubimov, Sergey E; Rastorguev, Eugenie A; Davankov, Vadim A

    2011-09-01

    New chiral amidophosphite ligand was synthesized and tested in the Rh-catalyzed asymmetric hydrogenation of (Z)-β-(acylamino)acrylates in protic solvents and supercritical carbon dioxide (scCO(2) ) The catalytic performance is affected greatly by the acidity of the solvents. Better enantioselectivity (up to 88% ee) was achieved in scCO(2) containing 1,1,1,3,3,3-hexafluoro-2-propanol, compared to neat protic solvents. Copyright © 2011 Wiley-Liss, Inc.

  16. Preparation of chiral-at-metal catalysts and their use in asymmetric photoredox chemistry.

    Science.gov (United States)

    Ma, Jiajia; Zhang, Xiao; Huang, Xiaoqiang; Luo, Shipeng; Meggers, Eric

    2018-04-01

    Asymmetric catalysis is a powerful approach for the synthesis of optically active compounds, and visible light constitutes an abundant source of energy to enable chemical transformations, which are often triggered by photoinduced electron transfer (photoredox chemistry). Recently, bis-cyclometalated iridium(III) and rhodium(III) complexes were introduced as a novel class of catalysts for combining asymmetric catalysis with visible-light-induced photoredox chemistry. These catalysts are attractive because of their unusual feature of chirality originating exclusively from a stereogenic metal center, which offers the prospect of an especially effective asymmetric induction upon direct coordination of the substrate to the metal center. As these chiral catalysts contain only achiral ligands, special strategies are required for their synthesis. In this protocol, we describe strategies for preparing two types of chiral-at-metal catalysts, namely the Λ- and Δ-enantiomers (left- and right-handed propellers, respectively) of the iridium complex IrS and the rhodium complex RhS. Both contain two cyclometalating 5-tert-butyl-2-phenylbenzothiazoles in addition to two acetonitrile ligands and a hexafluorophosphate counterion. The two cyclometalated ligands set the propeller-shaped chiral geometry, but the acetonitriles are labile and can be replaced by substrate molecules. The synthesis protocol consists of three stages: first, preparation of the ligand 5-tert-butyl-2-phenylbenzothiazole; second, preparation of salicylthiazoline (used for iridium) and salicyloxazoline (used for rhodium) chiral auxiliaries; and third, the auxiliary-mediated synthesis of the individual enantiopure Λ- and Δ-configured catalysts. This class of stereogenic-only-at-metal complexes is of substantial value in the field of asymmetric catalysis, offering stereocontrolled radical reactions based on visible-light-activated photoredox chemistry. Representative examples of visible-light-induced asymmetric

  17. Adsorbent catalytic nanoparticles and methods of using the same

    Energy Technology Data Exchange (ETDEWEB)

    Slowing, Igor Ivan; Kandel, Kapil

    2017-01-31

    The present invention provides an adsorbent catalytic nanoparticle including a mesoporous silica nanoparticle having at least one adsorbent functional group bound thereto. The adsorbent catalytic nanoparticle also includes at least one catalytic material. In various embodiments, the present invention provides methods of using and making the adsorbent catalytic nanoparticles. In some examples, the adsorbent catalytic nanoparticles can be used to selectively remove fatty acids from feedstocks for biodiesel, and to hydrotreat the separated fatty acids.

  18. Gaze-Stabilizing Central Vestibular Neurons Project Asymmetrically to Extraocular Motoneuron Pools.

    Science.gov (United States)

    Schoppik, David; Bianco, Isaac H; Prober, David A; Douglass, Adam D; Robson, Drew N; Li, Jennifer M B; Greenwood, Joel S F; Soucy, Edward; Engert, Florian; Schier, Alexander F

    2017-11-22

    Within reflex circuits, specific anatomical projections allow central neurons to relay sensations to effectors that generate movements. A major challenge is to relate anatomical features of central neural populations, such as asymmetric connectivity, to the computations the populations perform. To address this problem, we mapped the anatomy, modeled the function, and discovered a new behavioral role for a genetically defined population of central vestibular neurons in rhombomeres 5-7 of larval zebrafish. First, we found that neurons within this central population project preferentially to motoneurons that move the eyes downward. Concordantly, when the entire population of asymmetrically projecting neurons was stimulated collectively, only downward eye rotations were observed, demonstrating a functional correlate of the anatomical bias. When these neurons are ablated, fish failed to rotate their eyes following either nose-up or nose-down body tilts. This asymmetrically projecting central population thus participates in both upward and downward gaze stabilization. In addition to projecting to motoneurons, central vestibular neurons also receive direct sensory input from peripheral afferents. To infer whether asymmetric projections can facilitate sensory encoding or motor output, we modeled differentially projecting sets of central vestibular neurons. Whereas motor command strength was independent of projection allocation, asymmetric projections enabled more accurate representation of nose-up stimuli. The model shows how asymmetric connectivity could enhance the representation of imbalance during nose-up postures while preserving gaze stabilization performance. Finally, we found that central vestibular neurons were necessary for a vital behavior requiring maintenance of a nose-up posture: swim bladder inflation. These observations suggest that asymmetric connectivity in the vestibular system facilitates representation of ethologically relevant stimuli without

  19. Homogenous Pd-catalyzed asymmetric hydrogenation of unprotected indoles: scope and mechanistic studies.

    Science.gov (United States)

    Duan, Ying; Li, Lu; Chen, Mu-Wang; Yu, Chang-Bin; Fan, Hong-Jun; Zhou, Yong-Gui

    2014-05-28

    An efficient palladium-catalyzed asymmetric hydrogenation of a variety of unprotected indoles has been developed that gives up to 98% ee using a strong Brønsted acid as the activator. This methodology was applied in the facile synthesis of biologically active products containing a chiral indoline skeleton. The mechanism of Pd-catalyzed asymmetric hydrogenation was investigated as well. Isotope-labeling reactions and ESI-HRMS proved that an iminium salt formed by protonation of the C═C bond of indoles was the significant intermediate in this reaction. The important proposed active catalytic Pd-H species was observed with (1)H NMR spectroscopy. It was found that proton exchange between the Pd-H active species and solvent trifluoroethanol (TFE) did not occur, although this proton exchange had been previously observed between metal hydrides and alcoholic solvents. Density functional theory calculations were also carried out to give further insight into the mechanism of Pd-catalyzed asymmetric hydrogenation of indoles. This combination of experimental and theoretical studies suggests that Pd-catalyzed hydrogenation goes through a stepwise outer-sphere and ionic hydrogenation mechanism. The activation of hydrogen gas is a heterolytic process assisted by trifluoroacetate of Pd complex via a six-membered-ring transition state. The reaction proceeds well in polar solvent TFE owing to its ability to stabilize the ionic intermediates in the Pd-H generation step. The strong Brønsted acid activator can remarkably decrease the energy barrier for both Pd-H generation and hydrogenation. The high enantioselectivity arises from a hydrogen-bonding interaction between N-H of the iminium salt and oxygen of the coordinated trifluoroacetate in the eight-membered-ring transition state for hydride transfer, while the active chiral Pd complex is a typical bifunctional catalyst, effecting both the hydrogenation and hydrogen-bonding interaction between the iminium salt and the coordinated

  20. Catalytic decomposition of N2O on ordered crystalline metal oxides.

    Science.gov (United States)

    Ma, Zhen; Ren, Yu; Lu, Yanbin; Bruce, Peter G

    2013-07-01

    The synthesis of mesoporous metal oxides using mesoporous silicas or carbons as hard templates has attracted growing interest recently, but the catalytic application of mesoporous metal oxides has not been studied sufficiently. In addition, few publications have compared the catalytic performance of a series of mesoporous metal oxides in the same reaction, and little is known about the influence of preparation details of mesoporous metal oxides on catalytic activity. Herein, ordered crystalline mesoporous metal oxides (i.e., CeO2, Co3O4, Cr2O3, CuO, alpha-Fe2O3, beta-MnO2, Mn2O3, Mn3O4, NiO) prepared using mesoporous SiO2 (KIT-6) as a hard template were tested in the decomposition of N2O, an environmental pollutant, and the catalytic performance was compared with that of commercial metal oxides with low surface areas. In particular, mesoporous Co3O4, beta-MnO2, and NiO showed high N2O conversions at 350 degrees C. The influence of preparation parameters of mesoporous Co3O4 on catalytic activity was then studied in more detail. Mesoporous Co3O4 samples with different pore sizes and wall thicknesses were prepared using KIT-6 synthesized under different hydrothermal or calcination temperatures. Interestingly, the catalytic activities of different mesoporous Co3O4 samples were found to be influenced by these preparation details.

  1. Rapid asymmetrical evolution of Saccharomyces cerevisiae wine yeasts.

    Science.gov (United States)

    Ambrona, Jesús; Vinagre, Antonia; Ramírez, Manuel

    2005-12-01

    Genetic instability causes very rapid asymmetrical loss of heterozygosity (LOH) at the cyh2 locus and loss of killer K2 phenotype in some wine yeasts under the usual laboratory propagation conditions or after long freeze-storage. The direction of this asymmetrical evolution in heterozygous cyh2(R)/CYH2(S) hybrids is determined by the mechanism of asymmetrical LOH. However, the speed of the process is affected by the differences in cell viability between the new homozygous yeasts and the original heterozygous hybrid cells. The concomitant loss of ScV-M2 virus in the LOH process may increase cell viability of cyh2(R)/cyh2(R) yeasts and so favour asymmetrical evolution. The presence of active killer K2 toxin, however, abolishes the asymmetrical evolution of the hybrid populations. This phenomenon may cause important sudden phenotype changes in industrial and pathogenic yeasts. Copyright 2005 John Wiley & Sons, Ltd.

  2. Subcopula-based measure of asymmetric association for contingency tables.

    Science.gov (United States)

    Wei, Zheng; Kim, Daeyoung

    2017-10-30

    For the analysis of a two-way contingency table, a new asymmetric association measure is developed. The proposed method uses the subcopula-based regression between the discrete variables to measure the asymmetric predictive powers of the variables of interest. Unlike the existing measures of asymmetric association, the subcopula-based measure is insensitive to the number of categories in a variable, and thus, the magnitude of the proposed measure can be interpreted as the degree of asymmetric association in the contingency table. The theoretical properties of the proposed subcopula-based asymmetric association measure are investigated. We illustrate the performance and advantages of the proposed measure using simulation studies and real data examples. Copyright © 2017 John Wiley & Sons, Ltd.

  3. Behavior of forced asymmetric oscillators at resonance

    Directory of Open Access Journals (Sweden)

    C. Fabry

    2000-12-01

    Full Text Available This article collects recent results concerning the behavior at resonance of forced oscillators driven by an asymmetric restoring force, with or without damping. This synthesis emphasizes the key role played by a function denoted by $Phi_{alpha,eta,p}$, which is, up to a sign reversal of its argument, a correlation product of the forcing term $p$ and of a function representing a free oscillation for theundamped equation. The theoretical results are accompanied by graphical representations illustrating the behavior of the damped and undamped oscillators. In particular, the damped oscillator is considered, with a forcing term whose frequency is close to the frequency of the free oscillations. For that problem, frequency-response curves are studied, both theoretically and through numerical computations, revealing a hysteresis phenomenon, when $Phi_{alpha,eta,p}$ is of constant sign.

  4. The Asymmetric Effects of Investor Sentiment

    DEFF Research Database (Denmark)

    Lutz, Chandler

    investors only act as corrective force during certain time periods. We also show that our index predicts implied volatility, media pessimism, and mutual fund flows. Overall, our findings are consistent with both the theories and anecdotal accounts of investor sentiment in the stock market.......We use the returns on lottery-like stocks to construct a novel index for investor sentiment in the stock market. This new measure is closely related to previously developed sentiment indicators, but more accurately tracks speculative episodes over the sample period. Using our index, we find...... that the relationship between sentiment and returns is asymmetric: during bear markets, high sentiment predicts low future returns for the cross-section of speculative stocks and the market overall while the relationship during bull markets is weak and often insignificant. Thus, the results suggest that sophisticated...

  5. Asymmetric pair distribution functions in catalysts

    DEFF Research Database (Denmark)

    Clausen, B. S.; Nørskov, Jens Kehlet

    2000-01-01

    it has been realized that often there is a need to use an improved EXAFS data analysis compared to the simple harmonic approach which works well for well-defined bulk structures. This is due to the fact that catalysts contain highly dispersed or disordered structures with pair distribution functions...... of asymmetric pair distribution functions for nano-sized particles and how they influence the structural parameters obtained from the standard data analysis. An alternative method, which takes into account deviations from the Gaussian pair distribution function typically used in the analysis of EXAFS spectra......, will be described. The method is based on an analysis of the pair distribution functions derived from molecular dynamics simulations of small metal particles and its reliability is demonstrated by comparing structural parameters obtained from independent X-ray diffraction experiments....

  6. Isospin dependent properties of asymmetric nuclear matter

    Science.gov (United States)

    Chowdhury, P. Roy; Basu, D. N.; Samanta, C.

    2009-07-01

    The density dependence of nuclear symmetry energy is determined from a systematic study of the isospin dependent bulk properties of asymmetric nuclear matter using the isoscalar and isovector components of the density dependent M3Y interaction. The incompressibility K∞ for the symmetric nuclear matter, the isospin dependent part Kasy of the isobaric incompressibility, and the slope L are all in excellent agreement with the constraints recently extracted from measured isotopic dependence of the giant monopole resonances in even-A Sn isotopes, from the neutron skin thickness of nuclei, and from analyses of experimental data on isospin diffusion and isotopic scaling in intermediate energy heavy-ion collisions. This work provides a fundamental basis for the understanding of nuclear matter under extreme conditions and validates the important empirical constraints obtained from recent experimental data.

  7. Do Daily Retail Gasoline Prices adjust Asymmetrically?

    International Nuclear Information System (INIS)

    Bettendorf, L.; Van der Geest, S.; Kuper, G.

    2005-04-01

    This paper analyzes adjustments in the Dutch retail gasoline prices. We estimate an error correction model on changes in the daily retail price for gasoline (taxes excluded) for the period 1996-2004 taking care of volatility clustering by estimating an EGARCH model. It turns out the volatility process is asymmetrical: an unexpected increase in the producer price has a larger effect on the variance of the producer price than an unexpected decrease. We do not find strong evidence for amount asymmetry. However, there is a faster reaction to upward changes in spot prices than to downward changes in spot prices. This implies timing or pattern asymmetry. This asymmetry starts three days after the change in the spot price and lasts for four days

  8. An asymmetric B Factory based on PEP

    International Nuclear Information System (INIS)

    Hutton, A.; Zisman, M.S.

    1990-06-01

    The study of rare and CP-violating B meson decays is well suited to a high-luminosity e + e - collider. For studying certain decay processes there are also substantial benefits associated with asymmetric beam energies, which give a moving center of mass for the B mesons. We describe a design for a 9 GeV x 3.1 GeV B Factory in the PEP tunnel that would operate initially at a luminosity of 3 x 10 33 cm -2 s -1 . Technical problems include issues related to high currents (e.g., beam instabilities, feedback systems, lifetime degradation and detector radiation power dissipation) and those related to the hetero-energetic beams (e.g., beam separation, beam-beam interaction and detector requirements). Issues requiring R ampersand D effort are identified. 8 refs., 2 figs., 2 tabs

  9. Mass asymmetric fission barriers for 75Br

    Science.gov (United States)

    Delis, D. N.; Blumenfeld, Y.; Bowman, D. R.; Colonna, N.; Hanold, K.; Jing, K.; Justice, M.; Meng, J. C.; Peaslee, G. F.; Wozniak, G. J.; Moretto, L. G.

    1991-11-01

    Fragments with atomic numbers covering nearly the entire range of the mass-asymmetry coordinate (4 < Z < 27) were observed from the 5.0, 6.2, 6.9, 8.0, 10.2 and 12.7 MeV/A 63Cu + 12C reactions. Energy spectra and angular distributions show the presence of projectile-like and target-like components along with an isotropic component. The isotropic component appears as a Coulomb ring in the invariant cross-section plots indicating the presence of a binary compound nucleus decay which is confirmed by the coincidence data. Excitation functions were constructed for each Z value and a nearly complete set of mass-asymmetric barriers has been extracted for 75Br. There is excellent agreement between the experimentally determined barriers and the finite-range model predictions.

  10. Baryon destruction by asymmetric dark matter

    International Nuclear Information System (INIS)

    Davoudiasl, Hooman; Morrissey, David E.; Tulin, Sean; Sigurdson, Kris

    2011-01-01

    We investigate new and unusual signals that arise in theories where dark matter is asymmetric and carries a net antibaryon number, as may occur when the dark matter abundance is linked to the baryon abundance. Antibaryonic dark matter can cause induced nucleon decay by annihilating visible baryons through inelastic scattering. These processes lead to an effective nucleon lifetime of 10 29 -10 32 yrs in terrestrial nucleon decay experiments, if baryon number transfer between visible and dark sectors arises through new physics at the weak scale. The possibility of induced nucleon decay motivates a novel approach for direct detection of cosmic dark matter in nucleon decay experiments. Monojet searches (and related signatures) at hadron colliders also provide a complementary probe of weak-scale dark-matter-induced baryon number violation. Finally, we discuss the effects of baryon-destroying dark matter on stellar systems and show that it can be consistent with existing observations.

  11. PEP-II: An asymmetric B factory

    International Nuclear Information System (INIS)

    1993-06-01

    In this report, the authors have described an updated conceptual design for the high-luminosity Asymmetric B Factory (PEP-II) to be built in the PEP tunnel culmination of more than four years of effort aimed at the design and construction of an asymmetric e + e - collider capable of achieving a luminosity of L = 3 x 10 33 cm -2 s -1 . All aspects of the conceptual design were scrutinized in March 1991 by a DOE technical review committee chaired by Dr. L. Edward Temple. The design was deemed feasible and capable of achieving its physics goals. Furthermore, the cost estimate, schedule, and management plan for the project were fully endorsed by the committee. This updated conceptual design report captures the technical progress since the March 1991 review and reflects the lower cost estimate corresponding to the improved design. Although the PEP-II design has continued to evolve, no technical scope changes have been made that invalidate the conclusion of the DOE review. The configuration adopted utilizes two storage rings, an electron ring operating at 9 GeV and a positron ring at 3.1 GeV, each with a circumference of 2200 m. The high-energy ring is an upgrade of the PEP storage ring at SLAC; all PEP magnets and most power supplies will be reused. The upgrade consists primarily of replacing the PEP vacuum chamber and RF system with newly designed versions optimized for the high-current environment of PEP-II. The low-energy ring will be newly constructed and will be situated atop the high-energy ring in the PEP tunnel. Utilities already installed in the PEP tunnel are largely sufficient to operate the two PEP-II storage rings

  12. Asymmetric collimation in breast cancer irradiation

    International Nuclear Information System (INIS)

    Isin, G.; Uzal, D.; Oezyar, E.; Arslan, G.; Akyol, F.; Atahan, I. L.

    1995-01-01

    Many methods have been devised to achieve an ideal match of the anterior supraclavicular field (SCV) caudal edge and the cephalad edges of the tangential fields. A non divergent SCV field edge is easily achieved using a half beam block. A number of methods are used to achieve a non divergent edge from the tangential beams including blocking, table angulation, collimator angulation in combination, and half beam blocking, collimator angulation. Using asymmetric collimation technique it is possible to achieve a perfect match-line at the junction of SCV and tangential fields. Via the longitudinal X-jaws, caudal edge of the SCV field and the cephalad margin of the tangential fields is defined. All three fields use one isocenter and thus a single set-up point by abutting beam-split fields at the match plane. The transverse Y jaws are used to beam-split the medial and lateral tangential fields at the chest wall level and define the lateral and medial edges of the SCV field. This technique eliminates lifting heavy half beam block, and the use of single isocenter is time-saving during set-up procedure. Computerized water phantom was utilized in dosimetric evaluations in this nonstandard technique. The match-line is clinically confirmed with verification film for each patient at first treatment. Our treatment planning system, Theraplan - Version 5B, is capable of asymmetric field planning. The 3-D treatment planning is performed at the central axis plane. Angle of tangential fields and source-skin distance at the set-up point is confirmed by 3D treatment planning

  13. Formation of defect-free 6FDA-DAM asymmetric hollow fiber membranes for gas separations

    KAUST Repository

    Xu, Liren

    2014-06-01

    This paper reports the formation of defect-free 6FDA-DAM asymmetric hollow fiber membranes. 6FDA-polyimides are of great interest for advanced gas separation membranes, and 6FDA-DAM polyimide is a representative polymer in this family with attractive dense film properties for several potential applications. The work reported here for the 6FDA-DAM polyimide provides insight for the challenging fabrication of defect-free asymmetric hollow fiber membranes for this class of 6FDA-polyimides, which behave rather different from lower free volume polymers. Specifically, the 6FDA based materials show relatively slow phase separation rate in water quench baths, which presents a challenge for fiber spinning. For convenience, we refer to the behavior as more "non-solvent resistant" in comparison to other lower free volume polymers, since the binodal phase boundary is displaced further from the conventional position near the pure polymer-solvent axis on a ternary phase diagram in conventional polymers like Matrimid® and Ultem®. The addition of lithium nitrate to promote phase separation has a useful impact on 6FDA-DAM asymmetric hollow fiber formation. 6FDA-DAM phase diagrams using ethanol and water as non-solvent are reported, and it was found that water is less desirable as a non-solvent dope additive for defect-free fiber spinning. Phase diagrams are also reported for 6FDA-DAM dope formulation with and without the addition of lithium nitrate, and defect-free asymmetric hollow fiber membranes are reported for both cases. The effect of polymer molecular weight on defect-free fiber spinning was also investigated. Gas transport properties and morphology of hollow fibers were characterized. With several thorough case studies, this work provides a systematic guideline for defect-free fiber formation from 6FDA-polymers. © 2014 Elsevier B.V.

  14. Likelihood for transcriptions in a genetic regulatory system under asymmetric stable Lévy noise

    Science.gov (United States)

    Wang, Hui; Cheng, Xiujun; Duan, Jinqiao; Kurths, Jürgen; Li, Xiaofan

    2018-01-01

    This work is devoted to investigating the evolution of concentration in a genetic regulation system, when the synthesis reaction rate is under additive and multiplicative asymmetric stable Lévy fluctuations. By focusing on the impact of skewness (i.e., non-symmetry) in the probability distributions of noise, we find that via examining the mean first exit time (MFET) and the first escape probability (FEP), the asymmetric fluctuations, interacting with nonlinearity in the system, lead to peculiar likelihood for transcription. This includes, in the additive noise case, realizing higher likelihood of transcription for larger positive skewness (i.e., asymmetry) index β, causing a stochastic bifurcation at the non-Gaussianity index value α = 1 (i.e., it is a separating point or line for the likelihood for transcription), and achieving a turning point at the threshold value β≈-0.5 (i.e., beyond which the likelihood for transcription suddenly reversed for α values). The stochastic bifurcation and turning point phenomena do not occur in the symmetric noise case (β = 0). While in the multiplicative noise case, non-Gaussianity index value α = 1 is a separating point or line for both the MFET and the FEP. We also investigate the noise enhanced stability phenomenon. Additionally, we are able to specify the regions in the whole parameter space for the asymmetric noise, in which we attain desired likelihood for transcription. We have conducted a series of numerical experiments in "regulating" the likelihood of gene transcription by tuning asymmetric stable Lévy noise indexes. This work offers insights for possible ways of achieving gene regulation in experimental research.

  15. Atomically Precise Metal Nanoclusters for Catalytic Application

    Energy Technology Data Exchange (ETDEWEB)

    Jin, Rongchao [Carnegie Mellon Univ., Pittsburgh, PA (United States)

    2016-11-18

    The central goal of this project is to explore the catalytic application of atomically precise gold nanoclusters. By solving the total structures of ligand-protected nanoclusters, we aim to correlate the catalytic properties of metal nanoclusters with their atomic/electronic structures. Such correlation unravel some fundamental aspects of nanocatalysis, such as the nature of particle size effect, origin of catalytic selectivity, particle-support interactions, the identification of catalytically active centers, etc. The well-defined nanocluster catalysts mediate the knowledge gap between single crystal model catalysts and real-world conventional nanocatalysts. These nanoclusters also hold great promise in catalyzing certain types of reactions with extraordinarily high selectivity. These aims are in line with the overall goals of the catalytic science and technology of DOE and advance the BES mission “to support fundamental research to understand, predict, and ultimately control matter and energy at the level of electrons, atoms, and molecules”. Our group has successfully prepared different sized, robust gold nanoclusters protected by thiolates, such as Au25(SR)18, Au28(SR)20, Au38(SR)24, Au99(SR)42, Au144(SR)60, etc. Some of these nanoclusters have been crystallographically characterized through X-ray crystallography. These ultrasmall nanoclusters (< 2 nm diameter) exhibit discrete electronic structures due to quantum size effect, as opposed to quasicontinuous band structure of conventional metal nanoparticles or bulk metals. The available atomic structures (metal core plus surface ligands) of nanoclusters serve as the basis for structure-property correlations. We have investigated the unique catalytic properties of nanoclusters (i.e. not observed in conventional nanogold catalysts) and revealed the structure-selectivity relationships. Highlights of our

  16. Catalytic Combustor for Fuel-Flexible Turbine

    Energy Technology Data Exchange (ETDEWEB)

    W. R. Laster; E. Anoshkina

    2008-01-31

    Under the sponsorship of the U. S. Department of Energy's National Energy Technology Laboratory, Siemens Westinghouse has conducted a three-year program to develop an ultra low NOx, fuel flexible catalytic combustor for gas turbine application in IGCC. The program is defined in three phases: Phase 1 - Implementation Plan, Phase 2 - Validation Testing and Phase 3 - Field Testing. Both Phase 1 and Phase 2 of the program have been completed. In IGCC power plants, the gas turbine must be capable of operating on syngas as a primary fuel and an available back-up fuel such as natural gas. In this program the Rich Catalytic Lean (RCLTM) technology is being developed as an ultra low NOx combustor. In this concept, ultra low NOx is achieved by stabilizing a lean premix combustion process by using a catalytic reactor to oxidize a portion of the fuel, increasing the temperature of fuel/air mixture prior to the main combustion zone. In Phase 1, the feasibility of the catalytic concept for syngas application has been evaluated and the key technology issues identified. In Phase II the technology necessary for the application of the catalytic concept to IGCC fuels was developed through detailed design and subscale testing. Phase III (currently not funded) will consist of full-scale combustor basket testing on natural gas and syngas.

  17. Catalytic Combustor for Fuel-Flexible Turbine

    Energy Technology Data Exchange (ETDEWEB)

    Laster, W. R.; Anoshkina, E.

    2008-01-31

    Under the sponsorship of the U. S. Department of Energy’s National Energy Technology Laboratory, Siemens Westinghouse has conducted a three-year program to develop an ultra low NOx, fuel flexible catalytic combustor for gas turbine application in IGCC. The program is defined in three phases: Phase 1- Implementation Plan, Phase 2- Validation Testing and Phase 3 – Field Testing. Both Phase 1 and Phase 2 of the program have been completed. In IGCC power plants, the gas turbine must be capable of operating on syngas as a primary fuel and an available back-up fuel such as natural gas. In this program the Rich Catalytic Lean (RCLTM) technology is being developed as an ultra low NOx combustor. In this concept, ultra low NOx is achieved by stabilizing a lean premix combustion process by using a catalytic reactor to oxidize a portion of the fuel, increasing the temperature of fuel/air mixture prior to the main combustion zone. In Phase 1, the feasibility of the catalytic concept for syngas application has been evaluated and the key technology issues identified. In Phase II the technology necessary for the application of the catalytic concept to IGCC fuels was developed through detailed design and subscale testing. Phase III (currently not funded) will consist of full-scale combustor basket testing on natural gas and syngas.

  18. Catalytic Reduction of NO and NOx Content in Tobacco Smoke

    Directory of Open Access Journals (Sweden)

    Cvetkovic N

    2014-12-01

    Full Text Available In order to reduce the nitric oxide (NO and nitrogen oxides (NO content in mainstream tobacco smoke, a new class of catalyst based on Cu-ZSM-5 zeolite has been synthesized. The effectiveness of the new catalyst (degree of reduction and specific catalytic ability was tested both by adding Cu-ZSM-5 zeolite directly to the tobacco blend and by addition to the filter. We have determined that adding the catalyst to the tobacco blend does not cause any changes in the physical, chemical or organoleptic properties of the cigarette blend. But, the addition reduces the yield of nitrogen oxides while having no influence on nicotine and “tar” content in the tobacco smoke of the modified blend. The catalyst addition increases the static burning rate (SBR. The changes in the quantity of NO and NOmay be explained by changes in burning conditions due to the increase of Oobtained from catalytic degradation of NO and NO, and adsorptive and diffusive properties of the catalyst. The changes in mainstream smoke analytes are also given on a puff-by-puff basis.

  19. Asymmetric Transfer Hydrogenation of Ketones with Modified Grubbs Metathesis Catalysts : On the Way to a Tandem Process

    NARCIS (Netherlands)

    Renom-Carrasco, Marc; Gajewski, Piotr; Pignataro, Luca; de Vries, Johannes G.; Piarulli, Umberto; Gennari, Cesare; Lefort, Laurent

    2016-01-01

    Herein, we report the successful transformation of a 1(st) generation Grubbs metathesis catalyst into an asymmetric transfer hydrogenation (ATH) catalyst. Upon addition of a chiral amine ligand, an alcohol and a base, the 1(st) generation Hoveyda-Grubbs catalyst (HG-I) was found to promote the

  20. Asymmetric Synthesis of (-)-Incarvillateine Employing an Intramolecular Alkylation via Rh-Catalyzed Olefinic C-H Bond Activation

    Energy Technology Data Exchange (ETDEWEB)

    Tsai, Andy; Bergman, Robert; Ellman, Jonathan

    2008-02-18

    An asymmetric total synthesis of (-)-incarvillateine, a natural product having potent analgesic properties, has been achieved in 11 steps and 15.4% overall yield. The key step is a rhodium-catalyzed intramolecular alkylation of an olefinic C-H bond to set two stereocenters. Additionally, this transformation produces an exocyclic, tetrasubstituted alkene through which the bicyclic piperidine moiety can readily be accessed.

  1. 40 CFR Table 42 to Subpart Uuu of... - Additional Information for Initial Notification of Compliance Status

    Science.gov (United States)

    2010-07-01

    ... Refineries: Catalytic Cracking Units, Catalytic Reforming Units, and Sulfur Recovery Units Pt. 63, Subpt. UUU... applies to you. For . . . You shall provide this additional information . . . 1. Identification of... compliance Identification of each emission limitation you will meet for each affected source, including any...

  2. Complexation-tailored morphology of asymmetric block copolymer membranes

    KAUST Repository

    Madhavan, Poornima

    2013-08-14

    Hydrogen-bond formation between polystyrene-b-poly (4-vinylpyridine) (PS-b-P4VP) block copolymer (BCP) and -OH/-COOH functionalized organic molecules was used to tune morphology of asymmetric nanoporous membranes prepared by simultaneous self-assembly and nonsolvent induced phase separation. The morphologies were characterized by field emmision scanning electron microscopy (FESEM) and atomic force microscopy (AFM). Hydrogen bonds were confirmed by infrared (IR), and the results were correlated to rheology characterization. The OH-functionalized organic molecules direct the morphology into hexagonal order. COOH-functionalized molecules led to both lamellar and hexagonal structures. Micelle formation in solutions and their sizes were determined using dynamic light scattering (DLS) measurements and water fluxes of 600-3200 L/m 2·h·bar were obtained. The pore size of the plain BCP membrane was smaller than with additives. The following series of additives led to pores with hexagonal order with increasing pore size: terephthalic acid (COOH-bifunctionalized) < rutin (OH-multifunctionalized) < 9-anthracenemethanol (OH-monofunctionalized) < 3,5-dihydroxybenzyl alcohol (OH-trifunctionalized). © 2013 American Chemical Society.

  3. FE Simulation of the Stress-Strain State during Shear-Compression Testing and Asymmetric Three-Roll Rolling Process

    Directory of Open Access Journals (Sweden)

    Pesin Alexander

    2017-01-01

    Full Text Available A three-roll rolling process is a significant technique in the production of wire rod, round bars and hexagonal profiles for structural applications. Better mechanical properties of wire rod, round bars and hexagonal profiles can be achieved due to large plastic deformation by the three-roll rolling process. Asymmetric rolling is a novel technique characterized by a kinematic asymmetry linked to the difference in peripheral speed of the rolls, able to introduce additional shear strains through the bar thickness. Physical simulation of shear strain, which is similar to that occurring in asymmetric three-roll rolling process, is very important for design of technology of producing ultrafine grain materials. Shear testing is complicated by the fact that a state of large shear is not easily achievable in most specimen geometries. Application of the shear-compression testing and specimen geometry to physical simulation of asymmetric three-roll rolling process is discussed in the paper. FEM simulation and comparison of the stress-strain state during shear-compression testing and asymmetric three-roll rolling process is presented. The results of investigation can be used to optimize the physical simulation of asymmetric three-roll rolling processes and for design of technology of producing ultrafine grain materials by severe plastic deformation.

  4. SambVca 2. A Web Tool for Analyzing Catalytic Pockets with Topographic Steric Maps

    KAUST Repository

    Falivene, Laura

    2016-06-27

    Developing more efficient catalysts remains one of the primary targets of organometallic chemists. To accelerate reaching this goal, effective molecular descriptors and visualization tools can represent a remarkable aid. Here, we present a Web application for analyzing the catalytic pocket of metal complexes using topographic steric maps as a general and unbiased descriptor that is suitable for every class of catalysts. To show the broad applicability of our approach, we first compared the steric map of a series of transition metal complexes presenting popular mono-, di-, and tetracoordinated ligands and three classic zirconocenes. This comparative analysis highlighted similarities and differences between totally unrelated ligands. Then, we focused on a recently developed Fe(II) catalyst that is active in the asymmetric transfer hydrogenation of ketones and imines. Finally, we expand the scope of these tools to rationalize the inversion of enantioselectivity in enzymatic catalysis, achieved by point mutation of three amino acids of mononuclear p-hydroxymandelate synthase.

  5. Symmetry in Cascade Chirality-Transfer Processes: A Catalytic Atroposelective Direct Arylation Approach to BINOL Derivatives.

    Science.gov (United States)

    Wang, Jin-Zheng; Zhou, Jin; Xu, Chang; Sun, Hongbin; Kürti, László; Xu, Qing-Long

    2016-04-27

    Herein we disclose a scalable organocatalytic direct arylation approach for the regio- and atroposelective synthesis of non-C2-symmetric 2,2'-dihydroxy-1,1'-binaphthalenes (BINOLs). In the presence of catalytic amounts of axially chiral phosphoric acids, phenols and naphthols are coupled with iminoquinones via a cascade process that involves sequential aminal formation, sigmatropic rearrangement, and rearomatization to afford enantiomerically enriched BINOL derivatives in good to excellent yields. Our studies suggest that the (local) symmetry of the initially formed aminal intermediate has a dramatic impact on the level of enantioinduction in the final product. Aminals with a plane of symmetry give rise to BINOL derivatives with significantly lower enantiomeric excess than unsymmetrical ones featuring a stereogenic center. Presumably asymmetric induction in the sigmatropic rearrangement step is significantly more challenging than during aminal formation. Sigmatropic rearrangement of the enantiomerically enriched aminal and subsequent rearomatization transfers the central chirality into axial chirality with high fidelity.

  6. Core-shell and asymmetric polystyrene-gold composite particles via one-step Pickering emulsion polymerization.

    Science.gov (United States)

    Zhang, Mingmeng; Ngo, Thao H; Rabiah, Noelle I; Otanicar, Todd P; Phelan, Patrick E; Swaminathan, Raja; Dai, Lenore L

    2014-01-14

    Core-shell structured polystyrene-gold composite particles are synthesized from one-step Pickering emulsion polymerization. The surface coverage of the core-shell composite particles is improved with increasing gold nanoparticle (AuNP) hydrophobicity and concentration. At high surface coverage, the AuNPs exhibit an ordered hexagonal pattern, likely due to electrostatic repulsion during the emulsion polymerization process. In addition to core-shell structured polystyrene-gold composite particles, an intriguing observation is that at low AuNP concentrations, asymmetric polystyrene-gold nanocomposite particles are simultaneously formed, where a single gold nanoparticle is attached onto each polystyrene particle. It is found that these asymmetric particles are formed via a "seeded-growth" mechanism. The core-shell and asymmetric polystyrene-gold composite particles prove to be efficient catalysts as they successfully catalyze the Rhodamine B reduction reaction with stable performance and show high recyclability as catalysts.

  7. Highly Dense Isolated Metal Atom Catalytic Sites

    DEFF Research Database (Denmark)

    Chen, Yaxin; Kasama, Takeshi; Huang, Zhiwei

    2015-01-01

    -ray diffraction. A combination of electron microscopy images with X-ray absorption spectra demonstrated that the silver atoms were anchored on five-fold oxygen-terminated cavities on the surface of the support to form highly dense isolated metal active sites, leading to excellent reactivity in catalytic oxidation......Atomically dispersed noble-metal catalysts with highly dense active sites are promising materials with which to maximise metal efficiency and to enhance catalytic performance; however, their fabrication remains challenging because metal atoms are prone to sintering, especially at a high metal...... loading. A dynamic process of formation of isolated metal atom catalytic sites on the surface of the support, which was achieved starting from silver nanoparticles by using a thermal surface-mediated diffusion method, was observed directly by using in situ electron microscopy and in situ synchrotron X...

  8. Throughput Analysis of Full Duplex Communication with Asymmetric Traffic in Small Cell Systems

    DEFF Research Database (Denmark)

    Mahmood, Nurul Huda; Berardinelli, Gilberto; Mogensen, Preben Elgaard

    2015-01-01

    Full duplex communication promises a 100% throughput gain by enabling simultaneous transmission and reception. However, such simultaneous communication leads to a corresponding increase in the network interference. In addition, full duplex communication can only be exploited when traffic...... is available in both uplink and downlink directions; while, cellular network traffic tend to be downlink heavy in practice. The potential throughput gains of full duplex communication over conventional half duplex transmission in a small cell network with asymmetric traffic conditions are investigated...... in this contribution using network analysis tools from stochastic geometry. The analytical findings are further confirmed through computer-based Monte-Carlo simulations. Asymmetric downlink/uplink traffic pattern and the increased network interference stemming from full duplex transmissions are found to limit its...

  9. Spontaneous Giving under Structural Inequality: Intuition Promotes Cooperation in Asymmetric Social Dilemmas.

    Directory of Open Access Journals (Sweden)

    Sebastian Lotz

    Full Text Available The present research investigates the role of intuitive mental processing on cooperation in experimental games involving structural inequality. Results from an experiment using conceptual priming to induce intuitive mental processing provide the first evidence that cooperation is promoted by intuition in an asymmetric context that distributes the gains from cooperation unequally among a group. Therefore, the results extend our understanding of the cognitive underpinnings of human cooperation by demonstrating the robustness of intuitive cooperation in games involving structural inequality regarding asymmetric gains from cooperation. Additionally, the results provide the first successful conceptual replication of the intuition-cooperation link using conceptual priming, therefore also contributing to the debate about the validity of previous research in other contexts. Taken together, the present research contributes to the literature on psychological and institutional mechanisms that promote cooperation.

  10. Dislocation Nucleation on Grain Boundaries: Low Angle Twist and Asymmetric Tilt Boundaries

    Directory of Open Access Journals (Sweden)

    Erman Guleryuz

    2016-07-01

    Full Text Available We investigate the mechanisms of incipient plasticity at low angle twist and asymmetric tilt boundaries in fcc metals. To observe plasticity of grain boundaries independently of the bulk plasticity, we simulate nanoindentation of bicrystals. On the low angle twist boundaries, the intrinsic grain boundary (GB dislocation network deforms under load until a dislocation segment compatible with glide on a lattice slip plane is created. The half loops are then emitted into the bulk of the crystal. Asymmetric twist boundaries considered here did not produce bulk dislocations under load. Instead, the boundary with a low excess volume nucleated a mobile GB dislocation and additional GB defects. The GB sliding proceeded by motion of the mobile GB dislocation. The boundary with a high excess volume sheared elastically, while bulk-nucleated dislocations produced plastic relaxation.

  11. Asymmetric double quantum well structure as a tunable detector in the far-infrared range

    CERN Document Server

    Shin, U; Park, M J; Lee, S J

    1999-01-01

    The eigenvalues and the wave functions of GaAs/Al sub x Ga sub 1 sub - sub x As asymmetric double quantum well structure have been calculated by using of complex energy method. Based on theoretical calculations, tuning ranges from 9 to 14 mu m are predicted for the proposed asymmetric coupled-quantum-well structure. In addition we calculated the energy eigenvalues and the wave functions of an electron in GaAs/Al sub x Ga sub 1 sub - sub x As single quantum well structure (including delta-perturbation). the variation in E sub 1 , the ground state energy eigenvalue of the electron, depends on the strength and position of the perturbation within the well.

  12. Characterization of catalytic supports based in mixed oxides for control reactions of NO and N2O

    International Nuclear Information System (INIS)

    Garcia C, M.A.; Perez H, R.; Gomez C, A.; Diaz, G.

    1999-01-01

    The catalytic supports Al 2 O 3 , La 2 O 3 and Al 2 O 3 -La 2 O 3 were prepared by the Precipitation and Coprecipitation techniques. The catalytic supports Al 2 O 3 , La 2 O 3 and Al 2 O 3 -La 2 O 3 were characterized by several techniques to determine: texture (Bet), crystallinity (XRD), chemical composition (Sem)(Ftir) and it was evaluated their total acidity by reaction with 2-propanol. The investigation will be continued with the cobalt addition and this will be evaluated for its catalytic activity in control reactions of N O and N 2 O. (Author)

  13. Porous media for catalytic renewable energy conversion

    Science.gov (United States)

    Hotz, Nico

    2012-05-01

    A novel flow-based method is presented to place catalytic nanoparticles into a reactor by sol-gelation of a porous ceramic consisting of copper-based nanoparticles, silica sand, ceramic binder, and a gelation agent. This method allows for the placement of a liquid precursor containing the catalyst into the final reactor geometry without the need of impregnating or coating of a substrate with the catalytic material. The so generated foam-like porous ceramic shows properties highly appropriate for use as catalytic reactor material, e.g., reasonable pressure drop due to its porosity, high thermal and catalytic stability, and excellent catalytic behavior. The catalytic activity of micro-reactors containing this foam-like ceramic is tested in terms of their ability to convert alcoholic biofuel (e.g. methanol) to a hydrogen-rich gas mixture with low concentrations of carbon monoxide (up to 75% hydrogen content and less than 0.2% CO, for the case of methanol). This gas mixture is subsequently used in a low-temperature fuel cell, converting the hydrogen directly to electricity. A low concentration of CO is crucial to avoid poisoning of the fuel cell catalyst. Since conventional Polymer Electrolyte Membrane (PEM) fuel cells require CO concentrations far below 100 ppm and since most methods to reduce the mole fraction of CO (such as Preferential Oxidation or PROX) have CO conversions of up to 99%, the alcohol fuel reformer has to achieve initial CO mole fractions significantly below 1%. The catalyst and the porous ceramic reactor of the present study can successfully fulfill this requirement.

  14. Asymmetric fluorination of α-branched cyclohexanones enabled by a combination of chiral anion phase-transfer catalysis and enamine catalysis using protected amino acids.

    Science.gov (United States)

    Yang, Xiaoyu; Phipps, Robert J; Toste, F Dean

    2014-04-09

    We report a study involving the successful merger of two separate chiral catalytic cycles: a chiral anion phase-transfer catalysis cycle to activate Selectfluor and an enamine activation cycle, using a protected amino acid as organocatalyst. We have demonstrated the viability of this approach with the direct asymmetric fluorination of α-substituted cyclohexanones to generate quaternary fluorine-containing stereocenters. With these two chiral catalytic cycles operating together in a matched sense, high enantioselectivites can be achieved, and we envisage that this dual catalysis method has the potential to be more broadly applicable, given the breadth of enamine catalysis. It also represents a rare example of chiral enamine catalysis operating successfully on α-branched ketones, substrates commonly inert to this activation mode.

  15. Toward a catalytic site in DNA

    DEFF Research Database (Denmark)

    Jakobsen, Ulla; Rohr, Katja; Vogel, Stefan

    2007-01-01

    A number of functionalized polyaza crown ether building blocks have been incorporated into DNA-conjugates as catalytic Cu(2+) binding sites. The effect of the DNA-conjugate catalyst on the stereochemical outcome of a Cu(2+)-catalyzed Diels-Alder reaction will be presented.......A number of functionalized polyaza crown ether building blocks have been incorporated into DNA-conjugates as catalytic Cu(2+) binding sites. The effect of the DNA-conjugate catalyst on the stereochemical outcome of a Cu(2+)-catalyzed Diels-Alder reaction will be presented....

  16. Thermal and catalytic pyrolysis of plastic waste

    Directory of Open Access Journals (Sweden)

    Débora Almeida

    2016-02-01

    Full Text Available Abstract The amount of plastic waste is growing every year and with that comes an environmental concern regarding this problem. Pyrolysis as a tertiary recycling process is presented as a solution. Pyrolysis can be thermal or catalytical and can be performed under different experimental conditions. These conditions affect the type and amount of product obtained. With the pyrolysis process, products can be obtained with high added value, such as fuel oils and feedstock for new products. Zeolites can be used as catalysts in catalytic pyrolysis and influence the final products obtained.

  17. Catalytic Wastewater Treatment Using Pillared Clays

    Science.gov (United States)

    Perathoner, Siglinda; Centi, Gabriele

    After introduction on the use of solid catalysts in wastewater treatment technologies, particularly advanced oxidation processes (AOPs), this review discussed the use of pillared clay (PILC) materials in three applications: (i) wet air catalytic oxidation (WACO), (ii) wet hydrogen peroxide catalytic oxidation (WHPCO) on Cu-PILC and Fe-PILC, and (iii) behavior of Ti-PILC and Fe-PILC in the photocatalytic or photo-Fenton conversion of pollutants. Literature data are critically analyzed to evidence the main direction to further investigate, in particularly with reference to the possible practical application of these technologies to treat industrial, municipal, or agro-food production wastewater.

  18. Catalytic gasification of oil-shales

    Energy Technology Data Exchange (ETDEWEB)

    Lapidus, A.; Avakyan, T. [I.M. Gubkin Russian State Univ. of Oil and Gas, Moscow (Russian Federation); Strizhakova, Yu. [Samara State Univ. (Russian Federation)

    2012-07-01

    Nowadays, the problem of complex usage of solid fossil fuels as raw materials for obtaining of motor fuels and chemical products is becoming increasingly important. A one of possible solutions of the problem is their gasification with further processing of gaseous and liquid products. In this work we have investigated the process of thermal and catalytic gasification of Baltic and Kashpir oil-shales. We have shown that, as compared with non-catalytic process, using of nickel catalyst in the reaction increases the yield of gas, as well as hydrogen content in it, and decreases the amount of liquid products. (orig.)

  19. Development of a solid-phase 'asymmetric resin-capture-release' process: application of an ephedrine chiral resin in an approach to gamma-butyrolactones.

    Science.gov (United States)

    Kerrigan, Nessan J; Hutchison, Panee C; Heightman, Tom D; Procter, David J

    2004-09-07

    The potential of a solid-phase asymmetric resin-capture-release strategy for high-throughput synthesis has been evaluated. Fukuzawa's Sm(ii)-mediated, asymmetric approach to gamma-butyrolactones was selected to illustrate the feasibility of such a process. Alpha,beta-unsaturated esters immobilised on an ephedrine chiral resin have been applied in an asymmetric approach to gamma-butyrolactones. Lactone products are obtained in moderate isolated yields with selectivities up to 96% ee. In addition, we have shown that the ephedrine resin can be conveniently recovered and recycled although in some cases lower yields were obtained on reuse of the chiral resin. A short synthesis of a moderate DNA-binding microbial metabolite using asymmetric resin-capture-release is also described. Copyright 2004 The Royal Society of Chemistry

  20. SOLAR CONSTRAINTS ON ASYMMETRIC DARK MATTER

    International Nuclear Information System (INIS)

    Lopes, Ilídio; Silk, Joseph

    2012-01-01

    The dark matter content of the universe is likely to be a mixture of matter and antimatter, perhaps comparable to the measured asymmetric mixture of baryons and antibaryons. During the early stages of the universe, the dark matter particles are produced in a process similar to baryogenesis, and dark matter freezeout depends on the dark matter asymmetry and the annihilation cross section (s-wave and p-wave annihilation channels) of particles and antiparticles. In these η-parameterized asymmetric dark matter (ηADM) models, the dark matter particles have an annihilation cross section close to the weak interaction cross section, and a value of dark matter asymmetry η close to the baryon asymmetry η B . Furthermore, we assume that dark matter scattering of baryons, namely, the spin-independent scattering cross section, is of the same order as the range of values suggested by several theoretical particle physics models used to explain the current unexplained events reported in the DAMA/LIBRA, CoGeNT, and CRESST experiments. Here, we constrain ηADM by investigating the impact of such a type of dark matter on the evolution of the Sun, namely, the flux of solar neutrinos and helioseismology. We find that dark matter particles with a mass smaller than 15 GeV, a spin-independent scattering cross section on baryons of the order of a picobarn, and an η-asymmetry with a value in the interval 10 –12 -10 –10 , would induce a change in solar neutrino fluxes in disagreement with current neutrino flux measurements. This result is also confirmed by helioseismology data. A natural consequence of this model is suppressed annihilation, thereby reducing the tension between indirect and direct dark matter detection experiments, but the model also allows a greatly enhanced annihilation cross section. All the cosmological ηADM scenarios that we discuss have a relic dark matter density Ωh 2 and baryon asymmetry η B in agreement with the current WMAP measured values, Ω DM h 2 = 0

  1. Asymmetric Branching in Biological Resource Distribution Networks

    Science.gov (United States)

    Brummer, Alexander Byers

    There is a remarkable relationship between an organism's metabolic rate (resting power consumption) and the organism's mass. It may be a universal law of nature that an organism's resting metabolic rate is proportional to its mass to the power of 3/4. This relationship, known as Kleiber's Law, appears to be valid for both plants and animals. This law is important because it implies that larger organisms are more efficient than smaller organisms, and knowledge regarding metabolic rates are essential to a multitude of other fields in ecology and biology. This includes modeling the interactions of many species across multiple trophic levels, distributions of species abundances across large spatial landscapes, and even medical diagnostics for respiratory and cardiovascular pathologies. Previous models of vascular networks that seek to identify the origin of metabolic scaling have all been based on the unrealistic assumption of perfectly symmetric branching. In this dissertation I will present a theory of asymmetric branching in self-similar vascular networks (published by Brummer et al. in [9]). The theory shows that there can exist a suite of vascular forms that result in the often observed 3/4 metabolic scaling exponent of Kleiber's Law. Furthermore, the theory makes predictions regarding major morphological features related to vascular branching patterns and their relationships to metabolic scaling. These predictions are suggestive of evolutionary convergence in vascular branching. To test these predictions, I will present an analysis of real mammalian and plant vascular data that shows: (i) broad patterns in vascular networks across entire animal kingdoms and (ii) within these patterns, plant and mammalian vascular networks can be uniquely distinguished from one another (publication in preparation by Brummer et al.). I will also present results from a computational study in support of point (i). Namely, that asymmetric branching may be the optimal strategy to

  2. High temperature solid state catalytic isotope exchange with deuterium and tritium

    International Nuclear Information System (INIS)

    Zolotarev, Yu.A.; Kozik, V.S.; Dorokhova, E.M.; Zaitsev, D.A., Myasoedov, N.F.; Rozenberg, S.G.

    1992-01-01

    A method for synthesizing tritium- or deuterium-labeled amino acids, peptides and biogenic amines through high temperature solid state catalytic isotope exchange (HSCIE) is proposed. The dependence of the degree of isotope exchange in HSCIE on the structure of the compound, the reactivity of hydrogen at different carbon atoms and the conditions of the process has been examined. If HSCIE is performed in the temperature range of 373 to 413 K, the selectivity of isotopic label incorporation comes to 70% or higher. When the tritium label is introduced into peptides, they retain the configuration of asymmetric atoms, even upon the substitution of tritium for hydrogen at the α-carbon atoms of the amino acid residues. HSCIE at 453-513 K leads to an even distribution of the isotopic label over the organic compound molecule. The results of 3 H NMR spectroscopy highlighting the distribution of the tritium label in the organic compound molecules are presented. The configuration of asymmetric atoms in amino acids is preserved to a high extent upon 80-90% substitution of isotopes for hydrogen atoms. (author) 13 refs.; 4 figs.;

  3. Direct Catalytic Asymmetric Mannich Reaction with Dithiomalonates as Excellent Mannich Donors: Organocatalytic Synthesis of (R)-Sitagliptin.

    Science.gov (United States)

    Bae, Han Yong; Kim, Mun Jong; Sim, Jae Hun; Song, Choong Eui

    2016-08-26

    In this study, dithiomalonates (DTMs) were demonstrated to be exceptionally efficient Mannich donors in terms of reactivity and stereoselectivity in cinchona-based-squaramide-catalyzed enantioselective Mannich reactions of diverse imines or α-amidosulfones as imine surrogates. Owing to the superior reactivity of DTMs as compared to conventional malonates, the catalyst loading could be reduced to 0.1 mol % without the erosion of enantioselectivity (up to 99 % ee). Furthermore, by the use of a DTM, even some highly challenging primary alkyl α-amidosulfones were smoothly converted into the desired adducts with excellent enantioselectivity (up to 97 % ee), whereas the use of a malonate or monothiomalonate resulted in no reaction under identical conditions. The synthetic utility of the chiral Mannich adducts obtained from primary alkyl substrates was highlighted by the organocatalytic, coupling-reagent-free synthesis of the antidiabetic drug (-)-(R)-sitagliptin. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Enantioselective conjugate addition nitro-Mannich reactions: solvent controlled synthesis of acyclic anti- and syn-β-nitroamines with three contiguous stereocenters.

    Science.gov (United States)

    Anderson, James C; Stepney, Gregory J; Mills, Matthew R; Horsfall, Lisa R; Blake, Alexander J; Lewis, William

    2011-04-01

    We report an enantioselective conjugate addition nitro-Mannich reaction protocol which combines dialkylzinc, aromatic nitro alkene and imine to form two C-C bonds and three contiguous stereocenters in one reaction vessel. Absolute stereochemistry was controlled from the initial 1,4-addition of dialkylzinc to aromatic nitroalkenes by known copper-chiral ligand catalysts. The choice of solvent dictated the formation of either the syn,anti or syn,syn diastereoisomers, two of the four possible diastereoisomers. The syn,syn isomer is a rare example of a syn-selective nitro-Mannich reaction. The diastereoselectivity is dependent upon the presence or not of Zn(O(2)CCF(3))(2) in the reaction mixture and empirical transition state models are proposed to account for the observed stereochemical course of the two reaction conditions. The extent of enantioselectivity and structural diversity of the process is limited by current methodology for the catalytic asymmetric addition of dialkylzincs to nitrostyrenes. The synthetically versatile products are the most complex β-nitro amines prepared using the nitro-Mannich reaction and are formed in high yield and enantioselectivity.

  5. Heterogeneous Catalytic Oligomerization of Ethylene

    Science.gov (United States)

    Jan, Oliver Dennis

    increased with temperature, with 17 wt.% observed at 190ºC. Higher reaction temperatures led to the formation of odd-numbered oligomers primarily due to acid-catalyzed cracking reactions. In the range of space velocities tested, a moderate WHSV of 2.0 hr-1 resulted in a local maximum of 10.6 wt.% of liquid hydrocarbon yield. A moderate nickel loading of 3.4 wt.% also resulted in the highest liquid yield out of the three loadings tested (10.6 wt.%). The variation in nickel loading revealed the importance of having a synergistic balance of nickel and acid sites on the catalyst to maximize ethylene conversion and maintain high liquid hydrocarbon yield. Lastly, we used supercritical ethylene as both a solvent and as a reactant for ethylene oligomerization over two silica-alumina type catalysts: Ni-Hbeta and Ni-Al-SBA-15. Specifically, the effect of pressure and temperature on the overall conversion and product selectivity were evaluated in the range from 0 to 65 bar and 30 to 120ºC. At subcritical conditions, the ethylene conversion reached a plateau of around 50%. By increasing the pressure past the critical point of ethylene, the conversion drastically increased to 71%. The increased conversion can be attributed to the solubility of certain oligomers, namely butene, in supercritical ethylene that promotes desorption from catalytic active site before further oligomerization. We also tested a mesoporous catalyst, Ni-Al-SBA-15 and observed conversion trends analogous to that of Ni-Hbeta. At supercritical conditions, ethylene oligomerization over Ni-Al-SBA-15 was more selective towards the butene product, with nearly 74 wt.% butenes observed. The catalyst activity increased with temperature from 30ºC to 120ºC. The experiment conducted at 30ºC showed very little activity and ethylene conversion, however it effectively heavy molecular weight species from the catalyst. This condition, albeit being not effective for ethylene oligomerization, could be implemented as an in

  6. Solid-state molecular organometallic chemistry. Single-crystal to single-crystal reactivity and catalysis with light hydrocarbon substrates† †Electronic supplementary information (ESI) available: Full details of experimental details, spectroscopic and other analytical data, X-ray crystallography, catalytic conditions, and computational studies. CCDC 1539832–1539836. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7sc01491k Click here for additional data file. Click here for additional data file. Click here for additional data file.

    Science.gov (United States)

    Chadwick, F. Mark; McKay, Alasdair I.; Martinez-Martinez, Antonio J.; Rees, Nicholas H.; Krämer, Tobias

    2017-01-01

    Single-crystal to single-crystal solid/gas reactivity and catalysis starting from the precursor sigma-alkane complex [Rh(Cy2PCH2CH2PCy2)(η2η2-NBA)][BArF4] (NBA = norbornane; ArF = 3,5-(CF3)2C6H3) is reported. By adding ethene, propene and 1-butene to this precursor in solid/gas reactions the resulting alkene complexes [Rh(Cy2PCH2CH2PCy2)(alkene)x][BArF4] are formed. The ethene (x = 2) complex, [Rh(Cy2PCH2CH2PCy2)(ethene)2][BArF4]-Oct, has been characterized in the solid-state (single-crystal X-ray diffraction) and by solution and solid-state NMR spectroscopy. Rapid, low temperature recrystallization using solution methods results in a different crystalline modification, [Rh(Cy2PCH2CH2PCy2)(ethene)2][BArF4]-Hex, that has a hexagonal microporous structure (P6322). The propene complex (x = 1) [Rh(Cy2PCH2CH2PCy2)(propene)][BArF4] is characterized as having a π-bound alkene with a supporting γ-agostic Rh···H3C interaction at low temperature by single-crystal X-ray diffraction, variable temperature solution and solid-state NMR spectroscopy, as well as periodic density functional theory (DFT) calculations. A fluxional process occurs in both the solid-state and solution that is proposed to proceed via a tautomeric allyl-hydride. Gas/solid catalytic isomerization of d3-propene, H2C 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000

  7. Computation in Dynamically Bounded Asymmetric Systems

    Science.gov (United States)

    Rutishauser, Ueli; Slotine, Jean-Jacques; Douglas, Rodney

    2015-01-01

    Previous explanations of computations performed by recurrent networks have focused on symmetrically connected saturating neurons and their convergence toward attractors. Here we analyze the behavior of asymmetrical connected networks of linear threshold neurons, whose positive response is unbounded. We show that, for a wide range of parameters, this asymmetry brings interesting and computationally useful dynamical properties. When driven by input, the network explores potential solutions through highly unstable ‘expansion’ dynamics. This expansion is steered and constrained by negative divergence of the dynamics, which ensures that the dimensionality of the solution space continues to reduce until an acceptable solution manifold is reached. Then the system contracts stably on this manifold towards its final solution trajectory. The unstable positive feedback and cross inhibition that underlie expansion and divergence are common motifs in molecular and neuronal networks. Therefore we propose that very simple organizational constraints that combine these motifs can lead to spontaneous computation and so to the spontaneous modification of entropy that is characteristic of living systems. PMID:25617645

  8. Unitarity Constraints on Asymmetric Freeze-In

    Energy Technology Data Exchange (ETDEWEB)

    Hook, Anson; /SLAC

    2011-08-15

    This paper considers unitarity and CPT constraints on asymmetric freeze-in, the use of freeze-in to store baryon number in a dark sector. In this scenario, Sakharov's out of equilibrium condition is satisfied by placing the visible and hidden sectors at different temperatures while a net visible baryon number is produced by storing negative baryon number in a dark sector. It is shown that unitarity and CPT lead to unexpected cancellations. In particular, the transfer of baryon number cancels completely at leading order. This note has shown that if two sectors are in thermal equilibrium with themselves, but not with each other, then the leading effect transferring conserved quantities between the two sectors is of order the the weak coupling connecting them to the third power. When freeze-in is used to produce a net baryon number density, the leading order effect comes from {Omicron}({lambda}{sup 3}) diagrams where the intermediate state that goes on-shell has a different visible baryon number than the final state visible baryon number. Models in which the correct baryon number is generated with freeze-in as the dominant source of abundance, typically require {lambda} {approx}> 10{sup -6} and m{sub bath} {approx}> TeV. m{sub bath} is the mass of the visible particle which communicates with the hidden sector. The lower window is potentially observable at the LHC.

  9. Asymmetric iterative blind deconvolution of multiframe images

    Science.gov (United States)

    Biggs, David S. C.; Andrews, Mark

    1998-10-01

    Imaging through a stochastically varying distorting medium, such as a turbulent atmosphere, requires multiple short-exposure frames to ensure maximum resolution of object features. Restoration methods are used to extract the common underlying object from the speckle images, and blind deconvolution techniques are required as typically there is little prior information available about either the image or individual PSFs. A method is presented for multiframe restoration based on iterative blind deconvolution, which alternates between restoring the image and PSF estimates. A maximum-likelihood approach is employed via the Richardson-Lucy (RL) method which automatically ensures positively and conservation of the total number of photons. The restoration is accelerated by applying a vector sequence is treated as a 3D volume of data and processed to produce a 3D stack of PSFs and a single 2D image of the object. The problem of convergence to an undesirable solution, such as a delta function, is addressed by weighting the number of image or PSF iterations according to how quickly each is converging, this leads to the asymmetrical nature of the algorithm. Noise artifacts are suppressed by using a dampened RL algorithm to prevent over fitting of the corrupted data. Results are presented for real single frame and simulated multiframe speckle imaging.

  10. Asymmetric sensory reweighting in human upright stance.

    Directory of Open Access Journals (Sweden)

    David Logan

    Full Text Available To investigate sensory reweighting as a fundamental property of sensor fusion during standing, we probed postural control with simultaneous rotations of the visual scene and surface of support. Nineteen subjects were presented with pseudo-random pitch rotations of visual scene and platform at the ankle to test for amplitude dependencies in the following conditions: low amplitude vision: high amplitude platform, low amplitude vision: low amplitude platform, and high amplitude vision: low amplitude platform. Gain and phase of frequency response functions (FRFs to each stimulus were computed for two body sway angles and a single weighted EMG signal recorded from seven muscles. When platform stimulus amplitude was increased while visual stimulus amplitude remained constant, gain to vision increased, providing strong evidence for inter-modal reweighting between vision and somatosensation during standing. Intra-modal reweighting of vision was also observed as gains to vision decreased as visual stimulus amplitude increased. Such intra-modal and inter-modal amplitude dependent changes in gain were also observed in muscular activity. Gains of leg segment angle and muscular activity relative to the platform, on the other hand, showed only intra-modal reweighting. That is, changing platform motion amplitude altered the responses to both visual and support surface motion whereas changing visual scene motion amplitude did not significantly affect responses to support surface motion, indicating that the sensory integration scheme between somatosensation (at the support surface and vision is asymmetric.

  11. Asymmetric Dark Matter and Dark Radiation

    International Nuclear Information System (INIS)

    Blennow, Mattias; Martinez, Enrique Fernandez; Mena, Olga; Redondo, Javier; Serra, Paolo

    2012-01-01

    Asymmetric Dark Matter (ADM) models invoke a particle-antiparticle asymmetry, similar to the one observed in the Baryon sector, to account for the Dark Matter (DM) abundance. Both asymmetries are usually generated by the same mechanism and generally related, thus predicting DM masses around 5 GeV in order to obtain the correct density. The main challenge for successful models is to ensure efficient annihilation of the thermally produced symmetric component of such a light DM candidate without violating constraints from collider or direct searches. A common way to overcome this involves a light mediator, into which DM can efficiently annihilate and which subsequently decays into Standard Model particles. Here we explore the scenario where the light mediator decays instead into lighter degrees of freedom in the dark sector that act as radiation in the early Universe. While this assumption makes indirect DM searches challenging, it leads to signals of extra radiation at BBN and CMB. Under certain conditions, precise measurements of the number of relativistic species, such as those expected from the Planck satellite, can provide information on the structure of the dark sector. We also discuss the constraints of the interactions between DM and Dark Radiation from their imprint in the matter power spectrum

  12. Climate policy, asymmetric information and firm survival

    International Nuclear Information System (INIS)

    Hagem, C.

    2001-02-01

    The purpose of this paper is to compare the effect of different domestic climate policy instruments under asymmetric information when the regulator wants to secure the survival of a specific firm. It is a well-known result from economic theory that emission taxes lead to a cost-effective distribution of abatement across polluters. However, if the regulator wants to ensure the survival of a specific firm, it may need to design policy instruments that reduce the firm's cost of complying with an emission tax regime. The climate policy instruments considered in this paper are tradable emission permits with distribution of free permits, emission taxes in combination with a fixed subsidy, and two types of voluntary agreements. It demonstrates first that if distributing free tradable permits shall have a preventing effect, the allocation of permits has to be made contingent on production. It further shows that a voluntary agreement where a specific abatement target is set by the regulator can prevent a shutdown but leads to lower welfare than the use of emission taxes in combination with a fixed subsidy. And finally it illustrates that a voluntary agreement designed as a menu of abatement contracts increases social welfare compared to an emission tax regime

  13. Network effects on coordination in asymmetric games.

    Science.gov (United States)

    Broere, Joris; Buskens, Vincent; Weesie, Jeroen; Stoof, Henk

    2017-12-05

    Network structure can have an important effect on the behavior of players in an iterated 2 × 2 game. We study the effect of network structure on global and local behavior in asymmetric coordination games using best response dynamics. We find that global behavior is highly dependent on network topology. Random (Erdös-Rényi) networks mostly converge to homogeneous behavior, but the higher the clustering in the network the more heterogeneous the behavior becomes. Behavior within the communities of the network is almost exclusively homogeneous. The findings suggest that clustering of networks facilitates self-organization of uniform behavior within clusters, but heterogeneous behavior between clusters. At the local level we find that some nodes are more important in determining the equilibrium behavior than other nodes. Degree centrality is for most networks the main predictor for the behavior and nodes with an even degree have an advantage over nodes with an uneven degree in dictating the behavior. We conclude that the behavior is difficult to predict for (Erdös-Rényi) networks and that the network imposes the behavior as a function of clustering and degree heterogeneity in other networks.

  14. Asymmetric translation between multiple representations in chemistry

    Science.gov (United States)

    Lin, Yulan I.; Son, Ji Y.; Rudd, James A., II

    2016-03-01

    Experts are more proficient in manipulating and translating between multiple representations (MRs) of a given concept than novices. Studies have shown that instruction using MR can increase student understanding of MR, and one model for MR instruction in chemistry is the chemistry triplet proposed by Johnstone. Concreteness fading theory suggests that presenting concrete representations before abstract representations can increase the effectiveness of MR instruction; however, little work has been conducted on varying the order of different representations during instruction and the role of concreteness in assessment. In this study, we investigated the application of concreteness fading to MR instruction and assessment in teaching chemistry. In two experiments, undergraduate students in either introductory psychology courses or general chemistry courses were given MR instruction on phase changes using different orders of presentation and MR assessment questions based on the representations in the chemistry triplet. Our findings indicate that the order of presentation based on levels of concreteness in MR chemistry instruction is less important than implementation of comprehensive MR assessments. Even after MR instruction, students display an asymmetric understanding of the chemical phenomenon on the MR assessments. Greater emphasis on MR assessments may be an important component in MR instruction that effectively moves novices toward more expert MR understanding.

  15. Experimental study of asymmetric heart valve prototype

    Science.gov (United States)

    Vukicevic, M.; Fortini, S.; Querzoli, G.; Cenedese, A.; Pedrizzetti, G.

    2011-11-01

    The mechanical heart valves (MHVs) are extremely important medical devices, commonly used for diseased heart valves replacement. Despite the long term of use and constant design refinement, the MHVs are very far from ideal and their performance is very diverse from that of the native ones. It has been approved that small variations in geometry of valvular leaflets influence the significant change in the intraventricular vortical flow, known as one of the most important factors for the overall functionality of the heart. We have experimentally examined the home-made heart valve prototypes, exclusively modeled for the mitral valve replacement. The performance and energetic properties of the prototypes have been compared with those in the presence of standard MHVs. The analysis was based on the testing of intraventricular fluid dynamics, usually missing criteria for the quality of the valve performance. It has been shown that the asymmetric prototype, with unequal leaflets and D-shaped orifice produces flow patterns and energetic properties close to those found in the healthy subjects. Thus, the break of symmetry in the standard bi-leaflet MHV prosthesis, at least from the fluid dynamics point of view, is worthwhile to be considered for the design of MHVs for the mitral valve replacement.

  16. Collaborative hierarchy maintains cooperation in asymmetric games.

    Science.gov (United States)

    Antonioni, Alberto; Pereda, María; Cronin, Katherine A; Tomassini, Marco; Sánchez, Angel

    2018-03-29

    The interplay of social structure and cooperative behavior is under much scrutiny lately as behavior in social contexts becomes increasingly relevant for everyday life. Earlier experimental work showed that the existence of a social hierarchy, earned through competition, was detrimental for the evolution of cooperative behaviors. Here, we study the case in which individuals are ranked in a hierarchical structure based on their performance in a collective effort by having them play a Public Goods Game. In the first treatment, participants are ranked according to group earnings while, in the second treatment, their rankings are based on individual earnings. Subsequently, participants play asymmetric Prisoner's Dilemma games where higher-ranked players gain more than lower ones. Our experiments show that there are no detrimental effects of the hierarchy formed based on group performance, yet when ranking is assigned individually we observe a decrease in cooperation. Our results show that different levels of cooperation arise from the fact that subjects are interpreting rankings as a reputation which carries information about which subjects were cooperators in the previous phase. Our results demonstrate that noting the manner in which a hierarchy is established is essential for understanding its effects on cooperation.

  17. Asymmetric evaluation promotes cooperation in network population

    Science.gov (United States)

    Shen, Chen; Li, Xiaoping; Shi, Lei; Deng, Zhenghong

    2017-05-01

    The evolution of cooperation remains a fundamental challenge in human society. Many previous studies investigated these questions via spatial reciprocity, where players obtain their payoffs by interacting with their direct neighbors. It has also been verified that environmental factors can influence the evolution of cooperation theoretically and empirically. In reality, however, individuals may have the limit knowledge about their indirect neighbors. Inspired by this fact, we consider an asymmetric fitness calculation mechanism, which only integrates the environment factors into the focal player, to explore the evolution of cooperation. Here, the environmental factor is defined as the average payoff of all individual neighbors, which is regulated by a tunable parameter u. Through numerical simulation, we find that, compared with the traditional version (u = 0), that the cooperation level can be greatly enhanced when u is positive. Interestingly, the larger the value of u, the higher the level of cooperation. Finally, to explore the generality of this finding, we have tested the results on different topologies.

  18. CATALYTIC SPECTROPHOTOMETRIC DETERMINATION OF Mn(II ...

    African Journals Online (AJOL)

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    The aim of the present study was to develop a new precise and accurate catalytic spectrophotometric ... manganese sulfate monohydrate (Merck, Darmstadt, Germany) in water and diluted to 250 mL. The working .... and potassium hydrogen phthalate-HCl buffer solutions, the slope of calibration graph was unsatisfactory.

  19. Catalytic models developed through social work

    DEFF Research Database (Denmark)

    Jensen, Mogens

    2015-01-01

    of adolescents placed in out-of-home care and is characterised using three situated cases as empirical data. Afterwards the concept of catalytic processes is briefly presented and then applied in an analysis of pedagogical treatment in the three cases. The result is a different conceptualisation of the social...

  20. Fluid catalytic cracking : Feedstocks and reaction mechanism

    NARCIS (Netherlands)

    Dupain, X.

    2006-01-01

    The Fluid Catalytic Cracking (FCC) process is one of the key units in a modern refinery. Traditionally, its design is primarily aimed for the production of gasoline from heavy oil fractions, but as co-products also diesel blends and valuable gasses (e.g. propene and butenes) are formed in