Sample records for stable p-heterocyclic carbenes

  1. Cyclic (alkyl)(amino)carbenes (CAACs): stable carbenes on the rise.

    PubMed

    Soleilhavoup, Michèle; Bertrand, Guy

    2015-02-17

    CONSPECTUS: Carbenes are compounds that feature a divalent carbon atom with only six electrons in its valence shell. In the singlet state, they possess a lone pair of electrons and a vacant orbital and therefore exhibit Lewis acidic and Lewis basic properties, which explains their very high reactivity. Following the preparation by our group in 1988 of the first representative, a variety of stable carbenes are now available, the most popular being the cyclic diaminocarbenes. In this Account, we discuss another class of stable cyclic carbenes, namely, cyclic (alkyl)(amino)carbenes (CAACs), in which one of the electronegative and ?-donor amino substituents of diaminocarbenes is replaced by a ?-donating but not ?-donating alkyl group. As a consequence, CAACs are more nucleophilic (?-donating) but also more electrophilic (?-accepting) than diaminocarbenes. Additionally, the presence of a quaternary carbon in the position ? to the carbene center provides steric environments that differentiate CAACs dramatically from all other ligands. We show that the peculiar electronic and steric properties of CAACs allow for the stabilization of unusual diamagnetic and paramagnetic main group element species. As examples, we describe the preparation of room temperature stable phosphorus derivatives in which the heteroatom is in the zero oxidation state, nucleophilic boron compounds, and phosphorus-, antimony-, boron-, silicon-, and even carbon-centered neutral and cationic radicals. CAACs are also excellent ligands for transition metal complexes. The most recent application is their use for the stabilization of paramagnetic complexes, in which the metal is often in a formal zero oxidation state. Indeed, bis(CAAC)M complexes in which the metal is gold, copper, cobalt, iron, nickel, manganese, and zinc have been isolated. Depending on the metal, the majority of spin density can reside either on the metal or on the carbene carbons and the nitrogen atoms of the CAAC ligand. In contrast to diaminocarbenes, the higher basicity of CAACs makes them poor leaving groups, and thus they cannot be used for classical organocatalysis. However, because of their superior electrophilicity and smaller singlet-triplet gap, CAACs can activate small molecules at room temperature, such as CO, H2, and P4, as well as enthalpically strong bonds, such as B-H, Si-H, N-H, and P-H. Lastly, excellent results have been obtained in palladium, ruthenium, and gold catalysis. CAAC-metal complexes are extremely thermally robust, which allows for their utilization in harsh conditions. This property has been used to perform a variety of gold-catalyzed reactions in the presence of basic amines, including ammonia and hydrazine, which usually deactivate catalysts. PMID:25515548

  2. A Stable Planar-Chiral N-Heterocyclic Carbene with a 1,1'-Ferrocenediyl Backbone.

    PubMed

    Petrov, Alex R; Derheim, Anatoli; Oetzel, Jan; Leibold, Michael; Bruhn, Clemens; Scheerer, Stefan; Oßwald, Steffen; Winter, Rainer F; Siemeling, Ulrich

    2015-07-01

    This paper focuses on the stable, ferrocene-based N-heterocyclic carbene (NHC) rac-[Fe{(?(5)-t-BuC5H3)NpN}2C:] (A'-Np, Np = neopentyl), which is planar-chiral due to the two tert-butyl substituents in 3,3'-positions. A'-Np was synthesized in nine steps starting from 1,1'-di-tert-butylferrocene (1), the first step being its 3,3'-dilithiation to afford rac-[Fe(?(5)-t-BuC5H3Li)2] (rac-fc'Li2, 2). The structures of rac-fc'(SiMe3)2 (3), rac-fc'Br2 (4), rac-fc'(N3)2 (5), and the immediate carbene precursor [A'-NpH]BF4 were determined by single-crystal X-ray diffraction (XRD). The chemical properties of A'-Np were found to be very similar to those of its tert-butyl-free congener A-Np, both being ambiphilic NHCs with rather high calculated HOMO energies (ca. -4.0 eV) and low singlet-triplet gaps (ca. 35 kcal/mol). A Tolman electronic parameter value of 2050 cm(-1) was derived from IR data of cis-[RhCl(A'-Np)(CO)2], indicating the high donicity of A'-Np as a ligand. Consistent with its ambiphilic nature, A'-Np was found to react readily with carbon monoxide, affording the betainic enolate (A'-Np)2CO as four stereoisomers, viz. (RpRp-A'-Np)?C(O(-))(RpRp-A'-Np(+)), (SpSp-A'-Np)?C(O(-))(SpSp-A'-Np(+)), (RpRp-A'-Np)?C(O(-))(SpSp-A'-Np(+)), and (SpSp-A'-Np)?C(O(-))(RpRp-A'-Np(+)). The former two isomers were structurally characterized as a racemic compound by single-crystal XRD. A'-Np was found to react swiftly with dichloromethane, affording the addition product A'-NpH-CHCl2 in a reaction that is unprecedented for diaminocarbenes. A-NpH-CHCl2 was obtained analogously. Both compounds were structurally characterized by single-crystal XRD. An electrochemical investigation of A'-Np by cyclic and square wave voltammetry revealed a reversible oxidation of the carbene at a half-wave potential of -0.310 vs ferrocene/ferrocenium (THF/NBu4PF6). The electrochemical data previously published for A-Np were identified to be incorrect, since unnoticed hydrolysis of the NHC had taken place, affording A-Np(H2O). The hydrolysis products of A-Np and A'-Np were found to be reversibly oxidized at half-wave potentials of -0.418 and -0.437 V, respectively. PMID:26098133

  3. Redox and luminescent properties of robust and air-stable N-heterocyclic carbene group 4 metal complexes.

    PubMed

    Romain, Charles; Choua, Sylvie; Collin, Jean-Paul; Heinrich, Martine; Bailly, Corinne; Karmazin-Brelot, Lydia; Bellemin-Laponnaz, Stéphane; Dagorne, Samuel

    2014-07-21

    Robust and air-stable homoleptic group 4 complexes of the type M(L)2 [1-3; M = Ti, Zr, Hf; L = dianionic bis(aryloxide) N-heterocyclic carbene (NHC) ligand] were readily synthesized from the NHC proligand 1,3-bis(3,5-di-tert-butyl-2-hydroxyphenyl)imidazolinium chloride (H3L,Cl) and appropriate group 4 precursors. As deduced from cyclic voltammetry studies, the homoleptic bis-adduct zirconium and hafnium complexes 2 and 3 can also be oxidized, with up to four one-electron-oxidation signals for the zirconium derivative 2 (three reversible signals). Electron paramagnetic resonance data for the one-electron oxidation of complexes 1-3 agree with the formation of ligand-centered species. Compounds 2 and 3 are luminescent upon excitation in the absorption band at 362 nm with emissions at 485 and 534 nm with good quantum yields (? = 0.08 and 0.12) for 2 and 3, respectively. In contrast, the titanium complex 1 does not exhibit luminescent properties upon excitation in the absorption band at 310 and 395 nm. Complexes 2 and 3 constitute the first examples of emissive nonmetallocene group 4 metal complexes. PMID:24957272

  4. Moving toward Ylide-Stabilized Carbenes.

    PubMed

    Borthakur, Bitupon; Phukan, Ashwini K

    2015-08-01

    The effect of ylide substitution at the ? position to the carbene carbon (Cc ) atom on the stability and ?-donating ability of a number of cyclic carbenes has been studied theoretically. The stabilities of all of the carbenes were investigated from an evaluation of their singlet-triplet energy gaps and stabilization energies. All carbenes were found to have a stable singlet state. The energy of the ?-symmetric lone-pair orbital at the Cc atom increases as a result of the introduction of ylide centers near to the Cc atom. This indicates an enhanced ?-donating ability of the ylide-containing carbenes. The calculated carbonyl-stretching frequencies of the corresponding rhodium complexes, proton affinities, and nucleophilicity index values correlate well with the ? basicity of the carbenes. PMID:26119685

  5. Synthesis of a Simplified Version of Stable Bulky and Rigid Cyclic (Alkyl)(Amino)Carbenes (CAACs), and Catalytic Activity of the Ensuing Gold(I) Complex in the Three-Component Preparation of 1,2-Dihydroquinoline Derivatives

    PubMed Central

    Zeng, Xiaoming; Frey, Guido D.; Kinjo, Rei; Donnadieu, Bruno; Bertrand, Guy

    2009-01-01

    A 95/5 mixture of cis and trans 2,4-dimethyl-3-cyclohexenecarboxaldehyde (trivertal), a common fragrance and flavor material produced in bulk quantities, serves as the precursor for the synthesis of a stable spirocyclic (alkyl)(amino)carbene, in which the 2-methyl-substituted cyclohexenyl group provides steric protection to an ensuing metal. The efficiency of this carbene as ligand for transition metal based catalysts is first illustrated by the gold(I) catalyzed hydroamination of internal alkynes with secondary dialkyl amines, a process with little precedent. The feasibility of this reaction allows for significantly enlarging the scope of the one-pot three-component synthesis of 1,2-dihydroquinoline derivatives, and related nitrogen-containing heterocycles. Indeed, two different alkynes were used, which include an internal alkyne for the first step. PMID:19456108

  6. Synthesis of a simplified version of stable bulky and rigid cyclic (alkyl)(amino)carbenes, and catalytic activity of the ensuing gold(I) complex in the three-component preparation of 1,2-dihydroquinoline derivatives.

    PubMed

    Zeng, Xiaoming; Frey, Guido D; Kinjo, Rei; Donnadieu, Bruno; Bertrand, Guy

    2009-06-24

    A 95/5 mixture of cis and trans 2,4-dimethyl-3-cyclohexenecarboxaldehyde (trivertal), a common fragrance and flavor material produced in bulk quantities, serves as the precursor for the synthesis of a stable spirocyclic (alkyl)(amino)carbene, in which the 2-methyl-substituted cyclohexenyl group provides steric protection to an ensuing metal. The efficiency of this carbene as ligand for transition metal based catalysts is first illustrated by the gold(I) catalyzed hydroamination of internal alkynes with secondary dialkyl amines, a process with little precedent. The feasibility of this reaction allows for significantly enlarging the scope of the one-pot three-component synthesis of 1,2-dihydroquinoline derivatives, and related nitrogen-containing heterocycles. Indeed, two different alkynes were used, which include an internal alkyne for the first step. PMID:19456108

  7. Carbene complexes in catalysis

    NASA Astrophysics Data System (ADS)

    Moiseev, Ilya I.

    1989-07-01

    The methods for forming carbene complexes in catalysis are analysed in the case of the catalytic conversions of hydrocarbons, acids, carbonyl compounds, carbon monoxide, and methanol. The bibliography includes 85 references.

  8. Dihydrogen activation by frustrated carbene-borane Lewis pairs: an experimental and theoretical study of carbene variation.

    PubMed

    Kronig, Sabrina; Theuergarten, Eileen; Holschumacher, Dirk; Bannenberg, Thomas; Daniliuc, Constantin G; Jones, Peter G; Tamm, Matthias

    2011-08-01

    A variety of Lewis acid-base pairs consisting of tris(pentafluorophenyl)borane, B(C(6)F(5))(3), in combination with sterically demanding five- and six-membered N-heterocyclic carbenes (NHCs) of the imidazolin-2-ylidene, imidazolidin-2-ylidene, and tetrahydropyrimidin-2-ylidene types were investigated with respect to their potential to act as frustrated Lewis pairs (FLP) by reaction with dihydrogen (H(2)) and tetrahydrofuran (THF). A sufficient degree of "frustration" was usually established by introduction of a 1,3-di-tert-butyl or 1,3-diadamantyl carbene substitution pattern, which allows an unquenched acid-base reactivity and thus leads to heterolytic dihydrogen activation and ring-opening of THF. In contrast, 1,3-bis(2,6-diisopropylphenyl)-substituted carbenes showed ambiguous behavior, and the corresponding five-membered imidazolin-2-ylidene formed a stable carbene-B(C(6)F(5))(3) adduct, whereas fast C-F activation and formation of a zwitterionic pyrimidinium-fluoroborate was observed for the six-membered tetrahydropyrimidin-2-ylidene. A stable adduct was also isolated for the combination of the acyclic carbene bis(diisopropylamino)methylene with B(C(6)F(5))(3), and consequently no reactivity toward H(2) and THF was observed. To rationalize the reactivity of the carbene-borane Lewis pairs, the thermodynamics of adduct formation with B(C(6)F(5))(3) were calculated for 10 different carbenes; the stability (or instability) of these adducts can be used as a good measure of the degree of "frustration". PMID:21718018

  9. Synthesis and Properties of Chelating N-Heterocyclic Carbene Rhodium(I) Complexes: Synthetic Experiments in Current Organometallic Chemistry

    ERIC Educational Resources Information Center

    Mata, Jose A.; Poyatos, Macarena; Mas-Marza, Elena

    2011-01-01

    The preparation and characterization of two air-stable Rh(I) complexes bearing a chelating N-heterocyclic carbene (NHC) ligand is described. The synthesis involves the preparation of a Ag(I)-NHC complex and its use as carbene transfer agent to a Rh(I) precursor. The so obtained complex can be further reacted with carbon monoxide to give the…

  10. Substitution effects on the formation of T-shaped palladium carbene and thioketone complexes from Li/Cl carbenoids.

    PubMed

    Molitor, Sebastian; Feichtner, Kai-Stephan; Kupper, Claudia; Gessner, Viktoria H

    2014-08-18

    The preparation of palladium thioketone and T-shaped carbene complexes by treatment of thiophosphoryl substituted Li/Cl carbenoids with a Pd(0) precursor is reported. Depending on the steric demand, the anion-stabilizing ability of the silyl moiety (by negative hyperconjugation effects) and the remaining negative charge at the carbenic carbon atom, isolation of a three-coordinate, T-shaped palladium carbene complex is possible. In contrast, insufficient charge stabilization results in the transfer of the sulfur of the thiophosphoryl moiety and thus in the formation of a thioketone complex. While the thioketones are stable compounds the carbene complexes are revealed to be highly reactive and decompose under elimination of Pd metal. Computational studies revealed that both complexes are formed by a substitution mechanism. While the ketone turned out to be the thermodynamically favored product, the carbene is kinetically favored and thus preferentially formed at low reaction temperatures. PMID:24664573

  11. Gold-catalyzed carbene transfer reactions.

    PubMed

    Shin, Seunghoon

    2015-01-01

    In homogeneous gold catalysis, generations and reactions of metal carbenes have been one of the most rapidly developing areas because of their diverse reactivity under mild conditions. This review covers recent advances in the gold-catalyzed oxygen atom transfer and carbene transfer reactions to alkynes. Atom transfer to an alkyne enables alkynes to function as metal carbene synthons. Many such reactions fulfill redox neutrality starting from safe and easily handled precursors. PMID:25518973

  12. Computational Chemistry Studies on the Carbene Hydroxymethylene

    ERIC Educational Resources Information Center

    Marzzacco, Charles J.; Baum, J. Clayton

    2011-01-01

    A density functional theory computational chemistry exercise on the structure and vibrational spectrum of the carbene hydroxymethylene is presented. The potential energy curve for the decomposition reaction of the carbene to formaldehyde and the geometry of the transition state are explored. The results are in good agreement with recent…

  13. The reactivity game: theoretical predictions for heavy atom tunneling in adamantyl and related carbenes.

    PubMed

    Kozuch, S

    2014-05-01

    The possibility of carbon atom tunneling at cryogenic temperatures for carbene-based ring expansion of adamantane analogues calls for a delicate balance of reactivity to experimentally detect the transpiring reaction. An overly reactive carbene will precipitously decay; an excessively stable carbene will not tunnel. Nevertheless, the factors that affect the quantum-mechanical tunneling (QMT) reactivity - mass, barrier height and width - are strikingly different from the classical "over the barrier" thermal mechanism. Herein, comparisons with experimental values and predictions on measurable rate constants for novel carbene systems are presented by way of small curvature tunneling (SCT) computations. Adamantane, noradamantane and bisnoradamantane have a significantly different C-C bond strain and reactivity, which can be modulated by tinkering with the carbene substituent atom (H, Cl or F) to obtain an observable lifetime of the reactant. The influence of barrier heights and widths, kinetic isotope effects (KIEs), the detection of the tunneling-determining atoms (TDA) and the comparisons with hydrogen-based reactions are discussed with the objective of finding the physical limits for QMT. PMID:24590008

  14. Carbene transfer from triazolylidene gold complexes as a potent strategy for inducing high catalytic activity.

    PubMed

    Canseco-Gonzalez, Daniel; Petronilho, Ana; Mueller-Bunz, Helge; Ohmatsu, Kohsuke; Ooi, Takashi; Albrecht, Martin

    2013-09-01

    A series of gold(I) complexes [AuCl(trz)] were synthesized that contain 1,2,3-triazolylidene (trz) ligands with variable wingtip groups. In the presence of AgBF4, these complexes undergo ligand redistribution to yield cationic complexes [Au(trz)2]BF4 in high yields as a result of efficient carbene transfer. Identical reactivity patterns were detected for carbene gold complexes comprised of Arduengo-type IMes ligands (IMes = N,N'-dimesityl-imidazol-2-ylidene). Reaction of cationic complexes [Au(trz)2](+) with [AuCl(trz')] afforded the heteroleptic complex [Au(trz)(trz')](+) and [AuCl(trz)] (trz, trz' = triazolylidene ligands with different wingtip groups). Carbene transfer occurs spontaneously, yet is markeldy rate-enhanced in the presence of Ag(+). The facile carbene transfer was exploited as a catalyst activation process to form active gold species for the aldol condensation of isocyanides and aldehydes to form oxazolines. The catalytic activity is strongly dependent on the presence of Ag(+) ions to initiate catalyst activation. High turnovers (10(5)) and turnover frequencies (10(4) h(-1)) were accomplished. Structural analysis at early stages of the reaction support the critical role of triazolylidene dissociation to activate the precatalyst and dynamic light scattering revealed the presence of nanoparticles (±100 nm diameter) as potential catalytically active species. Furthermore, the triazolylidene scaffold had no impact on the diastereoselectivity of the oxazoline formation, and chiral triazolylidenes did not induce any asymmetry in the product. The facile dissociation of carbenes from [AuCl(carbene)] in the presence of Ag(+) ions suggests a less stable Au-Ccarbene interaction than often assumed, with potential implications for gold-catalyzed reactions that employ a silver salt as (putative) halide scavenger. PMID:23902160

  15. Nucleophilic ?-Carbon Activation of Propionic Acid as a 3-Carbon Synthon by Carbene Organocatalysis.

    PubMed

    Jin, Zhichao; Jiang, Ke; Fu, Zhenqian; Torres, Jaume; Zheng, Pengcheng; Yang, Song; Song, Bao-An; Chi, Yonggui Robin

    2015-06-22

    Direct ?-carbon activation of propionic acid (C2 H5 CO2 H) by carbene organocatalysis has been developed. This activation affords the smallest azolium homoenolate intermediate (without any substituent) as a 3-carbon nucleophile for enantioselective reactions. Propionic acid is an excellent raw material because it is cheap, stable, and safe. This approach provides a much better solution to azolium homoenolate synthesis than the previously established use of acrolein (enal without any substituent), which is expensive, unstable, and toxic. PMID:26013883

  16. On the organocatalytic activity of N-heterocyclic carbenes: role of sulfur in thiamine.

    PubMed

    Hollóczki, Oldamur; Kelemen, Zsolt; Nyulászi, László

    2012-07-20

    The reaction energy profiles of the benzoin condensation from three aldehydes catalyzed by imidazol-2-ylidene, triazol-3-ylidene, and thiazol-2-ylidene have been investigated computationally. The barriers for all steps of all investigated reactions have been found to be low enough to indicate the viability of the mechanism proposed by Breslow in the 1950s. The most remarkable difference in the catalytic cycles has been the increased stability of the Breslow intermediate in case of thiazol-2-ylidene (by ca. 10 kcal/mol) compared to the other two carbenes, which results in lower energy for the coupling of the second aldehyde molecule, thus, increasing the reversibility of the reaction. Since the analogous transketolase reaction, being involved in the carbohydrate metabolism of many organisms, requires an initial decoupling-a reverse benzoin condensation-this difference provides a reasonable explanation for the presence of a thiazolium ring in thiamine instead of the otherwise generally more available imidazole derivatives. The "resting intermediate" found by Berkessel and co-workers for a triazole-based catalyst was found more stable than the Breslow intermediate for all of the systems investigated. The (gas phase) proton affinities of several carbenes were compared, the relative trends being in agreement with the available (in aqueous solution) data. The hydrolytic ring-opening reaction of the thiazole-based carbene was shown to be different from that of imidazole-2-ylidenes. PMID:22731396

  17. Protonation of Homoenolate Equivalents Generated by N-Heterocyclic Carbenes

    PubMed Central

    Maki, Brooks E.; Chan, Audrey; Scheidt, Karl A.

    2010-01-01

    Homoenolate equivalents are generated by Lewis basic N-heterocyclic carbene catalysts and then protonated to generate efficiently saturated esters from unsaturated aldehydes. This reactivity is extended to the generation of ?-acylvinyl anions from alkynyl aldehydes. The asymmetric protonation of a homoenolate equivalent generated from a ?,?-disubstituted aldehyde can be accomplished with a chiral N-heterocyclic carbene. PMID:22347730

  18. N-Heterocyclic Carbene-Catalyzed Conjugate Additions of Alcohols

    PubMed Central

    Phillips, Eric M.; Riedrich, Matthias; Scheidt, Karl A.

    2010-01-01

    An efficient intermolecular conjugate addition of alcohols to activated alkenes catalyzed by N-heterocyclic carbenes has been developed. With 5 mol % of the free carbene derived from IMes•HCl, unsaturated ketones and esters are competent substrates and a variety of primary and secondary alcohols can be employed as the nucleophile. No oligomerization is observed under these mild conditions for effective hydroalkoxylation. In addition to reactions with activated alkenes, IMes catalyzes the formation of vinyl ethers through the 1,4-addition of alcohols to ynones and promotes tandem conjugate addition/Michael cascade reactions. Preliminary data supports a Brønsted base mechanism with the free carbene. PMID:20809579

  19. Chemistry of transition metal carbene complexes: nucleophilic substitution reactions of cyanamide anion to Fischer carbene complexes.

    PubMed

    Gangopadhyay, Sumana; Mistri, Tarun; Dolai, Malay; Alam, Rabiul; Ali, Mahammad

    2013-01-14

    Rate constants for the reactions of cyanamide anion N?C-NH(-) with Fischer carbene complexes of the type (CO)(5)M=C(XR)C(6)H(4)Z with M = Cr and W, XR = SMe and OMe, Z = NMe(2), OMe, Me, H, F, Cl and CF(3) in 50% MeCN-50% water (v/v) at 25 °C are reported. N?C-NH(-) shows a much higher reactivity towards these carbene complexes than OH(-), primary aliphatic amines (e.g. n-butylamine) or secondary alicyclic amines (e.g. piperidine) but is slightly less reactive than thiolate ions (e.g. HOCH(2)CH(2)S(-)). The alkoxy carbene complexes were found to react faster than the thiomethyl derivatives, consistent with previous findings for alkoxide ion, CH(CN)(2)(-), OH(-), amine and thiolate ion nucleophiles. Hammett ? values are 3.00 ± 0.08 (k(1)) and 2.98 ± 0.08 (k(2)) for Cr-OMe-Z-N?C-NH(-) reactions and 0.94 ± 0.05 (k(1)) for Cr-SMe-Z-N?C-NH(-) reactions. The ? values for the reaction of Cr-OMe-Z and Cr-SMe-Z with CH(CN)(2)(-) and DABCO (1,4-diazabicyclo[2.2.2]octane) (in 50% MeCN-50% H(2)O (v/v) are comparable to the present reactions. The much higher reactivity and hence much higher ? value for methoxy carbene complexes over the corresponding thiomethyl derivatives is best explained by considering the substituent effects not only on the transition state (TS) but also on the reactant, and consistent with the previously observed pattern. Higher k(1)(W)/k(1)(Cr) ratios for (thiomethyl)carbene complexes as well as methoxy and ethoxycarbene complexes are related to the intrinsic rate constant which is higher for tungsten-carbene complexes than the corresponding Cr ones resulting in an enhanced ratio. This can also be explained by considering the electronegativity of Cr and W, which is higher for the latter; as a result the negative charge on the central metal atom is more localized in case of W causing destabilization of the TS and hence higher reactivity. PMID:23076623

  20. Carbenes As Catalysts for Transformations of Organometallic Iron Complexes

    PubMed Central

    Lavallo, Vincent; Grubbs, Robert H.

    2010-01-01

    Compared with the enormous arsenal of catalysts used to produce organic compounds, complementary species that are able to mediate sophisticated organometallic transformations are virtually nonexistent. We found that stable N-heterocyclic carbenes (NHCs) can mediate unusual organometallic transformations in solution at room temperature. Depending on the choice of NHC initiator, stoichiometric or catalytic reactions of bis(cyclooctatetraene)iron [Fe(COT)2] ensue. The stoichiometric reaction leads to the isolation of a previously unknown mixed-valent species, featuring distinct and directly bonded Fe(0) and Fe(I) centers. In the catalytic process, three iron atoms are fused to afford the tri-iron cluster Fe3(COT)3, which is a hydrocarbon analog of Dewar’s classic Fe3(CO)12 complex. The key step in both of these processes is proposed to involve the NHC’s ability to induce metal–metal bond formation. These NHC-mediated reactions provide a foundation on which to develop future organometallic transformations that are catalyzed by organic species. PMID:19900894

  1. Preparation and use of carbonyl-decorated carbenes in the activation of white phosphorus.

    PubMed

    Torres, Antonio J; Dorsey, Christopher L; Hudnall, Todd W

    2014-01-01

    Here we present a protocol for the synthesis of two distinct carbonyl-decorated carbenes. Both carbenes can be prepared using nearly identical procedures in multi-gram scale quantities. The goal of this manuscript is to clearly detail how to handle and prepare these unique carbenes such that a synthetic chemist of any skill level can work with them. The two carbenes described are a diamidocarbene (DAC, carbene 1) and a monoamidoaminocarbene (MAAC 2). These carbenes are highly electron-deficient and as such display reactivity profiles that are atypical of more traditional N-heterocyclic carbenes. Additionally, these two carbenes only differ in their electrophilic character and not their steric parameters, making them ideal for studying how carbene electronics influence reactivity. To demonstrate this phenomenon, we are also describing the activation of white phosphorus (P4) using these carbenes. Depending on the carbene used, two very different phosphorus-containing compounds can be isolated. When the DAC 1 is used, a tris(phosphaalkenyl)phosphane can be isolated as the exclusive product. Remarkably however, when MAAC 2 is added to P4 under identical reaction conditions, an unexpected carbene-supported P8 allotrope of phosphorus is isolated exclusively. Mechanistic studies demonstrate that this carbene-supported P8allotrope forms via a [2+2] cycloaddition dimerization of a transient diphosphene which has been trapped by treatment with 2,3-dimethyl-1,3-butadiene. PMID:25350272

  2. 1,2-Migration in Rhodium(II) Carbene Transfer Reaction: Remarkable Steric Effect on

    E-print Network

    Wang, Jianbo

    1,2-Migration in Rhodium(II) Carbene Transfer Reaction: Remarkable Steric Effect on Migratory the steric effect in 1,2-migration reaction of rhodium(II) carbene. Through the investigation on the diazo effect of the substituent. 1,2-Migration represents a fundamental reaction pathway for both free carbenes

  3. Heterogeneously Substituted Radicals and Carbenes: Photoelectron Imaging of the FC(H)CN-

    E-print Network

    Sanov, Andrei

    Heterogeneously Substituted Radicals and Carbenes: Photoelectron Imaging of the FC(H)CN- and FCCN in the studies of heterogeneous substitution effects in cyanohalo radicals and carbenes. Negative-ion photoelectron imaging was used to investigate the substituted radical and carbene derivatives

  4. Enantioselective N-heterocyclic carbene-catalyzed synthesis of trifluoromethyldihydropyridinones.

    PubMed

    Wang, Dong-Ling; Liang, Zhi-Qin; Chen, Kun-Quan; Sun, De-Qun; Ye, Song

    2015-06-01

    The enantioselective N-heterocyclic carbene-catalyzed [4 + 2] cyclocondensation of ?-chloroaldehydes and trifluoromethyl N-Boc azadienes was developed, giving the corresponding 3,4-disubstituted-6-trifluoromethyldihydropyridin-2(1H)-ones in good yields with exclusive cis-selectivities and excellent enantioselectivities. PMID:25933360

  5. Mechanism of Rhodium-Catalyzed Carbene Formation from Diazo

    E-print Network

    Wang, Jianbo

    Mechanism of Rhodium-Catalyzed Carbene Formation from Diazo Compounds Freeman M. Wong, Jianbo WangVersity, Logan, Utah 84322, and Key Laboratory of Bioorganic Chemistry and Molecular Engineering of the Ministry of Education, College of Chemistry, Peking UniVersity, Beijing, China hengge@mail.usu.edu; wuw

  6. Bis-N-heterocyclic Carbene Aminopincer Ligands Enable High Activity in Ru-Catalyzed Ester Hydrogenation.

    PubMed

    Filonenko, Georgy A; Aguila, Mae Joanne B; Schulpen, Erik N; van Putten, Robbert; Wiecko, Jelena; Müller, Christian; Lefort, Laurent; Hensen, Emiel J M; Pidko, Evgeny A

    2015-06-24

    Bis-N-heterocyclic carbene (NHC) aminopincer ligands were successfully applied for the first time in the catalytic hydrogenation of esters. We have isolated and characterized a well-defined catalyst precursor as a dimeric [Ru2(L)2Cl3]PF6 complex and studied its reactivity and catalytic performance. Remarkable initial activities up to 283?000 h(-1) were achieved in the hydrogenation of ethyl hexanoate at only 12.5 ppm Ru loading. A wide range of aliphatic and aromatic esters can be converted with this catalyst to corresponding alcohols in near quantitative yields. The described synthetic protocol makes use of air-stable reagents available in multigram quantities, rendering the bis-NHC ligands an attractive alternative to the conventional phosphine-based systems. PMID:26052835

  7. Chromene chromium carbene complexes in the syntheses of naphthopyran and naphthopyrandione units present in photochromic materials and biologically active natural products.

    PubMed

    Rawat, Manish; Prutyanov, Victor; Wulff, William D

    2006-08-30

    The carbene complex 5-(2,2-dimethyl-2H-chromene)methoxylmethylene chromium pentacarbonyl will undergo a benzannulation reaction with phenylacetylene, 1-pentyne, 3-hexyne, and trimethylsilylacetylene to give 7-hydroxy-10-methoxy-3H-naphtho[2.1-b]pyrans as the primary product. These compounds are difficult to obtain pure due to their sensitivity to air. If the benzannulation reaction is performed in conjunction with protection of the phenol function at C-7, then good to excellent yields of 7-alkoxy-10-methoxy-3H-naphtho[2.1-b]pyrans are afforded. If the 7-hydroxy products are captured by triflic anhydride, then the resulting aryl triflate can be used to access 3H-naphtho[2.1-b]pyrans bearing C-7 carbon substituents. The 7-hydroxy products can be oxidized to 3H-naphtho[2,1-b]pyran-7,10-diones which are stable. The chromenyl carbene complex reacts with 1,6-bis(triisopropylsilyl)-1,3,5-hexatriyne to give a 2,3-dihydro-2,2-dimethylbenzo[de]chromene, a product type that has not been seen before in the reaction of Fischer carbene complexes with alkynes. A mechanism is proposed for this process that involves alpha,beta-hydride elimination from a chromacyclobutane intermediate. Chromenyl tungsten complexes react with alkynes to give products that result from cyclization without CO insertion. PMID:16925420

  8. Catalytic and Biocatalytic Iron Porphyrin Carbene Formation: Effects of Binding Mode, Carbene Substituent, Porphyrin Substituent, and Protein Axial Ligand.

    PubMed

    Khade, Rahul L; Zhang, Yong

    2015-06-24

    Iron porphyrin carbenes (IPCs) are important intermediates in various chemical reactions catalyzed by iron porphyrins and engineered heme proteins, as well as in the metabolism of various xenobiotics by cytochrome P450. However, there are no prior theoretical reports to help understand their formation mechanisms and identify key information governing the binding mode, formation feasibility, and stability/reactivity. A systematic quantum chemical study was performed to investigate the effects of carbene substituent, porphyrin substituent, and axial ligand on IPC formation pathways. Results not only are consistent with available experimental data but also provide a number of unprecedented insights into electronic, steric, and H-bonding effects of various structural factors on IPC formation mechanisms. These results shall facilitate research on IPC and related systems for sustainable chemical catalysis and biocatalysis. PMID:26067900

  9. The Depolymerization of Poly(Ethylene Terephthalate) (PET) Using N-Heterocyclic Carbenes from Ionic Liquids

    ERIC Educational Resources Information Center

    Kamber, Nahrain E.; Tsujii, Yasuhito; Keets, Kate; Waymouth, Robert M.; Pratt, Russell C.; Nyce, Gregory W.; Hedrick, James L.

    2010-01-01

    The depolymerization of the plastic polyethylene terephthalate (PET or PETE) is described in this laboratory procedure. The transesterification reaction used to depolymerize PET employs a highly efficient N-heterocyclic carbene catalyst derived from a commercially available imidazolium ionic liquid. N-heterocyclic carbenes are potent nucleophilic…

  10. Organometallic rhenium(iii) chalcogenide clusters: coordination of N-heterocyclic carbenes.

    PubMed

    Durham, Jessica L; Wilson, Wade B; Huh, Daniel N; McDonald, Robert; Szczepura, Lisa F

    2015-06-16

    The preparation of rhenium based octahedral clusters containing N-heterocyclic carbenes is described. These represent the first examples of [M6(?3-Q)8](n+) or [M6(?3-X)8](n+) clusters to contain a carbene ligand of any type (NHC, Fischer or Schrock). Surprisingly, the NHC ligands attenuate their luminescent properties. PMID:26041404

  11. Deprotonation of a Borohydride: Synthesis of a Carbene-Stabilized Boryl Anion**

    PubMed Central

    Ruiz, David A.; Ung, Gaël; Melaimi, Mohand

    2013-01-01

    An acidic hydride! Thanks to the presence of a ?-acceptor cyclic (alkyl)(amino)carbene (CAAC) and of two electron-withdrawing nitrile groups, a borohydride reacts with a base to give a carbene-stabilized boryl anion, which reacts with carbon and metal electrophiles at the boron center. PMID:23765789

  12. "Decarbonization" of an imino-N-heterocyclic carbene ligand via triple benzyl migration from hafnium.

    PubMed

    Prema, Dipesh; Mathota Arachchige, Yohan L N; Murray, Rex E; Slaughter, LeGrande M

    2015-04-21

    An imino-N-heterocyclic carbene underwent three sequential benzyl migrations upon reaction with tetrabenzylhafnium, resulting in complete removal of the carbene carbon from the ligand. The resulting eneamido-amidinato hafnium complex showed alkene polymerization activity comparable to that of a precatalyst containing the intact iminocarbene ligand. PMID:25790221

  13. Decarbonization of an imino N-heterocyclic carbene via triple benzyl migration from tetrabenzylhafnium

    Technology Transfer Automated Retrieval System (TEKTRAN)

    An imino N-heterocyclic carbene underwent three sequential benzyl migrations upon reaction with tetrabenzylhafnium, resulting in complete removal of the carbene carbon from the ligand. The resulting eneamido-amidinato hafnium complex showed alkene polymerization activity comparable to that of a prec...

  14. First Astronomical Detection of the Carbene Chain H2C6

    NASA Technical Reports Server (NTRS)

    Langer, W. D.; Velusamy, T.; Kuiper, T. B. H.; McCarthy, M. C.; Travers, M. J.; Kovacs, A.; Gottlieb, C. A.; Thaddeus, P.

    1996-01-01

    The cumulene carbenes are important components of hydrocarbon chemistry in low mass star forming cores. Here we report the first astronomical detection of the long chain cumulene carbene H(sub 2)C(sub 6), in the insterstellar cloud TMC1, from observations of two of its rotational transitions:...

  15. Synthesis, isolation and characterization of cationic gold(I) N-heterocyclic carbene (NHC) complexes.

    PubMed

    de Frémont, Pierre; Stevens, Edwin D; Fructos, Manuel R; Mar Díaz-Requejo, M; Pérez, Pedro J; Nolan, Steven P

    2006-05-21

    A number of cationic gold(I) complexes have been synthesized and found to be stabilized by the use of N-heterocyclic carbene ligands. These species are often employed as in situ-generated reactive intermediates in gold catalyzed organic transformations. An isolated, well-defined species was tested in gold-mediated carbene transfer reactions from ethyl diazoacetate. PMID:16767270

  16. Synthesis, Characterization, and Reactivity of a Uranium(VI) Carbene Imido Oxo Complex**

    PubMed Central

    Lu, Erli; Cooper, Oliver J; McMaster, Jonathan; Tuna, Floriana; McInnes, Eric J L; Lewis, William; Blake, Alexander J; Liddle, Stephen T

    2014-01-01

    We report the uranium(VI) carbene imido oxo complex [U(BIPMTMS)(NMes)(O)(DMAP)2] (5, BIPMTMS=C(PPh2NSiMe3)2; Mes=2,4,6-Me3C6H2; DMAP=4-(dimethylamino)pyridine) which exhibits the unprecedented arrangement of three formal multiply bonded ligands to one metal center where the coordinated heteroatoms derive from different element groups. This complex was prepared by incorporation of carbene, imido, and then oxo groups at the uranium center by salt elimination, protonolysis, and two-electron oxidation, respectively. The oxo and imido groups adopt axial positions in a T-shaped motif with respect to the carbene, which is consistent with an inverse trans-influence. Complex 5 reacts with tert-butylisocyanate at the imido rather than carbene group to afford the uranyl(VI) carbene complex [U(BIPMTMS)(O)2(DMAP)2] (6). PMID:24842784

  17. On the stability of perfluoroalkyl-substituted singlet carbenes: a coupled-cluster quantum chemical study.

    PubMed

    Rozhenko, Alexander B; Schoeller, Wolfgang W; Leszczynski, Jerzy

    2014-02-27

    A series of trifluoromethyl-substituted carbenes R-C(:)-CF3 (R = NMe2, OMe, F, PMe2, P(NMe2)2, P(N(Pr-i)2)2, SMe, Cl); (dimethylamino)(perfluoroalkyl)carbenes Me2N-C(:)-R (R = CF3, C2F5, n-C3F7, i-C3F7, and t-C4F9) and symmetrically substituted carbenes R-C(:)-R (R = NMe2, OMe, F, PMe2, SMe, Cl) have been investigated by means of quantum chemistry methods. Different levels of approximation were used, including the CCSD(T) approach also known in quantum chemistry as the "golden standard", in combination with three different basis sets (TZVP, cc-pVDZ, cc-pVTZ). Relative stabilities of carbenes have been estimated using the differences between the singlet and triplet ground state energies (?EST) and energies of the hydrogenation reaction for the singlet and triplet ground states of the carbenes. The latter seem to correlate better with stability of carbenes than the ?EST values. The (13)C NMR chemical shifts of the methylidene carbon indicate the more high-field chemical shift values in the known, isolable carbenes compared to the unstable ones. This is the first report on the expected chemical shifts in the highly unstable singlet carbenes. Using these criteria, some carbene structures from the studied series (as, for instance, Me2N-C(:)-CF3, Me2N-C(:)-C3F7-i) are proposed as good candidates for the experimental preparation. PMID:24471524

  18. New features of ROMP by heterogenization of molybdenum carbene complexes

    Microsoft Academic Search

    Peter Preishuber-Pflügl; Petra Buchacher; Elisabeth Eder; Regina M. Schitter; Franz Stelzer

    1998-01-01

    An inorganic carrier based on alumina covered with methylaluminoxane (MAO) which had been crosslinked by various diols was used to immobilize molybdenum carbene complexes of the type Mo(CH-t-Bu)(NAr)(OC(CH3)2CF3)2(1) and Mo(CH-t-Bu)(NAr)(OTf)2(dme) (2) (Ar?2,6-C6H3-i-Pr2). Employment of fluorinated diols heavily increased the activity in ring-opening metathesis polymerization (ROMP) of different substituted norbornenes, 2-azanorbornene, cyclooctene, cyclooctadiene and metathesis reaction of acyclic alkenes. Investigations were

  19. Methanol dehydrogenation by iridium N-heterocyclic carbene complexes.

    PubMed

    Campos, Jesús; Sharninghausen, Liam S; Manas, Michael G; Crabtree, Robert H

    2015-06-01

    A series of homogeneous iridium bis(N-heterocyclic carbene) catalysts are active for three transformations involving dehydrogenative methanol activation: acceptorless dehydrogenation, transfer hydrogenation, and amine monoalkylation. The acceptorless dehydrogenation reaction requires base, yielding formate and carbonate, as well as 2-3 equivalents of H2. Of the few homogeneous systems known for this reaction, our catalysts tolerate air and employ simple ligands. Transfer hydrogenation of ketones and imines from methanol is also possible. Finally, N-monomethylation of anilines occurs through a "borrowing hydrogen" reaction. Notably, this reaction is highly selective for the monomethylated product. PMID:25615426

  20. An abnormal N-heterocyclic carbene-carbon dioxide adduct from imidazolium acetate ionic liquids: the importance of basicity.

    PubMed

    Kelemen, Zsolt; Péter-Szabó, Barbara; Székely, Edit; Hollóczki, Oldamur; Firaha, Dzmitry S; Kirchner, Barbara; Nagy, József; Nyulászi, László

    2014-09-26

    In the reaction of 1-ethyl-3-methylimidazolium acetate [C2C1Im][OAc] ionic liquid with carbon dioxide at 125?°C and 10?MPa, not only the known N-heterocyclic carbene (NHC)-CO2 adduct I, but also isomeric aNHC-CO2 adducts II and III were obtained. The abnormal NHC-CO2 adducts are stabilized by the presence of the polarizing basic acetate anion, according to static DFT calculations and ab initio molecular dynamics studies. A further possible reaction pathway is facilitated by the high basicity of the system, deprotonating the initially formed NHC-CO2 adduct I, which can then be converted in the presence of the excess of CO2 to the more stable 2-deprotonated anionic abnormal NHC-CO2 adduct via the anionic imidazolium-2,4-dicarboxylate according to DFT calculations on model compounds. This suggests a generalizable pathway to abnormal NHC complex formation. PMID:25137312

  1. Copper-Carbene Intermediates in the Copper-Catalyzed Functionalization of O?H Bonds.

    PubMed

    Pereira, Ana; Champouret, Yohan; Martín, Carmen; Álvarez, Eleuterio; Etienne, Michel; Belderraín, Tomás R; Pérez, Pedro J

    2015-06-26

    Copper-carbene [Tp(x) Cu?C(Ph)(CO2 Et)] and copper-diazo adducts [Tp(x) Cu{?(1) -N2 C(Ph)(CO2 Et)}] have been detected and characterized in the context of the catalytic functionalization of O?H bonds through carbene insertion by using N2 ?C(Ph)(CO2 Et) as the carbene source. These are the first examples of these type of complexes in which the copper center bears a tridentate ligand and displays a tetrahedral geometry. The relevance of these complexes in the catalytic cycle has been assessed by NMR spectroscopy, and kinetic studies have demonstrated that the N-bound diazo adduct is a dormant species and is not en route to the formation of the copper-carbene intermediate. PMID:26014686

  2. Activation of molecular hydrogen by a singlet carbene through quantum mechanical tunneling.

    PubMed

    Henkel, Stefan; Sander, Wolfram

    2015-04-01

    Carbenes are among the few metal-free molecules that are able to activate molecular hydrogen. Whereas triplet carbenes have been shown to insert into H2 through a two-step mechanism that at low temperature is assisted by quantum mechanical tunneling (QMT), singlet carbenes insert in concerted reactions with considerable activation barriers, and are thus unreactive towards H2 at cryogenic temperatures. Here we show that 1-azulenylcarbene with a singlet ground state readily inserts into H2 , and that QMT governs the insertion into both H2 and D2 . This is the first example that shows that QMT can also be important for singlet carbenes inserting into dihydrogen. PMID:25690272

  3. PEGylated N-Heterocyclic Carbene Anchors Designed To Stabilize Gold Nanoparticles in Biologically Relevant Media.

    PubMed

    MacLeod, Michelle J; Johnson, Jeremiah A

    2015-07-01

    N-Heterocyclic carbenes (NHCs) have emerged as versatile ligands for surface functionalization. Their ease of synthesis and ability to form strong bonds with a range of substrates provide a unique complement to traditional surface modification methods. Gold nanoparticles (NPs) are a particularly useful class of materials whose applications intimately depend on surface functionalization. Here we report the development of PEGylated-NHC ligands for Au-NP surfaces and the first example of NHC-functionalized NPs that are compatible with biologically relevant conditions. Our PEGylated-NHC-Au-NPs are stable toward aggregation in aqueous solutions in the pH range of 3-14, in <250 mM electrolyte solutions, at high and low temperatures (95 and -78 °C), in cell culture media, and in aqueous H2O2 solutions. This work demonstrates for the first time that NHCs can serve as anchors for water-soluble Au-NPs and opens the door to potential biomedical applications of NHC surface anchors. PMID:26081724

  4. Air-Persistent Monomeric (Amino)(carboxy) Radicals Derived from Cyclic (Alkyl)(Amino) Carbenes.

    PubMed

    Mahoney, Janell K; Martin, David; Thomas, Fabrice; Moore, Curtis E; Rheingold, Arnold L; Bertrand, Guy

    2015-06-17

    A series of monomeric (amino)(carboxy) radicals featuring carbonyl substituents with increasing electron-withdrawing properties (3a, phenyl; 3b, 3,5-bis(trifluoromethyl)phenyl; 3c, perfluorophenyl; 3d, heptafluoropropyl; 3e, 2H-pyrroliumyl) were synthesized in two or three steps from stable cyclic (alky)(amino)carbenes (CAACs). Although (amino)(carboxy) radicals had been previously considered as highly air-sensitive, some of these compounds feature half-lives of hours (3d), and even days (3c and 3e) in well-aerated solutions. DFT calculations show that (amino)(carboxy) radicals evolve from C-centered radical to ambidentate C,O-radicals when increasing the electron-withdrawing properties of the carbonyl substituent. This is paralleled with a destabilization of the peroxide resulting from the addition of dioxygen to the radical. This latter reaction is even predicted to be endothermic for substituents with Hammett constant ?p > 0.2. PMID:26011769

  5. N-heterocyclic carbene (NHC) complexes of group 4 transition metals.

    PubMed

    Zhang, Dao; Zi, Guofu

    2015-04-01

    Since the discovery of a stable N-heterocyclic carbene (NHC), the use of NHCs in chemistry has developed rapidly over the past two decades. These interesting compounds are predominantly employed in organometallic chemistry as ligands for various metal centers, and as organocatalysts for a variety of transformations. In particular, the NHC transition metal complexes have received widespread attention, and significant progress has been made in the development of group 4 NHC-complexes in the last few years. These group 4 NHC-complexes are of interest because of their unique structural properties, and their potential application in organic transformations and catalysis. This review covers the superior design strategies for NHC ligands to stabilize early transition metals and well-defined group 4 metal complexes with mono- and multi-dentate NHC ligands. In this context, four types of NHC-complexes, i.e., carbon-functionalized NHCs, nitrogen-functionalized NHCs, oxygen-functionalized NHCs and nitrogen/oxygen-functionalized unsymmetric NHCs, are described. In addition, the use of group 4 NHC-complexes as catalysts in olefin (co)polymerization, ring-opening polymerization of rac-lactide, copolymerization of epoxides and CO2, as well as hydroamination/cyclization of aminoalkenes, is presented. Furthermore, limitations and challenges are discussed. PMID:25608933

  6. Design and Synthesis of C2-Symmetric N-Heterocyclic Carbene Precursors and Metal Carbenoids

    PubMed Central

    Albright, Abigail; Eddings, Daniel; Black, Regina; Welch, Christopher J.; Gerasimchuk, Nikolay N.; Gawley, Robert E.

    2011-01-01

    Chiral, C2-symmetric imidazolium and imidazolinium ions, as well as the corresponding copper or silver bound carbenoids, have been prepared. Structural study of these compounds by X-ray crystallography reveals a chiral pocket that surrounds the putative carbene site or the metal-carbene bond, at carbon 2, in three of the four ligands prepared. Preliminary investigation into the application of these complexes has shown one of them to be highly enantioselective in the hydrosilylation of acetophenone. PMID:21823580

  7. Quantitative description of structural effects on the stability of gold(I) carbenes.

    PubMed

    Ringger, David H; Kobylianskii, Ilia J; Serra, Daniel; Chen, Peter

    2014-10-27

    The gas-phase bond-dissociation energies of a SO2 -imidazolylidene leaving group of three gold(I) benzyl imidazolium sulfone complexes are reported (E0 =46.6±1.7, 49.6±1.7, and 48.9±2.1?kcal?mol(-1) ). Although these energies are similar to each other, they are reproducibly distinguishable. The energy-resolved collision-induced dissociation experiments of the three [L]-gold(I) (L=ligand) carbene precursor complexes were performed by using a modified tandem mass spectrometer. The measurements quantitatively describe the structural and electronic effects a p-methoxy substituent on the benzyl fragment, and trans [NHC] and [P] gold ligands, have towards gold carbene formation. Evidence for the formation of the electrophilic gold carbene in solution was obtained through the stoichiometric and catalytic cyclopropanation of olefins under thermal conditions. The observed cyclopropane yields are dependent on the rate of gold carbene formation, which in turn is influenced by the ligand and substituent. The donation of electron density to the carbene carbon by the p-methoxy benzyl substituent and [NHC] ligand stabilizes the gold carbene intermediate and lowers the dissociation barrier. Through the careful comparison of gas-phase and solution chemistry, the results suggest that even gas-phase leaving-group bond-dissociation energy differences of 2-3?kcal?mol(-1) enormously affect the rate of gold carbene formation in solution, especially when there are competing reactions. The thermal decay of the gold carbene precursor complex was observed to follow first-order kinetics, whereas cyclopropanation was found to follow pseudo-first-order kinetics. Density-functional-theory calculations at the M06-L and BP86-D3 levels of theory were used to confirm the observed gas-phase reactivity and model the measured bond-dissociation energies. PMID:25236486

  8. Synthesis and solvent dependent reactivity of chelating bis-N-heterocyclic carbene complexes of Fe(II) hydrides.

    PubMed

    Zlatogorsky, Sergey; Ingleson, Michael J

    2012-03-01

    The synthesis and isolation of low coordinate methylenebis-(N-DIPP-imidazole-2-ylidene)iron((II))hydrides, (((DIPP)C)(2)CH(2))FeH(2-y)I(y) ((DIPP = 2,6-di-isopropylphenyl, y = 1 or 0), was complicated by competitive reactions with solvent, rapid reductive elimination of H(2) and/or dissociation of the bis-N-heterocyclic carbene ligand. Addition of KH to (((DIPP)C)(2)CH(2))FeI(2) in THF/haloalkane mixtures enabled a short lived mono-hydride to be trapped by reaction with CH(2)Cl(2) or cyclo-heptylbromide to form (((DIPP)C)(2)CH(2))FeI(X) (X = Cl or Br, respectively). Toluene coordination stabilises iron-mono hydride complexes as (((DIPP)C)(2)CH(2))Fe(II)H{?(6)-(toluene)} species, which can be isolated in low yield from combination of borohydride salts and (((DIPP)C)(2)CH(2))FeI(2) in toluene, including an imidazole C4 deprotonated carbene-borane, methylene(N-DIPP-imidazole-2-ylidene)(N-DIPP-4-triethyl-borane-imidazole-2-ylidene)](hydrido)(?(6)-toluene)iron. In the absence of toluene, or at short reaction times compounds with empirical formula (((DIPP)C)(2)CH(2))Fe(H)(HB(R)(3))·LiI (R = Et or sec-Bu) that function as a masked Fe((II))-dihydride are isolated. Whilst (((DIPP)C)(2)CH(2))Fe(H)(HB(R)(3))·LiI was stable for days in Et(2)O, more polar solvents (MeCN, THF) led to formation of the carbene borane adducts (((DIPP)C)(2)CH(2))(BR(3))(2). The addition of CO or cyclo-heptylbromide to (((DIPP)C)(2)CH(2))Fe(H)(HB(R)(3))·LiI formed (((DIPP)C)(2)CH(2))Fe(CO)(3) and (((DIPP)C)(2)CH(2))FeBr(2), respectively with BR(3) evolved from both reactions as a by-product. PMID:22234675

  9. Alkyne hydroarylation with Au N-heterocyclic carbene catalysts

    PubMed Central

    Tubaro, Cristina; Baron, Marco; Basato, Marino

    2013-01-01

    Summary Mono- and dinuclear gold complexes with N-heterocyclic carbene (NHC) ligands have been employed as catalysts in the intermolecular hydroarylation of alkynes with simple unfunctionalised arenes. Both mono- and dinuclear gold(III) complexes were able to catalyze the reaction; however, the best results were obtained with the mononuclear gold(I) complex IPrAuCl. This complex, activated with one equivalent of silver tetrafluoroborate, exhibited under acidic conditions at room temperature much higher catalytic activity and selectivity compared to more commonly employed palladium(II) catalysts. Moreover, the complex was active, albeit to a minor extent, even under neutral conditions, and exhibited lower activity but higher selectivity compared to the previously published complex AuCl(PPh3). Preliminary results on intramolecular hydroarylations using this catalytic system indicate, however, that alkyne hydration by traces of water may become a serious competing reaction. PMID:23400639

  10. N-Heterocyclic Carbene Complexes in Reactions Involving Carbon Monoxide

    NASA Astrophysics Data System (ADS)

    Jeletic, Matthew; Veige, Adam

    This chapter focuses on carbon monoxide as a reagent in M-NHC catalysed reactions. The most important and popular of these reactions is hydroformylation. Unfortunately, uncertainty exists as to the identity of the active catalyst and whether the NHC is bound to the catalyst in a number of the reported reactions. Mixed bidentate NHC complexes and cobalt-based complexes provide for better stability of the catalyst. Catalysts used for hydroaminomethylation and carbonylation reactions show promise to rival traditional phosphine-based catalysts. Reports of decarbonylation are scarce, but the potential strength of the M-NHC bond is conducive to the harsh conditions required. This report will highlight, where appropriate, the potential benefits of exchanging traditional phosphorous ligands with N-heterocyclic carbenes as well as cases where the role of the NHC might need re-evaluation. A review by the author on this topic has recently appeared [1].

  11. Stabilization of Fully Reduced Iron–Sulfur Clusters by Carbene Ligation: The [FenSn]0 Oxidation Levels (n = 4, 8)

    PubMed Central

    Deng, Liang

    2008-01-01

    The all-ferrous [Fe4S4]0 state has been demonstrated in the fully reduced Fe protein of the Azotobacter vinelandii nitrogenase complex. We seek synthetic analogues of this state more tractable than the recently prepared but highly unstable cluster [Fe4S4(CN)4]4? (Scott, Berlinguette, Holm, and Zhou, Proc. Natl. Acad. Sci. U.S.A. 2005, 102, 9741). The N-heterocyclic carbene 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (Pri2NHCMe2) has been found to stabilize the fully reduced clusters [Fe8S8(Pri2NHCMe2)6] (4) and [Fe4S4(Pri2NHCMe2)4] (5), which are prepared by cluster assembly or phosphine substitution of FenSn (n = 8, 16) clusters. Cluster 4 is also obtained by reaction of the carbene with all-ferrous [Fe7S6(PEt3)5Cl2] (3) and cluster 5 by carbene cleavage of 4. Detailed structures of 3 (monocapped prismatic), 4, and 5 are described; the latter two are the first iron–sulfur clusters with Fe–C? bonds. Cluster 4 possesses the [Fe8(?3-S)6(?4-S)2] edge-bridged double cubane structure and 5 the cubane-type [Fe4(?3-S)4] stereochemistry. The all-ferrous formulations of the clusters are confirmed by X-ray structure parameters and 57Fe isomer shifts. Both clusters are stable under conventional aprotic anaerobic conditions, enabling further study of reactivity. The collective properties of 5 indicate that it is a meaningful synthetic analogue of the core of the fully reduced protein-bound cluster. PMID:18593124

  12. Highly efficient [2,3]-sigmatropic rearrangement of sulfur ylide derived from Rh(II) carbene and sulfides in water

    E-print Network

    Wang, Jianbo

    Engineering of Ministry of Education, College of Chemistry Peking University, Beijing, 100871, China. E between a carbene (or carbenoid) and a sulfide. Although suitable for ylide formation, carbenes generated­C bond formation (Scheme 1).4 Therefore, many metal catalysts, such as Rh2(OAc)4, Cu(acac)2, [RuII (TTP

  13. The influence of anionic ligands on stereoisomerism of Ru carbenes and their importance to efficiency and selectivity of catalytic olefin metathesis reactions.

    PubMed

    Torker, Sebastian; Khan, R Kashif M; Hoveyda, Amir H

    2014-03-01

    Investigations detailed herein provide insight regarding the mechanism of stereochemical inversion of stereogenic-at-Ru carbene complexes through a nonolefin metathesis-based polytopal rearrangement pathway. Computational analyses (DFT) reveal that there are two key factors that generate sufficient energy barriers that are responsible for the possibility of isolation and characterization of high-energy, but kinetically stable, intermediates: (1) donor-donor interactions that involve the anionic ligands and the strongly electron donating carbene groups and (2) dipolar effects arising from the syn relationship between the anionic groups (iodide and phenoxide). We demonstrate that a Brønsted acid lowers barriers to facilitate isomerization, and that the positive influence of a proton source is the result of its ability to diminish the repulsive electronic interactions originating from the anionic ligands. The implications of the present studies regarding a more sophisticated knowledge of the role of anionic units on the efficiency of Ru-catalyzed olefin metathesis reactions are discussed. The electronic basis for the increased facility with which allylic alcohols participate in olefin metathesis processes will be presented as well. Finally, we illustrate how a better understanding of the role of anionic ligands has served as the basis for successful design of Ru-based Z-selective catalysts for alkene metathesis. PMID:24533571

  14. Correlation between thermal and mass spectral techniques for the characterization of allenylidene and carbene complexes

    NASA Astrophysics Data System (ADS)

    Mohamed, Gehad G.; Szesni, Normen; Fischer, Helmut

    2008-11-01

    The fragmentation pathways of allenylidene and carbene complexes have been studied using FAB mass spectrometry in comparison with thermal analyses (TGA, DrTG and DTA). Both the decomposition modes are investigated and the possible fragmentation pathways are suggested. The use of mass and thermal analyses (TGA and DTA) in the analyses of allenylidene and carbene complexes allowed the characterization of the fragmentation pathways in MS. The major pathway includes successive loss of carbon monoxide followed by fragmentation of the organic part of the allenylidene or carbene molecules. This is also confirmed by thermogravimetric analysis (TGA) where the first step involves the loss of carbon monoxide followed by the organic ligand. The nature of each step; exothermic or endothermic, is also studied using DTA technique. The kinetic parameters of the thermal decomposition are also studied using the Coates-Redfern method.

  15. A Continuum of Progress: Applications of N-Hetereocyclic Carbene Catalysis in Total Synthesis

    PubMed Central

    Izquierdo, Javier; Hutson, Gerri E.; Cohen, Daniel T.; Scheidt, Karl A.

    2013-01-01

    N-Heterocyclic carbene (NHC) catalyzed transformations have emerged as powerful tactics for the construction of complex molecules. Since Stetter’s report in 1975 of the total synthesis of cis-jasmon and dihydrojasmon by using carbene catalysis, the use of NHCs in total synthesis has grown rapidly, particularly over the last decade. This renaissance is undoubtedly due to the recent developments in NHC-catalyzed reactions, including new benzoin, Stetter, homoenolate, and aroylation processes. These transformations employ typical as well as Umpolung types of bond disconnections and have served as the key step in several new total syntheses. This Minireview highlights these reports and captures the excitement and emerging synthetic utility of carbene catalysis in total synthesis. PMID:23074146

  16. An N-heterocyclic carbene phenanthroline ligand: synthesis, multi-metal coordination and spectroscopic studies.

    PubMed

    Webster, Alyssa A; Prasad, Shyamal K K; Hodgkiss, Justin M; Hoberg, John O

    2015-02-28

    Dimetal complexes of a new N-heterocyclic carbene/phenanthroline ligand have been synthesized. Coordination of both ruthenium and rhenium to the phenanthroline moiety in combination with platinum at the carbene moiety are reported. Steady-state and time-resolved optical absorption and photoluminescence spectra were obtained for the complexes. These results illustrate significant changes occur with the incorporation of the second metal, and that the specific metal bound to the phenanthroline moiety is important to the photophysical characteristics of this system. PMID:25604044

  17. Highly selective palladium–benzothiazole carbene-catalyzed allylation of active methylene compounds under neutral conditions

    PubMed Central

    Cotugno, Pietro; Zambonin, Carlo Giorgio; Ciminale, Francesco

    2015-01-01

    Summary The Pd–benzothiazol-2-ylidene complex I was found to be a chemoselective catalyst for the Tsuji–Trost allylation of active methylene compounds carried out under neutral conditions and using carbonates as allylating agents. The proposed protocol consists in a simplified procedure adopting an in situ prepared catalyst from Pd2dba3 and 3-methylbenzothiazolium salt V as precursors. A comparison of the performance of benzothiazole carbene with phosphanes and an analogous imidazolium carbene ligand is also proposed. PMID:26199653

  18. Olefin Metathesis With Ruthenium-Arene Catalysts Bearing N-Heterocyclic Carbene Ligands

    NASA Astrophysics Data System (ADS)

    Delaude, Lionel; Demonceau, Albert

    In this chapter, we summarize the main results of our investigations on the ring-opening metathesis polymerization (ROMP) of cyclooctene catalyzed by various ruthenium (Ru)-arene complexes bearing imidazolin-2-ylidene, imidazolidin- 2-ylidene, or triazolin-5-ylidene ligands. Three major findings emerged from this study. First, we underscored the intervention of a photochemical activation step due to visible light illumination. Second, we established that the presence of an endocyclic double bond in the carbene ligand central heterocycle was not crucial to achieve high catalytic efficiencies. Third, we demonstrated that ortho-metallation of the N-heterocyclic carbene (NHC) ligand by the Ru center led to inactive catalysts.

  19. {alpha},{beta}-Unsaturated Fischer carbene complexes as chemical multitalents

    SciTech Connect

    Meijere, A. de [Institut fuer Organische Chemie der George-August-Universitaet Goettingen (Germany)

    1995-12-31

    The well established reaction of {alpha},{beta}-unsaturated Fischer carbenechromium complexes 6(R{sup 1} = H) with alkynes normally proceeds with carbonyl insertion to yield 4-alkoxyphenols 9. Led by the incidental formation of a cyclopentadiene 3 from certain {beta}-aminosubstituted complexes 6(X = NR{sub 2}{sup 3}, R{sup 1} = cPr) the authors have studied the influences of the nature of substituents (R{sup 1}, X on 6; R{sub L}, R{sub S} in the alkyne; R{sup 3} in the amino group), solvents, and temperature on the outcome of the reaction. Imino substitution on complexes 6 leads to 2H-pyrroles 1, a free primary amino group (X = NH{sub 2}) to pyridines 5, and bulky substituents R{sup 1} to cyclopenta[b]pyrans 8 with double insertion of an alkyne. Eventually, appropriate conditions have been developed which permit to selectively prepare either 3-alkoxy-5-(dialkylamino)cyclopentadienes 3 (as synthetic equivalents of cyclopentenones 4), 5-(dialkylaminomethylene)cyclopent-2-enones 7, 3-alkoxy-2-(1{prime}-morpholino-1{prime}-alkenyl)cyclopent-2-enones 10, and 2-acyl-3-(dialkylamino)cyclopent-2-enones 11 from easily accessible carbene complexes 6 (X = NR{sub 2}{sup 3}) in high yields. Mechanistic aspects and implications of these novel transformations will be discussed.

  20. Homobimetallic Ruthenium-N-Heterocyclic Carbene Complexes For Olefin Metathesis

    NASA Astrophysics Data System (ADS)

    Sauvage, Xavier; Demonceau, Albert; Delaude, Lionel

    In this chapter, the synthesis and catalytic activity towards olefin metathesis of homobimetallic ruthenium (Ru)-alkylidene, -cyclodiene or -arene complexes bearing phosphine or N-heterocyclic carbene (NHC) ligands are reviewed. Emphasis is placed on the last category of bimetallic compounds. Three representatives of this new type of molecular scaffold were investigated. Thus, [(p-cymene)Ru(m-Cl)3RuCl (h2-C2H4)(L)] complexes with L = PCy3 (15a), IMes (16a), or IMesCl2 (16b) were prepared. They served as catalyst precursors for cross-metathesis (CM) of various styrene derivatives. These experiments revealed the outstanding aptitude of complex 16a (and to a lesser extent of 16b) to catalyze olefin metathesis reactions. Contrary to monometallic Ru-arene complexes of the [RuCl2(p-cymene)(L)] type, the new homobimetallic species did not require the addition of a diazo compound nor visible light illumination to initiate the ring-opening metathesis of norbornene or cyclooctene. When diethyl 2,2-diallylmalonate and N,N-diallyltosylamide were exposed to 16a,b, a mixture of cycloisomerization and ring-closing metathesis (RCM) products was obtained in a nonselective way. Addition of phenylacetylene enhanced the metathetical activity while completely repressing the cycloisomerization process.

  1. Carbene Singlets, Triplets, and the Physics that describes them Louis Smith

    E-print Network

    Rosner, Jonathan L.

    for Quantum Mechanics II Contents 1. Introduction 2. Organic Chemistry a. Skeleton Structures and extensions thereof b. Molecular Orbitals and molecular interactions c. Carbenes in terms of this formalism 3 electronic structure b. Improvements on this theory c. Relationship to Organic Chemistry d. Difficulties

  2. Theoretical Study of Dithioformic Acid, Dithiohydroxy Carbene and Their Radical Cations: Unimolecular and Assisted Rearrangements

    E-print Network

    Nguyen, Minh Tho

    , dithiohydroxy carbene, in both neutral and ionized states have been investigated using ab initio molecular derived from numerous ab initio molecular orbital calculations.6-15 Thus, its structure, charge in which both oxygens of the carboxyl group are formally replaced by sulfur atoms. While the properties

  3. 2009 Macmillan Publishers Limited. All rights reserved. A bonding model for gold(I) carbene complexes

    E-print Network

    Goddard III, William A.

    © 2009 Macmillan Publishers Limited. All rights reserved. A bonding model for gold(I) carbene-stabilized cationic species, the nature of bonding in these intermediates remains unclear. Herein, we propose that the carbon­gold bond in these intermediates comprises varying degrees of both s- and p-bonding; however

  4. Heterobimetallic complexes with redox-active mesoionic carbenes as metalloligands: electrochemical properties, electronic structures and catalysis.

    PubMed

    Hettmanczyk, Lara; Manck, Sinja; Hoyer, Carolin; Hohloch, Stephan; Sarkar, Biprajit

    2015-06-23

    A mesoionic carbene with a ferrocene backbone is used as a metalloligand to generate the first example of their Fe-Au heterobimetallic complexes. The details of geometric and electronic structures in different redox states and preliminary catalytic results are presented. PMID:26063482

  5. Photochemistry of Metalloporphyrin Carbene Christopher J. Ziegler and Kenneth S. Suslick*

    E-print Network

    Suslick, Kenneth S.

    Photochemistry of Metalloporphyrin Carbene Complexes Christopher J. Ziegler and Kenneth S. SuslickVed December 6, 1995 The photochemistry of metalloporphyrins and other tetrapy- rrolic systems continues and a variety of metals, including chromium, manganese, and iron.3 The photochemistry of metalloporphyrins

  6. Homogeneous, anaerobic (N-heterocyclic carbene)-Pd or -Ni catalyzed oxidation of secondary alcohols at mild temperatures.

    PubMed

    Berini, Christophe; Brayton, Daniel F; Mocka, Corey; Navarro, Oscar

    2009-09-17

    The use of aryl chlorides as oxidants for the selective oxidation of a variety of secondary alcohols in anaerobic conditions with (NHC)-Pd and -Ni systems (NHC = N-heterocyclic carbene) at very mild temperatures is presented. PMID:19702279

  7. Synthesis and reactivity of metal carbene complexes with heterobiaryl spacer substituents.

    PubMed

    Lotz, Simon; Crause, Chantelle; Olivier, Andrew J; Liles, David C; Görls, Helmar; Landman, Marilé; Bezuidenhout, Daniela I

    2009-01-28

    Mono- and binuclear Fischer carbene complexes, [M(CO)5{C(OR)Ar-ArX}], X = H, {C(OR)M'(CO)5}; M, M' = W or Cr; R = Me, Et or (CH2)4OMe; Ar = thiophene, N-methylpyrrole or furan units 1-20, were synthesized. For this purpose, mono-, bi- or stepwise lithiated bithiophene, N,N'-dimethylbipyrrole, thienylfuran and N-methyl(thienyl)pyrrole were reacted with chromium and tungsten hexacarbonyl precursors. Dilithiation in the 2- and 9-positions of N-methyl(thienyl)pyrrole could not be achieved. Alkylation of acyl metallates with triethyloxonium tetrafluoroborate or methyl trifluoromethanesulfonate in THF afforded not only the expected carbene complexes with ethoxy or methoxy substituents, but in the case of bithiophene with methyl trifluoromethanesulfonate, carbene complexes with alkoxy substituents incorporating a ring-opened tetrahydrofuran moiety. X-Ray crystallographic structure determinations were performed on [W(CO)5{C(OMe)(thienylfuran)}] (14), [W(CO)5{C(OMe)(N-methylthienylpyrrole)}] (20) and [{W(CO)5}2{mu-C(OEt)(N,N'-dimethylbipyrrolylC(OEt)}] (12) to assess the role of the heterobiaryl substituent on the structural features of the carbene ligand in the complexes. Complexes [{Cr(CO)5}2{mu-C(OMe)bithienylC(OEt)}] (3), [(CO)5Cr{mu-C(OMe)bithienylC(OMe)}W(CO)5] (5) and [{Cr(CO)5}2 {mu-C(OMe)thienylfuranC-(OMe)}] (15) were reacted with 3-hexyne to study their behaviour in benzannulation reactions. The major products generated by the biscarbene complexes were regio-selectively determined by the nature of the metal site and that of the heteroatom in the arene rings. The monocarbene complexes [Cr(CO)5{C(OMe)thienylfuran] (13) and [Cr(CO)5{C(OEt)(N-methylthienylpyrrole)}] (19) were refluxed in THF for 2 hours in the presence of [Pd(PPh4)4] to afforded the carbene-carbene coupled olefinic products and small amounts of the corresponding 2-ethyl(biheteroaryl)acetate. By contrast, the biscarbene complex of thienylfuran (15), afforded only the 2,9-diester of thienylfuran. PMID:19378563

  8. A Dual Lewis Base Activation Strategy for Enantioselective Carbene-Catalyzed Annulations

    PubMed Central

    Izquierdo, Javier; Orue, Ane; Scheidt, Karl A.

    2013-01-01

    A dual activation strategy integrating NHC catalysis and a second Lewis base has been developed. NHC-bound homoenolate equivalents derived from ?,?-unsaturated aldehydes combine with transient reactive o-quinione methides in an enatioselective formal [4+3] fashion to access 2-benzoxopinones. The overall approach provides a general blueprint for the integration of carbene catalysis with additional Lewis base activations modes. PMID:23829462

  9. Efficient electronic communication of two ruthenium centers through a rigid ditopic N-heterocyclic carbene linker.

    PubMed

    Nussbaum, Michael; Schuster, Oliver; Albrecht, Martin

    2013-12-16

    A ditopic benzobis(carbene) ligand precursor was prepared that contained a chelating pyridyl moiety to ensure co-planarity of the carbene ligand and the coordination plane of a bound octahedral metal center. Bimetallic ruthenium complexes comprising this ditopic ligand [L4Ru-C,N-bbi-C,N-RuL4] were obtained by a transmetalation methodology (C,N-bbi-C,N=benzobis(N-pyridyl-N'-methyl-imidazolylidene). The two metal centers are electronically decoupled when the ruthenium is in a pseudotetrahedral geometry imparted by a cymene spectator ligand (L4=[(cym)Cl]). Ligand exchange of the Cl(-)/cymene ligands for two bipyridine or four MeCN ligands induced a change of the coordination geometry to octahedral. As a consequence, the ruthenium centers, separated through space by more than 10 Å, become electronically coupled, which is evidenced by two distinctly different metal-centered oxidation processes that are separated by 134 mV (L4=[(bpy)2]; bpy=2,2'-bipyridine) and 244 mV (L4=[(MeCN)4]), respectively. Hush analysis of the intervalence charge-transfer bands in the mixed-valent species indicates substantial valence delocalization in both complexes (delocalization parameter ?=0.41 and 0.37 in the bpy and MeCN complexes, respectively). Spectroelectrochemical measurements further indicated that the mixed-valent Ru(II)/Ru(III) species and the fully oxidized Ru(III)/Ru(III) complexes gradually decompose when bound to MeCN ligands, whereas the bpy spectators significantly enhance the stability. These results demonstrate the efficiency of carbenes and, in particular, of the bbi ligand scaffold for mediating electron transfer and for the fabrication of molecular redox switches. Moreover, the relevance of spectator ligands is emphasized for tailoring the degree of electronic communication through the benzobis(carbene) linker. PMID:24218243

  10. Pd-catalyzed cross-coupling of terminal alkynes with ene-yne-ketones: access to conjugated enynes via metal carbene migratory insertion.

    PubMed

    Xia, Ying; Liu, Zhen; Ge, Rui; Xiao, Qing; Zhang, Yan; Wang, Jianbo

    2015-06-30

    A novel strategy for alkyne-alkyne cross-coupling has been developed under the palladium catalysis. In this reaction, ene-yne-ketones are employed as carbene precursors, which couple with terminal alkynes through the metal carbene migratory insertion process. Furan-substituted enynes are obtained in good yields and in a stereoselective manner. PMID:26077197

  11. Palladium-catalyzed direct C2-arylation of an N-heterocyclic carbene: an atom-economic route to mesoionic carbene ligands.

    PubMed

    Ghadwal, Rajendra S; Reichmann, Sven O; Herbst-Irmer, Regine

    2015-03-01

    Blocking the C2 position of an imidazole-derived classical N-heterocyclic carbene (NHC) with an aryl group is an essential strategy to establish a route to mesoionic carbenes (MICs), which coordinate to the metal via the C4 (or C5) carbon atom. An efficient catalytic route to MIC precursors by direct arylation of an NHC is reported. Treatment of 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) with an aryl iodide (RC6H4I) in the presence of 0.5?mol?% of [Pd2(dba)3] (dba = dibenzylideneacetone) precatalyst affords the C2-arylated imidazolium salts {IPr(C6H4R)}I (R = H, 4-Me, 2-Me, 4-OMe, 4-COOMe) in excellent (up to 92%) yields. Treatment of {IPr(C6H5)}I with CuI and KN(SiMe3)2 exclusively affords the MIC-copper complex [(IPrPh)CuI]. PMID:25639790

  12. Splitting molecular oxygen en route to a stable molecule containing diphosphorus tetroxide.

    PubMed

    Wang, Yuzhong; Xie, Yaoming; Wei, Pingrong; Schaefer, Henry F; Schleyer, Paul von R; Robinson, Gregory H

    2013-12-26

    In contrast to stable phosphorus oxides such as P4O6 and P4O10 that possess iconic adamantane-like cage structures, highly reactive phosphorus oxides such as PO, PO2, and P2Ox (x = 1-5) only have been studied in the gas phase or by matrix isolation techniques. Elusive diphosphorus tetroxide, the long sought phosphorus analogue of N2O4, is particularly noteworthy. Computations predict that the oxo-bridged O2POPO form of P2O4 is energetically more favored than the P-P bonded O2P-PO2 isomer. Herein, we report the experimental realization of diphosphorus tetroxide-in its energetically disfavored O2P-PO2 form-via carbene-stabilization. The synthesis of the title compound involves the splitting of molecular oxygen by carbene-stabilized diphosphorus. PMID:24299493

  13. Synthesis and biological assays on cancer cells of dinuclear gold complexes with novel functionalised di(N-heterocyclic carbene) ligands.

    PubMed

    Baron, Marco; Bellemin-Laponnaz, Stéphane; Tubaro, Cristina; Basato, Marino; Bogialli, Sara; Dolmella, Alessandro

    2014-12-01

    New dinuclear di(N-heterocyclic carbene) silver(I), gold(I) and gold(III) complexes have been synthesised and their antiproliferative effects towards various cancer cell lines have been screened. The di(N-heterocyclic carbene) ligands have a propylene linker between the carbene moieties and the imidazole backbone has been functionalised with a 1-benzyl- or 1-PEG-1,2,3-triazole ring (PEG=poly(ethylene glycol)) via a CuAAC (copper azido alkyne cycloaddition) reaction. The resulting gold(I) and gold(III) complexes display an antiproliferative activity superior to that of the unfunctionalised pristine complexes together with a higher selectivity towards cancerous cells with respect to healthy cells. PMID:25226437

  14. Copper(I), silver(I) and gold(I) complexes of N-heterocyclic carbene-phosphinidene.

    PubMed

    Adiraju, Venkata A K; Yousufuddin, Muhammed; Dias, H V Rasika

    2015-03-14

    N-heterocyclic carbene stabilized phosphinidene IMes·PPh has been used as a bridging ligand to isolate a group of closely related molecules involving all three coinage metal ions. The bis-copper(I) chloride, bis-silver(I) chloride and bis-copper(I) bromide adducts of IMes·PPh crystallize as halide ion bridged octanuclear molecules while the [IMes·PPh](AuCl)2 adduct remains monomeric. These molecules feature long P-C(carbene) bonds in the range 1.822(3)-1.843(4) Å, near the typical P-C single bond length region. PMID:25410496

  15. Cationic bis-N-heterocyclic carbene (NHC) ruthenium complex: structure and application as latent catalyst in olefin metathesis.

    PubMed

    Rouen, Mathieu; Queval, Pierre; Falivene, Laura; Allard, Jessica; Toupet, Loïc; Crévisy, Christophe; Caijo, Frédéric; Baslé, Olivier; Cavallo, Luigi; Mauduit, Marc

    2014-10-13

    An unexpected cationic bis-N-heterocyclic carbene (NHC) benzylidene ether based ruthenium complex (2 a) was prepared through the double incorporation of an unsymmetrical unsaturated N-heterocyclic carbene (U2 -NHC) ligand that bore an N-substituted cyclododecyl side chain. The isolation and full characterization (including X-ray diffraction studies) of key synthetic intermediates along with theoretical calculations allowed us to understand the mechanism of the overall cationization process. Finally, the newly developed complex 2 a displayed interesting latent behavior during ring-closing metathesis, which could be "switched on" under acidic conditions. PMID:25212827

  16. Enantioselective Synthesis of Tertiary Propargylic Alcohols under N-Heterocyclic Carbene Catalysis.

    PubMed

    Sánchez-Díez, Eduardo; Fernández, Maitane; Uria, Uxue; Reyes, Efraim; Carrillo, Luisa; Vicario, Jose L

    2015-06-01

    A straightforward procedure to carry out the enantioselective benzoin reaction between aldehydes and ynones by employing a chiral N-heterocyclic carbene (NHC) as catalyst was developed. Under the optimized reaction conditions, these ynones undergo a clean and selective 1,2-addition with the catalytically generated Breslow intermediate, not observing any byproduct arising from competitive Stetter-type reactivity. This procedure allows the preparation of tertiary alkynyl carbinols as highly enantioenriched materials, which have the remarkable potential to be used as chiral building blocks in organic synthesis. PMID:25907587

  17. Electronic spectra of linear HC$_5$H and cumulene carbene H$_2$C$_5$

    E-print Network

    Steglich, M; Maity, S; Nagy, A; Maier, J P

    2015-01-01

    The $1 ^3\\Sigma_u^- \\leftarrow X^3\\Sigma_g^-$ transition of linear HC$_5$H (A) has been observed in a neon matrix and gas phase. The assignment is based on mass-selective experiments, extrapolation of previous results of the longer HC$_{2n+1}$H homologues, and density functional and multi-state CASPT2 theoretical methods. Another band system starting at 303 nm in neon is assigned as the $1 ^1 A_1 \\leftarrow X ^1 A_1$ transition of the cumulene carbene pentatetraenylidene H$_2$C$_5$ (B).

  18. N-Heterocyclic Carbene-Mediated Oxidative Electrosynthesis of Esters in a Microflow Cell.

    PubMed

    Green, Robert A; Pletcher, Derek; Leach, Stuart G; Brown, Richard C D

    2015-07-01

    An efficient N-heterocyclic carbene (NHC)-mediated oxidative esterification of aldehydes has been achieved in an undivided microfluidic electrolysis cell at ambient temperature. Productivities of up to 4.3 g h(-1) in a single pass are demonstrated, with excellent yields and conversions for 19 examples presented. Notably, the oxidative acylation reactions were shown to proceed with a 1:1 stoichiometry of aldehyde and alcohol (for primary alcohols), with remarkably short residence times in the electrolysis cell (<13 s), and without added electrolyte. PMID:26073623

  19. Rhodium(I)-Catalyzed Sequential C(sp)?C(sp(3) ) and C(sp(3) )?C(sp(3) ) Bond Formation through Migratory Carbene Insertion.

    PubMed

    Xia, Ying; Feng, Sheng; Liu, Zhen; Zhang, Yan; Wang, Jianbo

    2015-06-26

    A Rh(I) -catalyzed three-component reaction of tert-propargyl alcohol, diazoester, and alkyl halide has been developed. This reaction can be considered as a carbene-involving sequential alkyl and alkynyl coupling, in which C(sp)?C(sp(3) ) and C(sp(3) )?C(sp(3) ) bonds are built successively on the carbenic carbon atom. The Rh(I) -carbene migratory insertion of an alkynyl moiety and subsequent alkylation are proposed to account for the two separate C?C bond formations. This reaction provides an efficient and tunable method for the construction of all-carbon quaternary center. PMID:25982105

  20. The design and synthesis of novel IBiox N-heterocyclic carbene ligands derived from substituted amino-indanols.

    PubMed

    Levy, Jean-Noël; Latham, Christopher M; Roisin, Loïc; Kandziora, Nadine; Di Fruscia, Paolo; White, Andrew J P; Woodward, Simon; Fuchter, Matthew J

    2012-01-21

    A synthetic route towards a number of novel IBiox N-heterocyclic carbene (NHC) ligands has been developed. The resulting ligands have restricted flexibility and high steric demand. Preliminary studies have shown these ligands to give high levels of asymmetric induction in the copper-free allylic alkylation of cinnamyl bromide. PMID:22120851

  1. Synthesis of Naphthalenes through Three-Component Coupling of Alkynes, Fischer Carbene Complexes, and Benzaldehyde Hydrazones via Isoindole Intermediates

    PubMed Central

    Duan, Shaofeng; Sinha-Mahapatra, Dilip K.; Herndon, James W.

    2008-01-01

    The synthesis of naphthalene derivatives through three-component coupling of 2-alkynylbenzaldehyde hydrazones with carbene complexes and electron-deficient alkynes has been examined. The reaction involves formation of an isoindole derivative, followed by intramolecular Diels–Alder reaction, followed by nitrene extrusion. The reaction was highly regioselective using unsymmetrical alkynes. PMID:18351767

  2. Pd-N-Heterocyclic Carbene (NHC) Organic Silica: Synthesis and Application in Carbon-Carbon Coupling Reactions

    EPA Science Inventory

    The first Pd-N-heterocyclic carbene (NHC) complex in the form of organic silica was prepared using sol-gel method and its application in Heck and Suzuki reaction were demonstrated. These C-C coupling reactions proceeded efficiently under the influence of microwave irradiation, wi...

  3. Nickel N-heterocyclic carbene catalyzed c?c bond formation: a new route to aryl ketones.

    PubMed

    Gu, Li-Jun; Jin, Cheng; Zhang, Hong-Tao

    2015-06-01

    A novel nickel N-heterocyclic carbene catalyzed cross-coupling reaction of aryl aldehydes with boronic esters for the synthesis of aryl ketones was developed. This reaction provides a mild, practical method toward aryl ketones, which are versatile intermediates and building blocks in organic synthesis. PMID:25925163

  4. Optimized Syntheses of Cyclopentadienyl Nickel Chloride Compounds Containing "N"-Heterocyclic Carbene Ligands for Short Laboratory Periods

    ERIC Educational Resources Information Center

    Cooke, Jason; Lightbody, Owen C.

    2011-01-01

    Experiments are described for the preparation of imidazolium chloride precursors to "N"-heterocyclic carbenes and their cyclopentadienyl nickel chloride derivatives. The syntheses have been optimized for second- and third-year undergraduate laboratories that have a maximum programmed length of three hours per week. The experiments are flexible and…

  5. Copolymerization of cyclohexene oxide with CO2 catalyzed by tridentate N-heterocyclic carbene titanium(IV) complexes.

    PubMed

    Quadri, Coralie C; Le Roux, Erwan

    2014-03-21

    A new class of complexes based on titanium(IV) bearing a bisanionic mer-tridentate N-heterocyclic carbene ligand were investigated for the copolymerization of cyclohexene oxide with CO2. Upon addition of [PPN]X' salts, all complexes were found to be active and highly selective toward the formation of poly(cyclohexene oxide-alt-carbon dioxide). PMID:24292280

  6. Bis-mixed-carbene ruthenium-thiolate-alkylidene complexes: synthesis and olefin metathesis activity.

    PubMed

    Dahcheh, Fatme; Stephan, Douglas W

    2015-01-28

    A series of bis-carbene Ru-hydride species, including (IMes)(Im(OMe)2)(PPh3)RuHCl (1) and (SIMes)(Me2Im(OMe)2)(PPh3)RuHCl (2) were prepared and subsequently shown to react with aryl-vinyl-sulfides to give the bis-carbene-alkylidene complexes: Im(OMe)2(SIMes)RuCl(SR)(=CHCH3) (R = p-FC6H4 (3), p-(NO2)C6H4 (4)), Im(OMe)2(IMes)RuCl(=CHCH3)(SPh) (5), Me2Im(OMe)2(SIMes)RuCl(=CHCH3)(SPh) (6), Im(OMe)2(SIMes)(F5C6S)RuCl(=CHR) (R = C4H9 (9), C5H11 (10)). The activity of these species in the standard Grubbs' tests for ring-opening metathesis polymerization, ring-closing and cross-metathesis are reported. Although these thiolate derivatives are shown to exhibit modest metathesis activities, the reactivity is enhanced in the presence of BCl3. PMID:25462569

  7. Stretch Out or Fold Back? Conformations of Dinuclear Gold(I) N-Heterocyclic Carbene Macrocycles.

    PubMed

    Kobialka, Stefanie; Müller-Tautges, Christina; Schmidt, Melanie T S; Schnakenburg, Gregor; Hollóczki, Oldamur; Kirchner, Barbara; Engeser, Marianne

    2015-07-01

    We report the synthesis and characterization of 12 new dinuclear gold(I) N-heterocyclic carbene (NHC) complexes and the corresponding imidazolium precursors. The focus lies in a systematic study of conformational changes and intra- and intermolecular gold-gold and ?-? interactions of dinuclear gold(I) carbene complexes. Common to all members of the series of gold macrocycles are NHC ligands on the basis of imidazole with ethyl side chains and bromide as well as hexafluorophosphate counterions, respectively. The compounds vary in the length of a flexible alkyl linker between the NHC units. For the methylene and ethylene bridged macrocycles, a ring inversion movement can be observed by VT-NMR. In total, 11 molecular structures have been characterized by X-ray diffraction. Open ring conformations with intermolecular ?-? and Au-Au interactions prevail, but a backfolded conformation with a short intramolecular Au-Au distance has been found for the ethylene-bridged species. The presence of Au-Au interactions could be proven by quantum chemical calculations. PMID:26087332

  8. A one-pot combination of amine and heterocyclic carbene catalysis: direct asymmetric synthesis of ?-hydroxy and ?-malonate esters from ?,?-unsaturated aldehydes

    Microsoft Academic Search

    Gui-Ling Zhao; Armando Córdova

    2007-01-01

    The one-pot combination of amine and heterocyclic carbene catalysis (AHCC) enabled the synthesis of ?-hydroxy, ?-malonate and ?-amino esters from ?,?-unsaturated aldehydes with high enantioselectivity (91–97% ee).

  9. What difference one double bond makes: Electronic structure of saturated and unsaturated n-heterocyclic carbene ligands in Grubbs 2nd generation-type catalysts

    Microsoft Academic Search

    Richard L. Lord; Huijun Wang; Mario Vieweger; Mu-Hyun Baik

    2006-01-01

    N-heterocyclic carbene (NHC) ligands are a versatile and useful class of ligands that have enjoyed much success over the past few decades in organometallic chemistry. This fact is exemplified most convincingly in Grubbs 2nd generation olefin metathesis catalysts. We explore the electronic impact of the NHC-ligand by decoupling electronic and steric effects through simplified model N-heterocyclic carbenes. Saturated and unsaturated

  10. Exploiting Acyl and Enol Azolium Intermediates via NHeterocyclic Carbene Catalyzed Reactions of Alpha-Reducible Aldehydes

    PubMed Central

    Vora, Harit U.; Wheeler, Philip

    2013-01-01

    N-heterocyclic carbenes are well known for their role in catalyzing benzoin and Stetter reactions: the generation of acyl anion equivalents from simple aldehydes to react with a variety of electrophiles. However, when an aldehyde bearing a leaving group or unsaturation adjacent to the acyl anion equivalent is subjected to an NHC, a new avenue of reactivity is unlocked, leading to a number of novel transformations which can generate highly complex products from simple starting materials, many of which are assembled through unconventional bond disconnections. The field of these new reactions - those utilizing ?-reducible aldehydes to access previously unexplored catalytic intermediates – has expanded rapidly in the past eight years. This review aims to provide the reader with a historical perspective on the underlying discoveries that led to the current state of the art, a mechanistic description of these reactions, and a summary of the recent advances in this area. PMID:23538785

  11. Cyclic alkyl amino carbene (CAAC) ruthenium complexes as remarkably active catalysts for ethenolysis.

    PubMed

    Marx, Vanessa M; Sullivan, Alexandra H; Melaimi, Mohand; Virgil, Scott C; Keitz, Benjamin K; Weinberger, David S; Bertrand, Guy; Grubbs, Robert H

    2015-02-01

    An expanded family of ruthenium-based metathesis catalysts bearing cyclic alkyl amino carbene (CAAC) ligands was prepared. These catalysts exhibited exceptional activity in the ethenolysis of the seed-oil derivative methyl oleate. In many cases, catalyst turnover numbers (TONs) of more than 100,000 were achieved, at a catalyst loading of only 3?ppm. Remarkably, the most active catalyst system was able to achieve a TON of 340,000, at a catalyst loading of only 1?ppm. This is the first time a series of metathesis catalysts has exhibited such high performance in cross-metathesis reactions employing ethylene gas, with activities sufficient to render ethenolysis applicable to the industrial-scale production of linear ?-olefins (LAOs) and other terminal-olefin products. PMID:25522160

  12. Intramolecular C-N bond activation and ring-expansion reactions of N-heterocyclic carbenes.

    PubMed

    Hemberger, Patrick; Bodi, Andras; Berthel, Johannes H J; Radius, Udo

    2015-01-19

    Intramolecular ring-expansion reactions (RER) of the N-heterocyclic carbene 1,3-dimethylimidazolin-2-ylidene were observed upon vacuum ultraviolet (VUV) photoexcitation. Similarly to RERs reported in the solvent phase, for the reaction of NHCs with main-group-element hydrides, hydrogen transfer to the NHC carbon atom is the crucial initial step. In an ionization-mediated protonation, 1,3-dimethylimidazolin-2-ylidene forms an imidazolium ion, which is the rate-limiting step on the pathway to two six-membered ring products, namely, methylpyrimidinium and -pyrazinium ions. To unravel the reaction path, we have used imaging photoelectron photoion coincidence spectroscopy with VUV synchrotron radiation, as well as high-level composite method calculations. Similarities and differences between the mechanism in the gas phase and in the condensed phase are discussed. PMID:25430962

  13. Photoswitchable organocatalysis: using light to modulate the catalytic activities of N-heterocyclic carbenes.

    PubMed

    Neilson, Bethany M; Bielawski, Christopher W

    2012-08-01

    A 4,5-dithienylimidazolium salt was found to undergo electrocyclic isomerization upon exposure to UV radiation (?(irr) = 313 nm) under neutral and basic conditions; subsequent exposure to visible light reversed the reaction. Under ambient light and in the presence of base, the imidazolium species catalyzed transesterifications as well as amidations in a manner similar to those of previously reported N-heterocyclic carbene precatalysts. However, upon UV irradiation to effect the aforementioned photocyclization, the rate of the transesterification reaction between vinyl acetate and allyl alcohol was significantly attenuated (k(vis/UV) = 12.5), as was the rate of the condensation of ethyl acetate with aminoethanol (k(vis/UV) = 100). The rates of these reactions were successfully toggled between fast and slow states by alternating exposure to visible and UV light, respectively, thus demonstrating a rare example of a photoswitchable catalyst that operates via photomodulation of its electronic structure. PMID:22809240

  14. Gas Phase Studies of N-Heterocyclic Carbene-Catalyzed Condensation Reactions.

    PubMed

    Tian, Yuan; Lee, Jeehiun K

    2015-07-01

    N-Heterocyclic carbenes (NHCs) catalyze Umpolung condensation reactions of carbonyl compounds, including the Stetter reaction. These types of reactions have not heretofore been examined in the gas phase. Herein, we explore the feasibility of examining these reactions in the absence of solvent. A charge-tagged thiazolylidene catalyst is used to track the reactions by mass spectrometry. We find that the first Umpolung step, the addition of the NHC catalyst to a carbonyl compound to form the "Breslow intermediate", does not readily proceed in the gas phase, contrary to the case in solution. The use of acylsilanes in place of the carbonyl compounds appears to solve this issue, presumably because of a favorable Brook rearrangement. The second addition reaction, with enones, does not occur under our gas phase conditions. These reactions do occur in solution; the differential reactivity between the condensed and gas phases is discussed, and calculations are used to aid in the interpretation of the results. PMID:26066314

  15. Cationic iridium(III) complexes with two carbene-based cyclometalating ligands: cis versus trans isomers.

    PubMed

    Monti, Filippo; La Placa, Maria Grazia I; Armaroli, Nicola; Scopelliti, Rosario; Grätzel, Michael; Nazeeruddin, Mohammad Khaja; Kessler, Florian

    2015-03-16

    A series of cationic iridium(III) complexes with two carbene-based cyclometalating ligands and five different N^N bipyridine and 1,10-phenanthroline ancillary ligands is presented. For the first time--in the frame of a rarely studied class of bis(heteroleptic) iridium complexes with two carbene-based cyclometalating ligands--a pair of cis and trans isomers has been isolated. All complexes (trans-1-5 and cis-3) were characterized by (1)H NMR, (13)C NMR, (31)P NMR, and HRMS (ESI-TOF); in addition, crystal structures of cis-3 and trans-4 are reported and discussed. Cyclic voltammetric studies show that the whole series exhibits highly reversible oxidation and reduction processes, suggesting promising potential for optoelectronic applications. Ground-state DFT and TD-DFT calculations nicely predict the blue shift experimentally observed in the room-temperature absorption and emission spectra of cis-3, compared to the trans complexes. In CH3CN, cis-3 displays a 4-fold increase in photoluminescence quantum yield (PLQY) with respect to trans-3, as a consequence of drastically slower nonradiative rate constant. By contrast, at 77 K, the emission properties of all the compounds, including the cis isomer, are much more similar, with a pronounced hypsochromic shift for the trans complexes. A similar behavior is found in solid state (1% w/w poly(methyl methacrylate) matrix), with all complexes displaying PLQY of ?70-80%, comparable emission lifetimes (? ? 1.3 ?s), and a remarkable rigidochromic shift. To rationalize the more pronounced nonradiative deactivation (and smaller PLQY) observed for photoexcited trans complexes, comparative temperature-dependent emission studies in the range of 77-450 K for cis-3 and trans-3 were made in propylene glycol, showing that solvation effects are primarily responsible for the observed behavior. PMID:25741900

  16. Synthesis, characterization, and antileishmanial activities of gold(I) complexes involving quinoline functionalized N-heterocyclic carbenes.

    PubMed

    Paloque, Lucie; Hemmert, Catherine; Valentin, Alexis; Gornitzka, Heinz

    2015-04-13

    A series of new mononuclear cationic or neutral gold(I) complexes containing quinoline functionalized N-heterocyclic carbene(s) (NHC(s)) were synthesized and fully characterized by spectroscopic methods. The X-ray structures of two key compounds are presented. Proligands and their corresponding gold(I) complexes together with previously described silver(I) and gold(I) bis(NHC-quinoline) and gold(I) bis(NHC-methylbipyridine) complexes were evaluated in vitro towards Leishmania infantum. In parallel, the in vitro cytotoxicity of these molecules was assessed on the murine macrophages J774A.1. All gold(I) compounds show potent antileishmanial activity against L. infantum promastigotes and three of them are also efficient against L. infantum intracellular amastigotes. Structure-activity and toxicity relationships enables to evidence a lead-compound (6) displaying both a high activity and a good selectivity index. PMID:25747497

  17. Rate and Equilibrium Constants for the Addition of N-Heterocyclic Carbenes into Benzaldehydes: A Remarkable 2-Substituent Effect**

    PubMed Central

    Collett, Christopher J; Massey, Richard S; Taylor, James E; Maguire, Oliver R; O'Donoghue, AnnMarie C; Smith, Andrew D

    2015-01-01

    Rate and equilibrium constants for the reaction between N-aryl triazolium N-heterocyclic carbene (NHC) precatalysts and substituted benzaldehyde derivatives to form 3-(hydroxybenzyl)azolium adducts under both catalytic and stoichiometric conditions have been measured. Kinetic analysis and reaction profile fitting of both the forward and reverse reactions, plus onwards reaction to the Breslow intermediate, demonstrate the remarkable effect of the benzaldehyde 2-substituent in these reactions and provide insight into the chemoselectivity of cross-benzoin reactions. PMID:25908493

  18. Luminescence Studies of the Intracellular Distribution of a Dinuclear Gold(I) N-Heterocyclic Carbene Complex

    SciTech Connect

    Barnard, Peter J.; Wedlock, Louise E.; Baker, Murray V.; Berners-Price, Susan J.; Joyce, David A.; Skelton, Brian W.; Steer, James H. (UWA)

    2008-10-03

    A bidentate cyclophane N-heterocyclic carbene ligand has been used to synthesize a new dinuclear Au{sup I} complex of the formula [Au{sub 2}L{sub 2}]{sup 2+}. The short Au {hor_ellipsis} Au distance imposed by the rigid cyclophane ligand leads to a red-shifted luminescence profile that enables the complex to be used as a luminescent probe for distribution studies in single living cancer cells.

  19. Oxidative N-Heterocyclic Carbene-Catalyzed ?-Carbon Addition of Enals to Imines: Mechanistic Studies and Access to Antimicrobial Compounds.

    PubMed

    Zheng, Peng-Cheng; Cheng, Jiajia; Su, Shihu; Jin, Zhichao; Wang, Yu-Huang; Yang, Song; Jin, Lin-Hong; Song, Bao-An; Chi, Yonggui Robin

    2015-07-01

    The reaction mechanism of the ?-carbon addition of enal to imine under oxidative N-heterocyclic carbene catalysis is studied experimentally. The oxidation, ?-carbon deprotonation, and nucleophilic addition of ?-carbon to imine were found to be facile steps. The results of our study also provide highly enantioselective access to tricyclic sulfonyl amides that exhibit interesting antimicrobial activities against X. oryzae, a bacterium that causes bacterial disease in rice growing. PMID:26037373

  20. Energy Transfer in a Hybrid Ir(III) Carbene-Pt(II) Acetylide Assembly for Efficient Hydrogen Production.

    PubMed

    Yu, Zhen-Tao; Yuan, Yong-Jun; Chen, Xin; Cai, Jian-Guang; Zou, Zhi-Gang

    2015-07-01

    A new heterometallic supramolecular complex, consisting of an iridium carbene-based unit appended to a platinum terpyridine acetylide unit, representing a new Ir(III) -Pt(II) structural motif, was designed and developed to act as an active species for photocatalytic hydrogen production. The results also suggested that a light-harvesting process is essential to realize the solar-to-fuel conversion in an artificial system as illustrated in the natural photosynthetic system. PMID:26096270

  1. Preparation of a N-Heterocyclic Carbene Nickel(II) Complex: Synthetic Experiments in Current Organic and Organometallic Chemistry

    ERIC Educational Resources Information Center

    Ritleng, Vincent; Brenner, Eric; Chetcuti, Michael J.

    2008-01-01

    A four-part experiment that leads to the synthesis of a cyclopentadienyl chloro-nickel(II) complex bearing a N-heterocyclic carbene (NHC) ligand is presented. In the first part, the preparation of 1,3-bis-(2,4,6-trimethylphenyl)imidazolium chloride (IMes[middle dot]HCl) in a one-pot procedure by reaction of 2,4,6-trimethylaniline with…

  2. Catalytic Enantioselective Total Syntheses of Bakkenolides I, J and S: Application of a Carbene-Catalyzed Desymmetrization

    PubMed Central

    Phillips, Eric M.; Roberts, John M.; Scheidt, Karl A.

    2010-01-01

    A general strategy for the catalytic asymmetric syntheses of the bakkenolides is reported. The key bond-forming step involves an N-heterocyclic carbene catalyzed desymmetrization of a 1,3-diketone to form three new bonds in one step with excellent enantio– and diastereoselectivity. This intramolecular reaction allows direct access to the hydrindane core of the bakkenolides family and enables a facile synthesis of these natural products. PMID:20469924

  3. Air-Stable (CAAC)CuCl and (CAAC)CuBH4 Complexes as Catalysts for the Hydrolytic Dehydrogenation of BH3 NH3.

    PubMed

    Hu, Xingbang; Soleilhavoup, Michèle; Melaimi, Mohand; Chu, Jiaxiang; Bertrand, Guy

    2015-05-11

    The first stable copper borohydride complex [(CAAC)CuBH4 ] [CAAC=cyclic(alkyl)(amino)carbene] bearing a single monodentate ligand was prepared by addition of NaBH4 or BH3 NH3 to the corresponding [(CAAC)CuCl] complex. Both complexes are air-stable and promote the catalytic hydrolytic dehydrogenation of ammonia borane. The amount of hydrogen released reaches 2.8 H2 /BH3 NH3 with a turnover frequency of 8400?mol?H?2?molcat (-1) ?h(-1) at 25?°C. In a fifteen-cycle experiment, the catalyst was reused without any loss of efficiency. PMID:25802096

  4. "Hummingbird" Behaviour of N-Heterocyclic Carbenes Stabilises Out-of-Plane Bonding of AuCl and CuCl Units.

    PubMed

    Teci, Matthieu; Brenner, Eric; Matt, Dominique; Gourlaouen, Christophe; Toupet, Loic

    2015-07-27

    An N-heterocyclic carbene substituted by two expanded 9-ethyl-9-fluorenyl groups was shown to bind an AuCl unit in an unusual manner, namely with the Au?X rod sitting out of the plane defined by the heterocyclic carbene unit. As shown by X-ray studies and DFT calculations, the observed large pitch angle (21°) arises from an easy displacement of the gold(I) atom away from the carbene lone-pair axis, combined with the stabilisation provided by weak CH???Au interactions involving aliphatic and aromatic H atoms of the NHC wingtips. Weak, intermolecular Cl???H bonds are likely to cooperate with the H???Au interactions to stabilise the out-of-plane conformation. A general belief until now was that tilt angles in NHC complexes arise mainly from steric effects within the first coordination sphere. PMID:26130507

  5. Recent advances in carbon dioxide capture, fixation, and activation by using N-heterocyclic carbenes.

    PubMed

    Yang, Longhua; Wang, Hongming

    2014-04-01

    In the last two decades, CO2 emission has caused a lot of environmental problems. To mitigate the concentration of CO2 in the atmosphere, various strategies have been implemented, one of which is the use of N-heterocyclic carbenes (NHCs) and related complexes to accomplish the capture, fixation, and activation of CO2 effectively. In this review, we summarize CO2 capture, fixation, and activation by utilizing NHCs and related complexes; homogeneous reactions and their reaction mechanisms are discussed. Free NHCs and NHC salts can capture CO2 in both direct and indirect ways to form imidazolium carboxylates, and they can also catalyze the reaction of aromatic aldehydes with CO2 to form carboxylic acids and derivatives. Moreover, associated with transition metals (TMs), NHCs can form NHC-TM complexes to transform CO2 into industrial acid or esters. Non-metal-NHC complexes can also catalyze the reactions of silicon and boron complexes with CO2 . In addition, catalytic cycloaddition of epoxides with CO2 is another effective function of NHC complexes, and NHC ionic liquids perform excellently in this aspect. PMID:24644039

  6. Nanofiber composites containing N-heterocyclic carbene complexes with antimicrobial activity.

    PubMed

    Elzatahry, Ahmed A; Al-Enizi, Abdullah M; Elsayed, Elsayed Ahmed; Butorac, Rachel R; Al-Deyab, Salem S; Wadaan, Mohammad A M; Cowley, Alan H

    2012-01-01

    This report concerns nanofiber composites that incorporate N-heterocyclic carbenes and the use of such composites for testing antimicrobial and antifungal activities. The nanofiber composites were produced by electrospinning mixtures of the gold chloride or gold acetate complexes of a bis(imino)acenaphthene (BIAN)-supported NHC with aqueous solutions of polyvinyl alcohol (PVA). The products were characterized by scanning-electron microscopy, which revealed that nanofibers in the range of 250-300 nm had been produced. The biological activities of the nanofiber composites were tested against two Gram-positive bacteria, six Gram-negative bacteria, and two fungal strains. No activity was evident against the fungal strains. However, the gold chloride complex was found to be active against all the Gram-positive pathogens and one of the Gram-negative pathogens. It was also found that the activity of the produced nanofibers was localized and that no release of the bioactive compound from the nanofibers was evident. The demonstrated antimicrobial activities of these novel nanofiber composites render them potentially useful as wound dressings. PMID:22745545

  7. ?,?-Unsaturated Acyl Azoliums from N-Heterocyclic Carbene Catalyzed Reactions: Observation and Mechanistic Investigation**

    PubMed Central

    Mahatthananchai, Jessada; Zheng, Pinguan; Bode, Jeffrey W.

    2011-01-01

    Catalytically generated acyl azoliums I and their ?,?-unsaturated counterparts II are thought to be key reactive intermediates in a rapidly growing number of transformations promoted by N-heterocyclic carbene (NHC) catalysts.[1] Acyl azoliums are invoked in the postulated catalytic cycles of nearly all of the new NHC-catalyzed reactions of ?-functionalized aldehydes reported since 2004, in which they are generally assumed to possess the reactivity of an activated carboxylic acid, that is, analogous to an activated ester.[2] In NHC-catalyzed processes, they are most often obtained through internal redox reactions of functionalized aldehydes but have also been prepared by oxidations of the Breslow intermediates[3] or additions to ketenes.[4] Acyl azoliums I are important intermediates in thiamine pyrophosphate (ThPP) dependent enzymatic reactions.[5] Townsend et al. have recently proposed that unsaturated acyl azolium III is the key intermediate in clavulanic acid biosynthesis;[6] despite careful efforts, III or its analogues II have never been characterized or independently synthesized. Here, we document the observation and characterization of ?,?-unsaturated acyl azoliums 1 and 2 (Scheme 1) and demonstrate that their corresponding hemiacetals (1? and 2”) are the kinetically important intermediates in both their acylation and annulation reactions. PMID:21308930

  8. Probing the Diastereoselectivity of Staudinger Reactions Catalyzed by N-Heterocyclic Carbenes.

    PubMed

    Hans, Morgan; Wouters, Johan; Demonceau, Albert; Delaude, Lionel

    2015-07-20

    The reaction of ethylphenylketene with 1,3-dimesitylimidazol-2-ylidene (IMes) or 1,3-dimesitylimidazolin-2-ylidene (SIMes) afforded the corresponding azolium enolates in high yields. The two zwitterions were fully characterized by various analytical techniques. Their thermal stabilities were monitored by thermogravimetric analysis and the molecular structure of SIMes?EtPhC?C?O was determined by means of X-ray crystallography. A mechanism was proposed to account for the trans-diastereoselectivity observed in the [2+2] cycloaddition of ketenes and N-protected imines catalyzed by N-heterocyclic carbenes and an extensive catalytic screening was performed to test its validity. The steric bulk of the NHC catalyst markedly affected the cis/trans ratio of the model ?-lactam product. The nature of the solvent used to carry out the Staudinger reaction also significantly influenced its diastereoselectivity. Conversely, the nature of the substituent on the N-sulfonated imine reagent and the reaction temperature were less critical parameters. PMID:26073307

  9. Planar N-heterocyclic carbene diarylborenium ions: synthesis by cationic borylation and reactivity with Lewis bases.

    PubMed

    Farrell, Jeffrey M; Stephan, Douglas W

    2015-04-20

    The NHC-borane adduct (IBn)BH3 (1) (NHC= N-heterocyclic carbene; IBn=1,3-dibenzylimidazol-2ylidene) reacts with [Ph3 C][B(C6 F5 )4 ] through sequential hydride abstraction and dehydrogenative cationic borylation(s) to give singly or doubly ring closed NHC-borenium salts 2 and 3. The planar doubly ring closed product [C3 H2 (NCH2 C6 H4 )2 B][B(C6 F5 )4 ] is resistant to quaternization at boron by Et2 O coordination, but forms classical Lewis acid-base adducts with the stronger donors Ph3 P, Et3 PO, or 1,4-diazabicyclo[2.2.2]octane (DABCO). Treatment of 3 with tBu3 P selectively yields the unusual oligomeric borenium salt trans-[(C3 H2 (NCH2 C6 H4 )2 B)2 (C3 H2 (NCHC6 H4 )2 B)][B(C6 F5 )4 ] (7). PMID:25756464

  10. Carbene-functionalized single-walled carbon nanotubes and their electrical properties.

    PubMed

    Liu, Chao; Zhang, Qing; Stellacci, Francesco; Marzari, Nicola; Zheng, Lianxi; Zhan, Zhaoyao

    2011-05-01

    Pure metallic single-walled carbon nanotubes (m-SWCNTs) are very desirable for many electrode and interconnecting applications. However, the lack of reliable processing techniques to sort m-SWCNTs from the as-synthesized SWCNT samples is an obstacle to these applications. The effects of carbene-based covalent functionalization on the electrical properties of an isolated m-SWCNT, a semiconducting (s)-SWCNT, and a mixture network of both m- and s-SWCNTs are reported. For the first time, a semiconducting-to-metallic SWCNT transition upon dichlorocarbene functionalization is observed. Interestingly, the transition is reversible upon thermal annealing under ambient conditions. The electrical properties of m-SWCNTs remain largely unaffected whereas the on-state conductivity of s-SWCNTs is greatly reduced by this process, in agreement with the relevant theoretical predictions. These findings could pave the way for fabricating large-scale SWCNT-based interconnects and electrodes in full-carbon integrated circuits. PMID:21485006

  11. Effects of Phosphine-Carbene Substitutions on the Electrochemical and Thermodynamic Properties of Nickel Complexes

    SciTech Connect

    Galan, Brandon R.; Wiedner, Eric S.; Helm, Monte L.; Linehan, John C.; Appel, Aaron M.

    2014-05-12

    Nickel(II) complexes containing chelating N-heterocyclic carbene-phosphine ligands ([NiL2](BPh4)2, for which L = [MeIm(CH2)2PR2]) have been synthesized for the purpose of studying how this class of ligand effects the electrochemical properties compared to the nickel bis- diphosphine analogues. The nickel complexes were synthesized and characterized by x-ray crystallography and electrochemical methods. Based on the half wave potentials (E1/2), substitution of an NHC for one of the phosphines in a diphoshine ligand results in shifts in potential to 0.6 V to 1.2 V more negative than the corresponding nickel bis-diphosphine complexes. These quantitative results highlight the substantial effect that NHC ligands can have upon the electronic properties of the metal complexes. BRG, JCL, and AMA acknowledge the support by the US Department of Energy Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. MLH acknoledges the support of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

  12. Conformation analysis of triphenylphosphine in trans and cis triphenylphosphine-substituted Fischer carbene complexes

    NASA Astrophysics Data System (ADS)

    Landman, Marilé; Levell, Tamzyn; van Rooyen, Petrus H.; Conradie, Jeanet

    2014-05-01

    The synthesis and selected crystal structures of novel (M = Cr or Mo) and known (M = W) [(CO)4(PPh3)M = C(OEt)R] complexes, M = Cr, R = 2-thienyl (1), 2-furyl (2); M = Mo, R = 2-thienyl (3), 2-furyl (4); M = W, R = 2-thienyl (5), 2-furyl (6), are presented. Experimental crystal structures and DFT calculations of selected trans- and cis-triphenylphosphine-substituted Fischer carbene complexes, illustrate that the minimum energy conformation of triphenylphosphine (PPh3) in octahedral [(CO)4(PPh3)ML]-complexes generally have distinct features that can be described in terms of the "plane of nadir energy", a plane linking all points of minimum steric compression between the ligands. The generally observed orientation of PPh3 involves a correlated feathering of the phenyl groups with the PCipso bond of one phenyl group orientated near parallel to the nadir plane, and a meta carbon (Cm) of the other two phenyl groups orientated as near as possible to the nadir plane, orthogonal to the first. Although the orientation of PPh3 in 6-trans, [(CO)4(PPh3)W = C(OEt)2-furyl], deviates from this, DFT correctly calculated the unexpected and not generally observed PPh3 orientation.

  13. Evaluation of arene ruthenium(II) N-heterocyclic carbene complexes as organometallics interacting with thiol and selenol containing biomolecules.

    PubMed

    Oehninger, Luciano; Stefanopoulou, Maria; Alborzinia, Hamed; Schur, Julia; Ludewig, Stephanie; Namikawa, Kazuhiko; Muñoz-Castro, Alvaro; Köster, Reinhard W; Baumann, Knut; Wölfl, Stefan; Sheldrick, William S; Ott, Ingo

    2013-02-01

    Metal complexes with N-heterocyclic carbene (NHC) ligands have been widely used in catalytic chemistry and are now increasingly considered for the development of new chemical tools and metal based drugs. Ruthenium complexes of the type (p-cymene)(NHC)RuCl(2) interacted with biologically relevant thiols and selenols, which resulted in the inhibition of enzymes such as thioredoxin reductase or cathepsin B. Pronounced antiproliferative effects could be obtained provided that an appropriate cellular uptake was achieved. Inhibition of tumor cell growth was accompanied by a perturbation of metabolic parameters such as cellular respiration. PMID:23149817

  14. Spiro-fused six-membered N-heterocyclic carbene: a new scaffold toward unique properties and activities.

    PubMed

    Yang, Bin-Miao; Xiang, Kai; Tu, Yong-Qiang; Zhang, Shi-Heng; Yang, Deng-Tao; Wang, Shao-Hua; Zhang, Fu-Ming

    2014-07-11

    A six-membered N-heterocyclic carbene fused with a spiro-scaffold is designed. The new NHC shows stronger ?-donation ability than typical 5-membered NHCs. This property leads to interesting reactivities of this spiro-fused six-membered NHC. For example, the NHC-BF3 Lewis pair complex can be readily prepared by using LiBF4 as the BF3 source, or through a direct bond-reconstruction of the tetrafluoroborate salt NHC·HBF4. PMID:24851922

  15. Synthesis of Pd-N-heterocyclic carbene Pd-catalyst and its application in MW-assisted Heck and Suzuki reaction

    EPA Science Inventory

    The first Pd-N-heterocyclic carbene (NHC) complex in the form of organic silica is prepared using sol-gel method and its application in Heck and Suzuki reactions are demonstrated. These C-C coupling reactions proceeded efficiently under the influence of microwave irradiation, wit...

  16. Manganese Fischer carbene chemistry: Reactions of Cp prime (CO) sub 2 Mn double bond C(OMe/OLi)R with enynes, 1-hexyne, and acrylates

    SciTech Connect

    Hoye, T.R.; Rehberg, G.M. (Univ. of Minnesota, Minneapolis (United States))

    1990-12-01

    Reactions of manganese carbene complexes, both the neutral methoxy and anionic lithoxy' versions, with {alpha},{omega}-enzymes give bicyclic cyclopropanes. The anion also reacts with 1-hexyne to give butenolide and with acrylate esters to give {gamma}-keto esters.

  17. Rhenium and technetium tricarbonyl complexes of N-heterocyclic carbene ligands.

    PubMed

    Chan, Chung Ying; Pellegrini, Paul A; Greguric, Ivan; Barnard, Peter J

    2014-10-20

    A strategy for the conjugation of N-heterocyclic carbene (NHC) ligands to biomolecules via amide bond formation is described. Both 1-(2-pyridyl)imidazolium or 1-(2-pyridyl)benzimidazolium salts functionalized with a pendant carboxylic acid group were prepared and coupled to glycine benzyl ester using 1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide. A series of 10 rhenium(I) tricarbonyl complexes of the form [ReX(CO)3(?N)] (?N is a bidentate NHC ligand, and X is a monodentate anionic ligand: Cl(-), RCO2(-)) were synthesized via a Ag2O transmetalation protocol from the Re(I) precursor compound Re(CO)5Cl. The synthesized azolium salts and Re(I) complexes were characterized by elemental analysis and by (1)H and (13)C NMR spectroscopy, and the molecular structures for one imidazolium salt and seven Re(I) complexes were determined by single-crystal X-ray diffraction. (1)H NMR and mass spectrometry studies for an acetonitrile-d3 solution of [ReCl(CO)3(1-(2-pyridyl)-3-methylimidazolylidene)] show that the monodentate chloride ligand is labile and exchanges with this solvent yielding a cationic acetonitrile adduct. For the first time the labeling of an NHC ligand with technetium-99m is reported. Rapid Tc-99m labeling was achieved by heating the imidazolium salt 1-(2-pyridyl)-3-methylimidazolium iodide and Ag2O in methanol, followed by the addition of fac-[(99m)Tc(OH2)3(CO)3](+). To confirm the structure of the (99m)Tc-labeled complex, the equivalent (99)Tc complex was prepared, and mass spectrometric studies showed that the formed Tc complexes are of the form [(99m/99)Tc(CH3CN)(CO)3(1-(2-pyridyl)-3-methylimidazolylidene)](+) with an acetonitrile molecule coordinated to the metal center. PMID:25280253

  18. Transition metal-induced activation of alkynes leading to metal carbene species: synthetic application to new ?-conjugated molecules

    NASA Astrophysics Data System (ADS)

    Abo, T.; Ohe, K.

    2008-03-01

    The in situ generation of furylcarbene complexes by means of transition metals was applied to catalytic carbene reactions, such as Wittig-type olefination and cycloisomerization reactions. In the presence of [Rh(OAc)2]2 as a catalyst and triphenylphosphine as a carbene accepter, carbonyl-ene-ynes 1a reacted with benzaldehyde to give a 2-styrylfuran derivative 3a. The reaction involving phosphine-ylide formation followed by Wittig-type olefination with aldehydes was applied to synthesis of furfurylidene-containing p-extended conjugated molecules. A Ruthenium catalyst underwent cycloisomerization of 1,2-bis(carbonylenyl)acetylene 10a,b to afford 2,2'-bifuran structures. The crystal structure of 5,5'-diphenyl-2,2'-bifuran 11b was determined by X-ray crystallography. The ORTEP drawings of 11b exhibited transoid and highly planar structure. The emission bands of the bisfuran 11b were observed at 414 and 440 nm, its quantum yield (84%) was higher than that of a similar 5,5'-diphenyl-2,2'-bithiophene.

  19. Group 6 heteroatom- and non-heteroatom-stabilized carbene complexes. beta,beta'- and alpha,beta,beta'-annulation reactions of cyclic enamines.

    PubMed

    Barluenga, José; Ballesteros, Alfredo; Bernardo De La Rúa, Ramón; Santamaría, Javier; Rubio, Eduardo; Tomás, Miguel

    2003-02-19

    Cyclization reactions of group 6 Fischer carbene complexes with cyclopentanone and cyclohexanone enamines are described. Enamine 3a undergoes thermal alpha,beta,beta'-annulation with alkenylcarbene complexes 1 and 2 (THF, 60 degrees C), affording semibullvalenes 5. The metalate intermediates 6, resulting from beta,beta'-annulation of the enamines 3a and 4a, were quantitatively formed by running the reaction in hexane at room temperature. Acid-promoted demetalation of 6 afforded endo-2-bicyclo[3.2.1]octen-8-ones 7 and endo/exo-2-bicyclo[3.3.1]nonen-9-ones 8 (endo/exo = 5:1). Using (S)-methoxymethylpyrrolidine-derived enamines 3b and 4b,c allowed highly enantioenriched cycloadducts endo-(+)-7 as well as endo-(-)-8 and exo-(-)-8 to be accessed. The non-heteroatom-stabilized carbene complex 10 was formed from complex 6 by Me(3)SiOTf-promoted elimination of the methoxy group, characterized by (13)C NMR, and transformed into the organic compounds 7, 7-d, and 11 as well as into bicyclo[3.2.1]octan-2,8-diones 14 and cycloheptanones 15. On the basis of this sequence, enantioenriched cycloheptanones (+)-15 were efficiently prepared in one pot from carbene complexes 2 and enamine 3b (51-55% yield, 91-96% ee). Extension of this work to simple Fischer carbene complexes 16 allowed an appropriate way to generate the nonstabilized pentacarbonyl[(phenyl(alkyl)carbene]tungsten complex 17 to be designed, for which the thermal and chemical behavior leading to compounds 18-21 is described. PMID:12580610

  20. Reactivity of Cationic Agostic and Carbene Structures Derived from Platinum(II) Metallacycles.

    PubMed

    Campos, Jesús; Ortega-Moreno, Laura; Conejero, Salvador; Peloso, Riccardo; López-Serrano, Joaquín; Maya, Celia; Carmona, Ernesto

    2015-06-01

    This paper describes the formation of new platinacyclic complexes derived from the phosphine ligands PiPr2 Xyl, PMeXyl2 , and PMe2 Ar?Xyl?2 (Xyl=2,6-Me2 C6 H3 and Ar?Xyl?2=2,6-(2,6-Me2 C6 H3 )2 -C6 H3 ) as well as reactivity studies of the trans-[Pt(C^P)2 ] bis-metallacyclic complex 1?a derived from PiPr2 Xyl. Protonation of compound 1?a with [H(OEt2 )2 ][BArF ] (BArF =B[3,5-(CF3 )2 C6 H3 ]4 ) forms a cationic ?-agostic structure 4?a, whereas ?-hydride abstraction employing [Ph3 C][PF6 ] produces a cationic platinum carbene trans-[Pt{PiPr2 (2,6-CH(Me)C6 H3 }{PiPr2 (2,6-CH2 (Me)C6 H3 }][PF6 ] (8). Compounds 4?a and 8 react with H2 to yield the same 1:3 equilibrium mixture of 4?a and trans-[PtH(PiPr2 Xyl)2 ][BArF ] (6), in which one of the phosphine ligands participates in a ?-agostic interaction. DFT calculations reveal that H2 activation by 8 occurs at the highly electrophilic alkylidene terminus with no participation of the metal. The two compounds 4?a and 8 experience C-C coupling reactions of a different nature. Thus, 4?a gives rise to complex trans-[PtH{(E)-1,2-bis(2-(PiPr2 )-3-MeC6 H3 )CH?CH}] (7) that contains a tridentate diphosphine-alkene ligand, through agostic C?H oxidative cleavage and C-C reductive coupling steps, whereas the C-C coupling reaction in 8 involves classical migratory insertion of its [Pt?CH] and [Pt?CH2 ] bonds promoted by platinum coordination of CO or CNXyl. The mechanisms of the C?C bond-forming reactions have also been investigated by computational methods. PMID:25959723

  1. Transient Palladadiphosphanylcarbenes: Singlet Carbenes with an “Inverse” Electronic Configuration (p?2 instead of ?2) and Unusual Transannular Metal–Carbene Interactions (?C?pd Donation and ?Pd?C Back-donation)

    PubMed Central

    Vignolle, Joan; Gornitzka, Heinz; Maron, Laurent; Schoeller, Wolfgang W.; Bourissou, Didier; Bertrand, Guy

    2008-01-01

    Upon treatment with [PdCl(allyl)]2, asymmetrically substituted ?, ??-diphosphanyl diazo compounds eliminate dinitrogen to afford C-chlorodiphosphanylmethanide complexes in high yields. In the presence of a chloride-abstracting agent, such as sodium tetraphenylborate, the C-chlorodiphosphanylmethanide complexes react with pyridine and trimethylphosphine, readily affording the corresponding nitrogen and phosphorus ylides. The postulated intermediate in this process, namely palladadiphosphanylcarbenes, could not be spectroscopically characterized, but their transient formation was chemically supported further by a Lewis base exchange reaction between pyridine and 4-dimethylaminopyridine. This hypothesis has also been substantiated by computing the corresponding dissociation energy using two model systems featuring methyl groups at the phosphorus. Of particular interest, density functional theory calculations reveal that these palladadiphosphanylcarbenes have a singlet ground state with an “inverse” p?2 electronic configuration and a distorted geometry associated with unusual transannular metal–carbene interactions (?C?Pd donation and ?Pd?C back-donation). PMID:17243835

  2. Synthesis, Characterization, and Theoretical Investigation of Two-Coordinate Palladium(0) and Platinum(0) Complexes Utilizing ?-Accepting Carbenes.

    PubMed

    Roy, Sudipta; Mondal, Kartik Chandra; Meyer, Jann; Niepötter, Benedikt; Köhler, Christian; Herbst-Irmer, Regine; Stalke, Dietmar; Dittrich, Birger; Andrada, Diego M; Frenking, Gernot; Roesky, Herbert W

    2015-06-22

    An elegant general synthesis route for the preparation of two coordinate palladium(0) and platinum(0) complexes was developed by reacting commercially available tetrakis(triphenylphosphine)palladium/platinum with ?-accepting cyclic alkyl(amino) carbenes (cAACs). The complexes are characterized by NMR spectroscopy, mass spectrometry, and single-crystal X-ray diffraction. The palladium complexes exhibit sharp color changes (crystallochromism) from dark maroon to bright green if the C-Pd-C bond angle is sharpened by approximately 6°, which is chemically feasible by elimination of one lattice THF solvent molecule. The analogous dark orange-colored platinum complexes are more rigid and thus do not show this phenomenon. Additionally, [(cAAC)2 Pd/Pt] complexes can be quasi-reversibly oxidized to their corresponding [(cAAC)2 Pd/Pt](+) cations, as evidenced by cyclic voltammetry measurements. The bonding and stability are studied by theoretical calculations. PMID:25940809

  3. Synthesis and anticancer activity of silver(I)-N-heterocyclic carbene complexes derived from the natural xanthine products caffeine, theophylline and theobromine.

    PubMed

    Mohamed, Heba A; Lake, Benjamin R M; Laing, Thomas; Phillips, Roger M; Willans, Charlotte E

    2015-04-28

    A new library of silver(I)-N-heterocyclic carbene complexes prepared from the natural products caffeine, theophylline and theobromine is reported. The complexes have been fully characterised using a combination of NMR spectroscopy, mass spectrometry, elemental analysis and X-ray diffraction analysis. Furthermore, the hydrophobicity of the complexes has been measured. The silver(I)-N-heterocyclic carbenes have been evaluated for their antiproliferative properties against a range of cancer cell lines of different histological types, and compared to cisplatin. The data shows different profiles of response when compared to cisplatin in the same panel of cells, indicating a different mechanism of action. Furthermore, it appears that the steric effect of the ligand and the hydrophobicity of the complex both play a role in the chemosensitivity of these compounds, with greater steric bulk and greater hydrophilicity delivering higher cytotoxicity. PMID:25812062

  4. N-Heterocyclic Carbene-Catalyzed Oxidative Annulations of ?,?-Unsaturated Aldehydes with Hydrazones: Selective Synthesis of Optically Active 4,5-Dihydropyridazin-3-ones and Pyridazin-3-ones.

    PubMed

    Mao, Jian-Hui; Wang, Zi-Tian; Wang, Zhan-Yong; Cheng, Ying

    2015-06-19

    A novel and efficient method for the highly enantioselective synthesis of chiral 4,5-dihydropyridazin-3-one derivatives has been developed based on the chiral N-heterocyclic carbene-catalyzed oxidative annulation between ?,?-unsaturated aldehydes and hydrazones. Meanwhile, the selective synthesis of either 4,5-dihydropyridazin-3-ones or pyridazin-3-one derivatives from the same reactants has been achieved by simply varying catalytic and reaction conditions. PMID:26019007

  5. Luminescent Ruthenium(II) Complex Bearing Bipyridine and N-Heterocyclic Carbene-based C?N?C Pincer Ligand for Live-Cell Imaging of Endocytosis

    NASA Astrophysics Data System (ADS)

    Tsui, Wai-Kuen; Chung, Lai-Hon; Wong, Matthew Man-Kin; Tsang, Wai-Him; Lo, Hoi-Shing; Liu, Yaxiang; Leung, Chung-Hang; Ma, Dik-Lung; Chiu, Sung-Kay; Wong, Chun-Yuen

    2015-03-01

    Luminescent ruthenium(II)-cyanide complex with N-heterocyclic carbene pincer ligand C?N?C = 2,6-bis(1-butylimidazol-2-ylidene)pyridine and 2,2'-bipyridine (bpy) shows minimal cytotoxicity to both human breast carcinoma cell (MCF-7) and human retinal pigmented epithelium cell (RPE) in a wide range of concentration (0.1-500 ?M), and can be used for the luminescent imaging of endocytosis of the complex in these cells.

  6. N-Heterocyclic carbene-phosphino-picolines as precursors of anionic 'pincer' ligands with dearomatised pyridine backbones; transmetallation from potassium to chromium.

    PubMed

    Simler, Thomas; Danopoulos, Andreas A; Braunstein, Pierre

    2015-06-18

    Deprotonation of the ?-picolinyl-CH2 in the hybrid ligands R2P-NCNHC (-N = substituted 2-picoline, R = Cy, t-Bu; CNHC = N-heterocyclic carbene) () with KN(SiMe3)2 in ether gave [KL(ether)]2 featuring a dearomatised picoline backbone. Assisted by 18-crown-6, K(+) dissociation afforded the Z- and E-isomers of [L](-). Transmetallation of L from KL led to [CrCl(L)]. PMID:26050938

  7. Stereogenic-at-Metal Zn- and Al-based N-Heterocyclic Carbene (NHC) Complexes as Bifunctional Catalysts in Cu-Free Enantioselective Allylic Alkylations

    PubMed Central

    Lee, Yunmi; Li, Bo; Hoveyda, Amir H.

    2009-01-01

    Investigations detailed herein demonstrate the ability of chiral bidentate N-heterocyclic carbenes to promote directly – without the need for a Cu salt – site- and enantioselective C–C bond forming reactions. Within this context, catalytic allylic alkylations of various allylic phosphates with dialkylzinc and trialkylaluminum reagents, performed with chiral bidentate imidazolinium salts and in the absence of a Cu salt, are described. The Cu-free transformations deliver products bearing tertiary or (all-carbon) quaternary stereogenic centers with exceptional site- (>98:<2 SN2?:SN2) and high enantioselectivity [up to 97.5:2.5 enantiomer ratio (er)]. A chiral Zn-based N-heterocyclic carbene (NHC) complex, which serves as the catalyst for the enantioselective allylic alkylation reactions, is isolated and fully characterized. Spectroscopic and X-ray crystallographic studies indicate that the sulfonate group within the stereogenic-at-Zn bidentate complexes coordinates syn to the proximal phenyl substituent of the NHC backbone (vs the initially expected anti). Investigations regarding a related chiral NHC–Al based complex reveal similar structural attributes. The studies outlined provide a plausible rationale regarding the mechanism of Cu-free allylic alkylation reactions that involve dialkylzinc or trialkylaluminum reagents as well as the previously reported alkylmagnesium halides. Based on the research disclosed, it is proposed that bidentate metal-carbene complexes can serve as effective bifunctional catalysts, a critical attribute that differentiates such NHC-based complexes from the corresponding monodentate variants. PMID:19630406

  8. Cooperativity of anion⋯? and ?⋯? interactions regulates the self-assembly of a series of carbene proligands: Towards quantitative analysis of intermolecular interactions with Hirshfeld surface

    NASA Astrophysics Data System (ADS)

    Samanta, Tapastaru; Dey, Lingaraj; Dinda, Joydev; Chattopadhyay, Shyamal Kumar; Seth, Saikat Kumar

    2014-06-01

    The cooperative effect of weak non-covalent forces between anions and electron deficient aromatics by ?⋯? stacking of a series of carbene proligands (1-3) have been thoroughly explored by crystallographic studies. Structural analysis revealed that the anion⋯? and ?⋯? interactions along with intermolecular hydrogen bonding mutually cooperate to facilitate the assembling of the supramolecular framework. The ?⋯? and corresponding anion⋯? interactions have been investigated in the title carbene proligands despite their association with counter ions. The presence of the anion in the vicinity of the ?-system leads to the formation of anion⋯?/?⋯?/?⋯anion network for an inductive stabilization of the assemblies. To assess the dimensionality of the supramolecular framework consolidated by cooperative anion⋯?/?⋯? interactions and hydrogen bonding, different substituent effects in the carbene backbone have been considered to tune these interactions. These facts show that the supramolecular framework based on these cooperative weak forces may be robust enough for application in molecular recognition. The investigation of close intermolecular interactions between the molecules via Hirshfeld surface analyses is presented in order to reveal subtle differences and similarities in the crystal structures. The decomposition of the fingerprint plot area provides a percentage of each intermolecular interaction, allowing for a quantified analysis of close contacts within each crystal.

  9. Traditional and ion-pair halogen-bonded complexes between chlorine and bromine derivatives and a nitrogen-heterocyclic carbene.

    PubMed

    Donoso-Tauda, Oscar; Jaque, Pablo; Elguero, José; Alkorta, Ibon

    2014-10-01

    A theoretical study of the halogen-bonded complexes (A-X···C) formed between halogenated derivatives (A-X; A = F, Cl, Br, CN, CCH, CF3, CH3, H; and X = Cl, Br) and a nitrogen heterocyclic carbene, 1,3-dimethylimidazole-2-ylidene (MeIC) has been performed using MP2/aug'-cc-pVDZ level of theory. Two types of A-X:MeIC complexes, called here type-I and -II, were found and characterized. The first group is described by long C-X distances and small binding energies (8-54 kJ·mol(-1)). In general, these complexes show the traditional behavior of systems containing halogen-bonding interactions. The second type is characterized by short C-X distances and large binding energies (148-200 kJ·mol(-1)), and on the basis of the topological analysis of the electron density, they correspond to ion-pair halogen-bonded complexes. These complexes can be seen as the interaction between two charged fragments: A(-) and (+)[X-CIMe] with a high electrostatic contribution in the binding energy. The charge transfer between lone pair A(LP) to the ?* orbital of C-X bond is also identified as a significant stabilizing interaction in type-II complexes. PMID:25188812

  10. Physicochemical analysis of ruthenium(II) sensitizers of 1,2,3-triazole-derived mesoionic carbene and cyclometalating ligands.

    PubMed

    Sinn, Stephan; Schulze, Benjamin; Friebe, Christian; Brown, Douglas G; Jäger, Michael; Altunta?, Esra; Kübel, Joachim; Guntner, Oliver; Berlinguette, Curtis P; Dietzek, Benjamin; Schubert, Ulrich S

    2014-02-17

    A series of heteroleptic bis(tridentate) ruthenium(II) complexes bearing ligands featuring 1,2,3-triazolide and 1,2,3-triazolylidene units are presented. The synthesis of the C^N^N-coordinated ruthenium(II) triazolide complex is achieved by direct C-H activation, which is enabled by the use of a 1,5-disubstituted triazole. By postcomplexation alkylation, the ruthenium(II) 1,2,3-triazolide complex can be converted to the corresponding 1,2,3-triazolylidene complex. Additionally, a ruthenium(II) complex featuring a C^N^C-coordinating bis(1,2,3-triazolylidene)pyridine ligand is prepared via transmetalation from a silver(I) triazolylidene precursor. The electronic consequences of the carbanion and mesoionic carbene donors are studied both experimentally and computationally. The presented complexes exhibit a broad absorption in the visible region as well as long lifetimes of the charge-separated excited state suggesting their application in photoredox catalysis and photovoltaics. Testing of the dyes in a conventional dye-sensitized solar cell (DSSC) generates, however, only modest power conversion efficiencies (PCEs). PMID:24467434

  11. From the N-Heterocyclic Carbene-Catalyzed Conjugate Addition of Alcohols to the Controlled Polymerization of (Meth)acrylates.

    PubMed

    Ottou, Winnie Nzahou; Bourichon, Damien; Vignolle, Joan; Wirotius, Anne-Laure; Robert, Fredéric; Landais, Yannick; Sotiropoulos, Jean-Marc; Miqueu, Karinne; Taton, Daniel

    2015-06-22

    Among various N-heterocyclic carbenes (NHCs) tested, only 1,3-bis(tert-butyl)imidazol-2-ylidene (NHC(tBu) ) proved to selectively promote the catalytic conjugate addition of alcohols onto (meth)acrylate substrates. This rather rare example of NHC-catalyzed 1,4-addition of alcohols was investigated as a simple means to trigger the polymerization of both methyl methacrylate and methyl acrylate (MMA and MA, respectively). Well-defined ?-alkoxy poly(methyl (meth)acrylate) (PM(M)A) chains, the molar masses of which could be controlled by the initial [(meth)acrylate]0 /[ROH]0 molar ratio, were ultimately obtained in N,N-dimethylformamide at 25?°C. A hydroxyl-terminated poly(ethylene oxide) (PEO-OH) macro-initiator was also employed to directly access PEO-b-PMMA amphiphilic block copolymers. Investigations into the reaction mechanism by DFT calculations revealed the occurrence of two competitive concerted pathways, involving either the activation of the alcohol or that of the monomer by NHC(tBu) . PMID:26013759

  12. Metal complexes of a boron-dipyrromethene (BODIPY)-tagged N-heterocyclic carbene (NHC) as luminescent carbon monoxide chemodosimeters.

    PubMed

    Kos, Pavlo; Plenio, Herbert

    2015-01-12

    Several metal complexes with a boron dipyrromethene (BODIPY)-functionalized N-heterocyclic carbene (NHC) ligand 4 were synthesized. The fluorescence in [(4)(SIMes)RuCl2(ind)] complex is quenched (? = 0.003), it is weak in [(4)PdI2(Clpy)] (? = 0.033), and strong in [(4)AuI] (? = 0.70). The BODIPY-tagged complexes can experience pronounced changes in the brightness of the fluorophore upon ligand-exchange and ligand-dissociation reactions. Complexes [(4)MX(1,5-cyclooctadiene)] (M = Rh, Ir; X = Cl, I; ? = 0.008-0.016) are converted into strongly fluorescent complexes [(4)MX(CO)2] (? = 0.53-0.70) upon reaction with carbon monoxide. The unquenching of the Rh and Ir complexes appears to be a consequence of the decreased electron density at Rh or Ir in the carbonyl complexes. In contrast, the substitution of an iodo ligand in [(4)AuI] by an electron-rich thiolate decreases the brightness of the BODIPY fluorophore, rendering the BODIPY as a highly sensitive probe for changes in the coordination sphere of the transition metal. PMID:25487747

  13. Cationic gold(I) heteroleptic complexes bearing a pyrazole-derived N-heterocyclic carbene: syntheses, characterizations, and cytotoxic activities.

    PubMed

    Sivaram, Haresh; Tan, Jackie; Huynh, Han Vinh

    2013-09-14

    A series of cationic gold(I) heteroleptic complexes bearing the pyrazole-derived N-heterocyclic carbene (NHC) FPyr (1,2,3,4,6,7,8,9-octahydropyridazino[1,2-a]indazolin-11-ylidene), and either a 1,3-disubstituted benzimidazole-derived NHC of the type RR'-bimy (3: R = R' = CHPh2; 4: R = CHPh2, R' = (i)Pr; 5: R = R' = CH2Ph; 6: R = R' = (i)Bu; 7: R = R' = n-Pr; 8: R = R' = Et; 9: R = R' = 2-propenyl) or a non-NHC co-ligand L (10: L = PPh3; 11: L = P(OPh)3; 12: L = DMAP) (DMAP = 4-dimethylaminopyridine) have been synthesized from [AuCl(FPyr)] (1). Complexes 3-12 have been characterized using multinuclei NMR spectroscopies, ESI mass spectrometry, and elemental analysis. X-ray diffraction analyses have been performed on complexes 5, 6, and 9-11. To the best of our knowledge, 11 represents the first gold-NHC complex to bear the P(OPh)3 ligand. The cytotoxic activities of complexes 3-12 have been studied in vitro with the NCI-H1666 non-small cell lung cancer cell line. PMID:23860905

  14. Comproportionation of Cationic and Anionic Tungsten Complexes Having an N-Heterocyclic Carbene Ligand to Give the Isolable 17-Electron Tungsten Radical, CpW(CO)2(IMes)•

    SciTech Connect

    Roberts, John A.; Franz, James A.; van der Eide, Edwin F.; Walter, Eric D.; Petersen, Jeffrey L.; DuBois, Daniel L.; Bullock, R. Morris

    2011-09-21

    A series consisting of a tungsten anion, radical and cation, supported by the N-heterocyclic carbene IMes (1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) and spanning formal oxidation states W(0), W(I) and W(II), has been synthesized, isolated, and characterized. Reaction of the hydride CpW(CO)2(IMes)H with KH and 18 crown 6 gives the tungsten anion [CpW(CO)2(IMes)]-[K(18 crown 6)]+. The crystal structure of this complex shows that the K+ interacts not only with the oxygen atoms in the crown ether, but also with the carbonyl oxygens. The electrochemical oxidation of [CpW(CO)2(IMes)]- in acetonitrile is fully reversible (E½ = ?1.65 V vs Cp2Fe+•/0) at all scan rates, indicating that CpW(CO)2(IMes)• is a persistent radical. Hydride transfer from CpW(CO)2(IMes)H to Ph3C+PF6 affords [cis-CpW(CO)2(IMes)(MeCN)]+PF6 . Comproportionation of [CpW(CO)2(IMes)]- with [CpW(CO)2(IMes)(MeCN)]+ gives the 17-electron tungsten radical CpW(CO)2(IMes)•. This complex shows paramagnetically shifted resonances in 1H NMR spectra and has been characterized by IR spectroscopy, low-temperature EPR spectroscopy, and X-ray diffraction. CpW(CO)2(IMes)• is very stable with respect to disproportionation and dimerization. NMR studies of degenerate electron transfer between CpW(CO)2(IMes)• and [CpW(CO)2(IMes)]- are reported. DFT calculations were carried out on CpW(CO)2(IMes)H, as well as on related complexes bearing NHC ligands with N,N´ substituents Me [CpW(CO)2(IMe)H] or H [CpW(CO)2(IH)H] to compare to the experimentally studied IMes complexes with mesityl substituents. These calculations reveal W H homolytic bond dissociation energies (BDEs) to decrease with increasing steric bulk of the NHC ligand, from 67 for CpW(CO)2(IH)H to 64 for CpW(CO)2(IMe)H to 63 kcal/mol for CpW(CO)2(IMes)H. The calculated spin density at W for CpW(CO)2(IMes)• is 0.63. The W radicals CpW(CO)2(IMe)• and CpW(CO)2(IH)• are calculated to form weak W W bonds. The weakly bonded complexes [CpW(CO)2(IMe)]2 and [CpW(CO)2(IH)]2, are predicted to have W-W BDEs of 6 and 18 kcal/mol, respectively, and to dissociate readily to the W-centered radicals CpW(CO)2(IMe)• and CpW(CO)2(IH)•. This work was supported by the US Department of Energy Basic Energy Sciences' Chemical Sciences, Geosciences & Biosciences Division. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

  15. Magnetotelluric Data, Stable Distributions and Stable Regression

    NASA Astrophysics Data System (ADS)

    Chave, A. D.

    2013-12-01

    The author has noted for many years that the residuals from robust or bounded influence estimates of the magnetotelluric response function are systematically long tailed compared to a Gaussian or Rayleigh distribution. Consequently, the standard statistical model of a Gaussian core contaminated by a fraction of outlying data is not really valid. However, the typical result is an improvement on ordinary least squares, and has become standard in the electromagnetic induction community. A recent re-evaluation of the statistics of magnetotelluric response function estimation has shown that, in almost all cases, the residuals are alpha stable rather than Gaussian. Alpha stable distributions are characterized by four parameters: a shape parameter lying on (0, 2], a skewness parameter, a scale parameter and a location parameter, and cannot be expressed in closed form except for a few special cases. When the shape parameter is 2, the result is Gaussian, but when it is smaller the resulting distribution has infinite variance. Typical magnetotelluric residuals are alpha stable with a shape parameter lying between 1 and 2. This suggests that robust methods improve response function estimates by eliminating data corresponding to the largest stable residuals while leaving the bulk of the population alone. A better statistical approach is based on stable regression that directly accommodates the actual residual distribution without eliminating the most extreme ones. This paper will introduce such an algorithm, and illustrate its functionality with a variety of magnetotelluric data. Further work remains to produce a robust stable regression algorithm that will eliminate real outliers such as lightning strikes or instrument problems without affecting the bulk stable population. Stable distributions are intimately associated with fractional derivative physical processes. Since the Maxwell equations and the constitutive relations pertaining to the earth do not contain any fractional derivatives, the pervasive occurrence of stable residuals for magnetotelluric response function estimates must have an origin in the ionospheric and magnetospheric sources.

  16. Twisted stable homotopy theory

    E-print Network

    Douglas, Christopher L

    2005-01-01

    There are two natural interpretations of a twist of stable homotopy theory. The first interpretation of a twist is as a nontrivial bundle whose fibre is the stable homotopy category. This kind of radical global twist forms ...

  17. Bis(1,2,3-triazol-5-ylidenes) (i-bitz) as Stable 1,4-Bidentate Ligands Based on Mesoionic Carbenes (MICs)

    PubMed Central

    Guisado-Barrios, Gregorio; Bouffard, Jean; Donnadieu, Bruno

    2011-01-01

    Direct metalation of bis(1,2,3-triazolium) salts affords mononuclear rhodium(I) complexes, which feature a 1,4-bidentate bis(1,2,3-triazol-5-ylidene) (i-bitz) ligand. The topology of the ligand is similar to 2,2?-bipyridines (bpy) and their congeners, as well as bis(1,2,4-triazol-5-ylidenes) (bitz). As the former, but in contrast to the latter, the free i-bitz can be isolated, which paves the way for various applications. PMID:22096269

  18. Ligand Steric Contours to Understand the Effects of N-Heterocyclic Carbene Ligands on the Reversal of Regioselectivity in Ni-Catalyzed Reductive Couplings of Alkynes and Aldehydes

    PubMed Central

    Liu, Peng

    2011-01-01

    The regioselectivities of N-heterocyclic carbene (NHC) ligands in Ni-catalyzed alkyne–aldehyde reductive coupling reactions with silane reducing agents are investigated using density functional theory. Reversal of regioselectivities can be achieved by varying the steric bulkiness of the ligand. The steric influences of NHC ligands are highly anisotropic. The regioselectivity is primarily controlled by the steric hindrance at the region of the ligand close to the alkyne. Analysis of 2D contour maps of the NHC ligands indicates that the regioselectivities are directly affected by the shape and orientation of the N-substituents on the ligand. PMID:21506540

  19. Ru(II)-Catalyzed Mild [3+2] Carbocyclization with Aromatic N-H Ketimines and Internal Alkynes Using N-Heterocyclic Carbene (NHC) Ligands

    PubMed Central

    Zhang, Jing; Ugrinov, Angel

    2013-01-01

    A convenient and highly efficient synthesis of indenamines has been developed via ruthenium-catalyzed [3+2] carbocyclization under very mild conditions. A catalyst system of Ru(II) ?-allyl precursor and N-heterocyclic carbene (NHC) ligand promotes facile coupling between aromatic N–H ketimines with internal alkynes at mild temperatures, without added oxidants or other metal salts, and in non-polar solvents. A proposed mechanism involves imine-directed activation of aromatic C–H bond, alkyne insertion, and carbocyclization by intramolecular imine insertion into Ru–alkenyl linkages. PMID:23696055

  20. Anticancer Activity of Ag(I) N-Heterocyclic Carbene Complexes Derived from 4,5-Dichloro-1H-Imidazole

    PubMed Central

    Medvetz, Doug A.; Hindi, Khadijah M.; Panzner, Matthew J.; Ditto, Andrew J.; Yun, Yang H.; Youngs, Wiley J.

    2008-01-01

    A class of Ag(I) N-heterocyclic carbene silver complexes, 1–3, derived from 4,5-dichloro-1H-imidazole has been evaluated for their anticancer activity against the human cancer cell lines OVCAR-3 (ovarian), MB157 (breast), and Hela (cervical). Silver complexes 1–3 are active against the ovarian and breast cancer cell lines. A preliminary in vivo study shows 1 to be active against ovarian cancer in mice. The results obtained in these studies warrant further investigation of these compounds in vivo. PMID:18615197

  1. Synthesis of Well-Defined Copper "N"-Heterocyclic Carbene Complexes and Their Use as Catalysts for a "Click Reaction": A Multistep Experiment that Emphasizes the Role of Catalysis in Green Chemistry

    ERIC Educational Resources Information Center

    Ison, Elon A.; Ison, Ana

    2012-01-01

    A multistep experiment for an advanced synthesis lab course that incorporates topics in organic-inorganic synthesis and catalysis and highlights green chemistry principles was developed. Students synthesized two "N"-heterocyclic carbene ligands, used them to prepare two well-defined copper(I) complexes and subsequently utilized the complexes as…

  2. The ketimide ligand is not just an inert spectator: heteroallene insertion reactivity of an actinide-ketimide linkage in a thorium carbene amide ketimide complex.

    PubMed

    Lu, Erli; Lewis, William; Blake, Alexander J; Liddle, Stephen T

    2014-08-25

    The ketimide anion R2C=N(-) is an important class of chemically robust ligand that binds strongly to metal ions and is considered ideal for supporting reactive metal fragments due to its inert spectator nature; this contrasts with R2N(-) amides that exhibit a wide range of reactivities. Here, we report the synthesis and characterization of a rare example of an actinide ketimide complex [Th(BIPM(TMS)){N(SiMe3)2}(N=CPh2)] [2, BIPM(TMS)=C(PPh2NSiMe3)2]. Complex 2 contains Th=C(carbene), Th-N(amide) and Th-N(ketimide) linkages, thereby presenting the opportunity to probe the preferential reactivity of these linkages. Importantly, reactivity studies of 2 with unsaturated substrates shows that insertion reactions occur preferentially at the Th-N(ketimide) bond rather than at the Th=C(carbene) or Th-N(amide) bonds. This overturns the established view that metal-ketimide linkages are purely inert spectators. PMID:25044515

  3. C^C* cyclometalated platinum(ii) N-heterocyclic carbene complexes with a sterically demanding ?-diketonato ligand - synthesis, characterization and photophysical properties.

    PubMed

    Tenne, M; Metz, S; Wagenblast, G; Münster, Ingo; Strassner, T

    2015-04-29

    Neutral cyclometalated platinum(ii) N-heterocyclic carbene complexes [Pt(C^C*)(O^O)] with C^C* ligands based on 1-phenyl-1,2,4-triazol-5-ylidene and 4-phenyl-1,2,4-triazol-5-ylidene, as well as acetylacetonato (O^O = acac) and 1,3-bis(2,4,6-trimethylphenyl)propan-1,3-dionato (O^O = mesacac) ancillary ligands were synthesized and characterized. All complexes are emissive at room temperature in a poly(methyl methacrylate) (PMMA) matrix with emission maxima in the blue region of the spectrum. High quantum efficiencies and short decay times were observed for all complexes with mesacac ancillary ligands. The sterically demanding mesityl groups of the mesacac ligand effectively prevent molecular stacking. The emission behavior of these emitters is in general independent of the position of the nitrogen in the backbone of the N-heterocyclic carbene (NHC) unit and a variety of substituents in 4-position of the phenyl unit, meta to the cyclometalating bond. PMID:25884050

  4. INVERSE STABLE SUBORDINATORS

    PubMed Central

    MEERSCHAERT, MARK M.; STRAKA, PETER

    2013-01-01

    The inverse stable subordinator provides a probability model for time-fractional differential equations, and leads to explicit solution formulae. This paper reviews properties of the inverse stable subordinator, and applications to a variety of problems in mathematics and physics. Several different governing equations for the inverse stable subordinator have been proposed in the literature. This paper also shows how these equations can be reconciled. PMID:25045216

  5. The Stable Pairing Problem

    ERIC Educational Resources Information Center

    Greenwell, Raymond N.; Seabold, Daniel E.

    2014-01-01

    The Gale-Shapley stable marriage theorem is a fascinating piece of twentieth-century mathematics that has many practical applications--from labor markets to school admissions--yet is accessible to secondary school mathematics students. David Gale and Lloyd Shapley were both mathematicians and economists who published their work on the Stable

  6. Iridium(III) Hydrido N-Heterocyclic Carbene–Phosphine Complexes as Catalysts in Magnetization Transfer Reactions

    PubMed Central

    2013-01-01

    The hyperpolarization (HP) method signal amplification by reversible exchange (SABRE) uses para-hydrogen to sensitize substrate detection by NMR. The catalyst systems [Ir(H)2(IMes)(MeCN)2(R)]BF4 and [Ir(H)2(IMes)(py)2(R)]BF4 [py = pyridine; R = PCy3 or PPh3; IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene], which contain both an electron-donating N-heterocyclic carbene and a phosphine, are used here to catalyze SABRE. They react with acetonitrile and pyridine to produce [Ir(H)2(NCMe)(py)(IMes)(PPh3)]BF4 and [Ir(H)2(NCMe)(py)(IMes)(PCy3)]BF4, complexes that undergo ligand exchange on a time scale commensurate with observation of the SABRE effect, which is illustrated here by the observation of both pyridine and acetonitrile HP. In this study, the required symmetry breaking that underpins SABRE is provided for by the use of chemical inequivalence rather than the previously reported magnetic inequivalence. As a consequence, we show that the ligand sphere of the polarization transfer catalyst itself becomes hyperpolarized and hence that the high-sensitivity detection of a number of reaction intermediates is possible. These species include [Ir(H)2(NCMe)(py)(IMes)(PPh3)]BF4, [Ir(H)2(MeOH)(py)(IMes)(PPh3)]BF4, and [Ir(H)2(NCMe)(py)2(PPh3)]BF4. Studies are also described that employ the deuterium-labeled substrates CD3CN and C5D5N, and the labeled ligands P(C6D5)3 and IMes-d22, to demonstrate that dramatically improved levels of HP can be achieved as a consequence of reducing proton dilution and hence polarization wastage. By a combination of these studies with experiments in which the magnetic field experienced by the sample at the point of polarization transfer is varied, confirmation of the resonance assignments is achieved. Furthermore, when [Ir(H)2(pyridine-h5)(pyridine-d5)(IMes)(PPh3)]BF4 is examined, its hydride ligand signals are shown to become visible through para-hydrogen-induced polarization rather than SABRE. PMID:24215616

  7. Dissymmetric gold(I) N-heterocyclic carbene complexes: a key unexpected structural parameter for highly efficient catalysts in the addition of alcohols to internal alkynes.

    PubMed

    Bouhrara, Mohamed; Jeanneau, Erwan; Veyre, Laurent; Copéret, Christophe; Thieuleux, Chloé

    2011-03-28

    Gold(I) N-heterocyclic carbene complexes (Au-NHC) with symmetric (bis-benzyl, -propyl and -mesityl substituents) and dissymmetric (mesityl and alkyl--benzyl or propyl--substituents) NHC ligands were synthesized and tested as catalysts for the addition of methanol to 3-hexyne, as a representative internal alkyne. While symmetric ones--bis-alkyl (propyl or benzyl) or bis-mesityl systems--displayed low activity, dissymmetric Au-NHC systems with one alkyl (benzyl or propyl) and one mesityl groups on the NHC unit were unexpectedly highly active with rates and turnover numbers up to 294,000 h(-1) and 800,000 mol.mol(Au)(-1). PMID:21321729

  8. Novel [1,5] sigmatropic rearrangements of cyclohexadienones generated from Fischer carbene complexes. A new strategy for installing the C-20 angular ethyl group in Aspidospermidine alkaloids.

    PubMed

    Quinn, J F; Bos, M E; Wulff, W D

    1999-07-15

    [formula: see text] We report here the first examples of a [1,5] sigmatropic rearrangement in a 4a-alkyl-4a-hydrocarbazol-4-one to yield a 3-alkylcarbazol-4-one with a re-aromatized indole nucleus. The reaction of 1-methyl-3-substituted-indole-2-carbene complexes 1 with terminal alkynes yields 3,4a-dialkyl-1-methoxy-9-methylcarbazol-4-ones 2. These 4a-substituted carbazolones thermally rearrange to cleanly give the more highly aromatic 3,3-dialkyl-1-methoxy-9-methylcarbazol-4-ones 3. This reaction provides a convenient entry to the Aspidosperma family of alkaloids, which contain a 3,3-disubstituted carbazole nucleus. PMID:10822553

  9. Visible-Light Photoredox Catalysis: Selective Reduction of Carbon Dioxide to Carbon Monoxide by a Nickel N-Heterocyclic Carbene-Isoquinoline Complex

    SciTech Connect

    Thoi, VanSara; Kornienko, Nick; Margarit, C; Yang, Peidong; Chang, Christopher

    2013-06-07

    The solar-driven reduction of carbon dioxide to value-added chemical fuels is a longstanding challenge in the fields of catalysis, energy science, and green chemistry. In order to develop effective CO2 fixation, several key considerations must be balanced, including (1) catalyst selectivity for promoting CO2 reduction over competing hydrogen generation from proton reduction, (2) visible-light harvesting that matches the solar spectrum, and (3) the use of cheap and earth-abundant catalytic components. In this report, we present the synthesis and characterization of a new family of earth-abundant nickel complexes supported by N-heterocyclic carbene amine ligands that exhibit high selectivity and activity for the electrocatalytic and photocatalytic conversion of CO2 to CO. Systematic changes in the carbene and amine donors of the ligand have been surveyed, and [Ni(Prbimiq1)]2+ (1c, where Prbimiq1 = bis(3-(imidazolyl)isoquinolinyl)propane) emerges as a catalyst for electrochemical reduction of CO2 with the lowest cathodic onset potential (Ecat = 1.2 V vs SCE). Using this earth-abundant catalyst with Ir(ppy)3 (where ppy = 2-phenylpyridine) and an electron donor, we have developed a visible-light photoredox system for the catalytic conversion of CO2 to CO that proceeds with high selectivity and activity and achieves turnover numbers and turnover frequencies reaching 98,000 and 3.9 s1, respectively. Further studies reveal that the overall efficiency of this solar-to-fuel cycle may be limited by the formation of the active Ni catalyst and/or the chemical reduction of CO2 to CO at the reduced nickel center and provide a starting point for improved photoredox systems for sustainable carbon-neutral energy conversion.

  10. Stable coherent states

    E-print Network

    Zipfel, Antonia

    2015-01-01

    We analyze the stability under time evolution of complexifier coherent states (CCS) in one-dimensional mechanical systems. A system of coherent states is called stable if it evolves into another coherent state. It turns out that a system can only poses stable CCS if the classical evolution of the variable for a given complexifier C depends only on z itself and not on its complex conjugate. This condition is very restrictive in general so that only few systems exist that obey this condition. However, it is possible to access a wider class of models that in principle may allow for stable coherent states associated to certain regions in the phase space by introducing action-angle coordinates.

  11. Stable generalized complex structures

    E-print Network

    Cavalcanti, Gil R

    2015-01-01

    A stable generalized complex structure is one that is generically symplectic but degenerates along a real codimension two submanifold, where it defines a generalized Calabi-Yau structure. We introduce a Lie algebroid which allows us to view such structures as symplectic forms. This allows us to construct new examples of stable structures, and also to define period maps for their deformations in which the background three-form flux is either fixed or not, proving the unobstructedness of both deformation problems. We then use the same tools to establish local normal forms for the degeneracy locus and for Lagrangian branes. Applying our normal forms to the four-dimensional case, we prove that any compact stable generalized complex 4-manifold has a symplectic completion, in the sense that it can be modified near its degeneracy locus to produce a compact symplectic 4-manifold.

  12. Stable generalized complex structures

    E-print Network

    Gil R. Cavalcanti; Marco Gualtieri

    2015-03-21

    A stable generalized complex structure is one that is generically symplectic but degenerates along a real codimension two submanifold, where it defines a generalized Calabi-Yau structure. We introduce a Lie algebroid which allows us to view such structures as symplectic forms. This allows us to construct new examples of stable structures, and also to define period maps for their deformations in which the background three-form flux is either fixed or not, proving the unobstructedness of both deformation problems. We then use the same tools to establish local normal forms for the degeneracy locus and for Lagrangian branes. Applying our normal forms to the four-dimensional case, we prove that any compact stable generalized complex 4-manifold has a symplectic completion, in the sense that it can be modified near its degeneracy locus to produce a compact symplectic 4-manifold.

  13. Bis-N-heterocyclic carbene (NHC) stabilized ?6-arene iron(0) complexes: synthesis, structure, reactivity, and catalytic activity.

    PubMed

    Blom, Burgert; Tan, Gengwen; Enthaler, Stephan; Inoue, Shigeyoshi; Epping, Jan Dirk; Driess, Matthias

    2013-12-01

    Reaction of FeCl2 with the chelating bis-N-heterocyclic carbene (NHC) bis-(N-Dipp-imidazole-2-ylidene)methylene (abbreviated {((Dipp)C:)2CH2}) (Dipp = 2,6-di-isopropylphenyl) affords the complex [FeCl2{((Dipp)C:)2CH2}] (1) in high yield. Reduction of complex 1 with excess KC8 with a 10-fold molar excess of PMe3 affords the Fe(II) complex [FeH{((Dipp)C:)2CH2}(PMe3)(?(2)-PMe2CH2)] (2) as a mixture of three stereoisomers. Complex 2, the first example of any iron(II) complex bearing mutually an NHC and PMe3 ligand, is likely obtained from the in situ, reductively generated 16 VE Fe(0) complex, [Fe{((Dipp)C:)2CH2}(PMe3)2] (2'), following intramolecular C-H activation of one of the phosphorus-bound CH3 groups. Complex 2 is unstable in aromatic solvents and forms, via a novel synthetic transformation involving intramolecular reductive elimination and concomitant PMe3 elimination, the Fe (0) arene complex [Fe{((Dipp)C:)2CH2}(?(6)-C6D6)] (4-d6) in C6D6. Complex 4-d6 represents the first example of an NHC stabilized iron (0) arene complex. The transformation from 2 to 4-d6 can be accelerated at higher temperature and at 60 °C forms immediately. Alternatively, the reduction of 1 in the presence of toluene or benzene affords the complexes [Fe{((Dipp)C:)2CH2}(?(6)-C7H8)] (3) and [Fe{((Dipp)C:)2CH2}(?(6)-C6H6)] (4), selectively and in good yields. DFT calculations characterizing the bonding situation in 3 and 4 reveal similar energies of the HOMO and LUMO orbitals, with the LUMO orbital of both complexes located on the Dipp rings of the bis-NHC. The HOMO orbital reflects a ?-back-bonding interaction between the Fe(0) center and the chelating NHC ligand, while the HOMO-1 is associated with the arene interaction with the Fe(0) site. The calculations do not suggest any noninnocence of the coordinated arene in either complex. Moreover, the (57)Fe Mössbauer spectrum of 4 at 80K exhibits parameters (? = 0.43 mm·s(-1); ?EQ = 1.37 mm·s(-1)) which are consistent with a five-coordinate Fe(0) system, rendering 3 and 4 the first examples of well-defined authentic Fe(0)-?(6)-arene complexes of the type [Fe(?(6)-arene)L2] (L = ?(1 or 2) neutral ligand, mono or bidentate). Some reactivitiy studies of 3 are also reported: The reaction of 3 with excess CO selectively yields the five-coordinate piano-stool complex [Fe{((Dipp)C:)2CH2}(CO)3] (6) in near quantitative yields, while the reaction of complex 3 with C6D6 under heating affords by toluene elimination 4-d6. The catalytic ability of 4 was also investigated with respect to amide reduction to amines, for a variety of substrates using Ph2SiH2 as a hydride source. In all cases good to excellent yields to the corresponding amines were obtained. The use of 4 as a precatalyst represents the first example of a well-defined Fe(0) complex to effect this catalytic process. PMID:24195449

  14. Stable isotope studies

    SciTech Connect

    Ishida, T.

    1992-01-01

    The research has been in four general areas: (1) correlation of isotope effects with molecular forces and molecular structures, (2) correlation of zero-point energy and its isotope effects with molecular structure and molecular forces, (3) vapor pressure isotope effects, and (4) fractionation of stable isotopes. 73 refs, 38 figs, 29 tabs.

  15. Stable but responsive cloth

    Microsoft Academic Search

    Kwang-Jin Choi; Hyeong-Seok Ko

    2002-01-01

    We present a semi-implicit cloth simulation technique that is very stable yet also responsive. The stability of the technique allows the use of a large fixed time step when simulating all types of fabrics and character motions. The animations generated using this technique are strikingly realistic. Wrinkles form and disappear in a quite natural way, which is the feature that

  16. Stable Fluids Alias wavefront

    E-print Network

    Toronto, University of

    Stable Fluids Jos Stam Alias wavefront Abstract Building animation tools for fluid-like motions-based models for fluid flow can greatly assist in creating such tools. Physical models, unlike key frame or pro- cedural based techniques, permit an animator to almost effortlessly create interesting, swirling fluid

  17. Stable models and circumscription

    Microsoft Academic Search

    Paolo Ferraris; Joohyung Lee; Vladimir Lifschitz

    2011-01-01

    The concept of a stable model provided a declarative semantics for Prolog programs with negation as failure and became a starting point for the development of answer set programming. In this paper we propose a new definition of that concept, which covers many constructs used in answer set programming and, unlike the original definition, refers neither to grounding nor to

  18. Stable Models and Circumscription

    Microsoft Academic Search

    Paolo Ferraris; Joohyung Lee; Vladimir Lifschitz

    2007-01-01

    sThe definition of a stable model has provided a declarative semantics for Prolog programs with negation as failure and has led to the development of answer set programming. In this paper we propose a new definition of that concept, which covers many constructs used in answer set programming (including disjunctive rules, choice rules and conditional literals) and, unlike the original

  19. Stable glow discharge detector

    DOEpatents

    Koo, Jackson C.; Yu, Conrad M.

    2004-05-18

    A highly sensitive electronic ion cell for the measurement of trace elements in He carrier gas which involves glow discharge. A constant wave (CW) stable glow discharge detector which is controlled through a biased resistor, can detect the change of electron density caused by impurities in the He carrier gas by many orders of magnitude larger than that caused by direct ionization or electron capture. The stable glow discharge detector utilizes a floating pseudo-electrode to form a probe in or near the plasma and a solid rod electrode. By using this probe, the large variation of electron density due to trace amounts of impurities can be directly measured. The solid rod electrode provides greater stability and thus easier alignment.

  20. Bi-stable optical actuator

    DOEpatents

    Holdener, Fred R. (Tracy, CA); Boyd, Robert D. (Livermore, CA)

    2000-01-01

    The present invention is a bi-stable optical actuator device that is depowered in both stable positions. A bearing is used to transfer motion and smoothly transition from one state to another. The optical actuator device may be maintained in a stable position either by gravity or a restraining device.

  1. Colorado Plateau Stable Isotope Laboratory

    NSDL National Science Digital Library

    Colorado Plateau Stable Isotope Laboratory (CPSIL)

    This website, hosted by Northern Arizona University, describes stable isotopes. The site defines stable isotopes and how to measure them, and lists their research applications. Many of the advances in ecology and environmental sciences in the past decade have relied on stable isotopes.

  2. Copper- and copper–N-heterocyclic carbene-catalyzed C?H activating carboxylation of terminal alkynes with CO2 at ambient conditions

    PubMed Central

    Yu, Dingyi; Zhang, Yugen

    2010-01-01

    The use of carbon dioxide as a renewable and environmentally friendly source of carbon in organic synthesis is a highly attractive approach, but its real world applications remain a great challenge. The major obstacles for commercialization of most current protocols are their low catalytic performances, harsh reaction conditions, and limited substrate scope. It is important to develop new reactions and new protocols for CO2 transformations at mild conditions and in cost-efficient ways. Herein, a copper-catalyzed and copper–N-heterocyclic carbene-cocatalyzed transformation of CO2 to carboxylic acids via C?H bond activation of terminal alkynes with or without base additives is reported. Various propiolic acids were synthesized in good to excellent yields under ambient conditions without consumption of any organometallic or organic reagent additives. This system has a wide scope of substrates and functional group tolerances and provides a powerful tool for the synthesis of highly functionalized propiolic acids. This catalytic system is a simple and economically viable protocol with great potential in practical applications. PMID:21059950

  3. The first example of a two-coordinated Au(I) atom bonded to an Fe(II) atom and an N-heterocyclic carbene (NHC) ligand.

    PubMed

    Bechtoldt, Alexander; Lerner, Hans Wolfram; Bolte, Michael

    2015-06-01

    The aurophilicity exhibited by Au(I) complexes depends strongly on the nature of the supporting ligands present and the length of the Au-element (Au-E) bond may be used as a measure of the donor-acceptor properties of the coordinated ligands. A binuclear iron-gold complex, [1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene-2?C(2)]dicarbonyl-1?(2)C-(1?(5)-cyclopentadienyl)gold(I)iron(II)(Au-Fe) benzene trisolvate, [AuFe(C5H5)(C27H36N2)(CO)2]·3C6H6, was prepared by reaction of K[CpFe(CO)2] (Cp is cyclopentadienyl) with (NHC)AuCl [NHC = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene]. In addition to the binuclear complex, the asymmetric unit contains three benzene solvent molecules. This is the first example of a two-coordinated Au atom bonded to an Fe and a C atom of an N-heterocyclic carbene. PMID:26044324

  4. N-heterocyclic carbene-assisted, bis(phosphine)nickel-catalyzed cross-couplings of diarylborinic acids with aryl chlorides, tosylates, and sulfamates.

    PubMed

    Ke, Haihua; Chen, Xiaofeng; Zou, Gang

    2014-08-01

    Efficient bis(phosphine)nickel-catalyzed cross-couplings of diarylborinic acids with aryl chlorides, tosylates, and sulfamates have been effected with an assistance of N-heterocyclic carbene (NHC) generated in situ from N,N'-dialkylimidazoliums, e.g., N-butyl-N'-methylimidazolium bromide ([Bmim]Br), in toluene using K3PO4·3H2O as base. In contrast to bis(NHC)nickel-catalyzed conventional Suzuki coupling of arylboronic acids, mono(NHC)bis(phosphine)nickel species generated in situ from Ni(PPh3)2Cl2/[Bmim]Br displayed high catalytic activities in the cross-couplings of diarylborinic acids. The structural influences from diarylborinic acids were found to be rather small, while electronic factors from aryl chlorides, tosylates, and sulfamates affected the couplings remarkably. The couplings of electronically activated aryl chlorides, tosylates, and sulfamates could be efficiently effected with 1.5 mol % NiCl2(PPh3)2/[Bmim]Br as catalyst precursor to give the biaryl products in excellent yields, while 3-5 mol % loadings had to be used for the couplings of non- and deactivated ones. A small ortho-substitutent on the aromatic ring of aryl chlorides, tosylates, and sulfamates was tolerable. Applicability of the nickel-catalyzed cross-couplings in practical synthesis of fine chemicals has been demonstrated in process development for a third-generation topical retinoid, Adapalene. PMID:25025343

  5. Stepwise strategy to cyclometallated Pt(II) complexes with N-heterocyclic carbene ligands: a luminescence study on new ?-diketonate complexes.

    PubMed

    Fuertes, Sara; García, Hector; Perálvarez, Mariano; Hertog, Wim; Carreras, Josep; Sicilia, Violeta

    2015-01-19

    The imidazolium salt 3-methyl-1-(naphthalen-2-yl)-1H-imidazolium iodide (2) has been treated with silver(I) oxide and [{Pt(?-Cl)(?(3)-2-Me-C3H4)}2] (?(3)-2-Me-C3H4 = ?(3)-2-methylallyl) to give the intermediate N-heterocyclic carbene complex [PtCl(?(3)-2-Me-C3H4)(HCC*-?C*)] (3) (HCC*-?C* = 3-methyl-1-(naphthalen-2-yl)-1H-imidazol-2-ylidene). Compound 3 undergoes regiospecific cyclometallation at the naphthyl ring of the NHC ligand to give the five-membered platinacycle compound [{Pt(?-Cl)(CC*)}2] (4). Chlorine abstraction from 4 with ?-diketonate Tl derivatives rendered the corresponding neutral compounds [Pt(CC*)(L-O,O')] {L = acac (HL = acetylacetone) 5, phacac (HL = 1,3-diphenyl-1,3-propanedione) 6, hfacac (HL = hexafluoroacetylacetone) 7}. All of the compounds (3-7) were fully characterized by standard spectroscopic and analytical methods. X-ray diffraction studies were performed on 5-7, revealing short Pt-Pt and ?-? interactions in the solid-state structure. The influence of the R-substituents of the ?-diketonate ligand on the photophysical properties and the use of the most efficient emitter, 5, as phosphor converter has also been studied. PMID:25412763

  6. Ru(II) , Os(II) , and Ir(III) Complexes with Chelating Pyridyl-Mesoionic Carbene Ligands: Structural Characterization and Applications in Transfer Hydrogenation Catalysis.

    PubMed

    Bolje, Aljoša; Hohloch, Stephan; van der Meer, Margarethe; Košmrlj, Janez; Sarkar, Biprajit

    2015-04-27

    Chelating ligands with one pyridine donor and one mesoionic carbene donor are fast establishing themselves as privileged ligands in homogeneous catalysis. The synthesis of several new Ir(III) -Cp*- and Os(II) -Cym complexes (Cp*=pentamethylcyclopentadienyl, Cym=p-cymene=4-isopropyl-toluene) derived from chelating pyridyltriazolylidenes where the additional pyridine donor was incorporated via the azide part of the triazole is presented. Furthermore, different 4-substituted phenylacetylene building blocks have been used to introduce electronic fine-tuning in the ligands. The ligands thus can be generally described as 4-(4-R-phenyl)-3-methyl-1-(pyridin-2-yl)-1H-1,2,3-triazol-5-ylidene (with R being H (L(1) ), Me (L(2) ), OMe (L(3) ), CN (L(4) ), CF3 (L(5) ), Br (L(6) ) or NO2 (L(7) )). The corresponding complexes (Ir-1 to Ir-7 and Os-1 to Os-7) were characterized by standard spectroscopic methods, and the expected three-legged, piano-stool type coordination was unambiguously confirmed by X-ray diffraction analysis of selected compounds. Together with Ru(II) analogues previously reported by us, a total of 21 complexes were tested as (pre)catalysts for the transfer hydrogenation of carbonyl groups, showing a remarkable reactivity even at very low catalyst loadings. The electronic effects of the ligands as well as different substrates were investigated. Some mechanistic elucidations are also presented. PMID:25752929

  7. Marginally Stable Nuclear Burning

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod E.; Altamirano, D.

    2012-01-01

    Thermonuclear X-ray bursts result from unstable nuclear burning of the material accreted on neutron stars in some low mass X-ray binaries (LMXBs). Theory predicts that close to the boundary of stability oscillatory burning can occur. This marginally stable regime has so far been identified in only a small number of sources. We present Rossi X-ray Timing Explorer (RXTE) observations of the bursting, high- inclination LMXB 4U 1323-619 that reveal for the first time in this source the signature of marginally stable burning. The source was observed during two successive RXTE orbits for approximately 5 ksec beginning at 10:14:01 UTC on March 28, 2011. Significant mHz quasi- periodic oscillations (QPO) at a frequency of 8.1 mHz are detected for approximately 1600 s from the beginning of the observation until the occurrence of a thermonuclear X-ray burst at 10:42:22 UTC. The mHz oscillations are not detected following the X-ray burst. The average fractional rms amplitude of the mHz QPOs is 6.4% (3 - 20 keV), and the amplitude increases to about 8% below 10 keV.This phenomenology is strikingly similar to that seen in the LMXB 4U 1636-53. Indeed, the frequency of the mHz QPOs in 4U 1323-619 prior to the X-ray burst is very similar to the transition frequency between mHz QPO and bursts found in 4U 1636-53 by Altamirano et al. (2008). These results strongly suggest that the observed QPOs in 4U 1323-619 are, like those in 4U 1636-53, due to marginally stable nuclear burning. We also explore the dependence of the energy spectrum on the oscillation phase, and we place the present observations within the context of the spectral evolution of the accretion-powered flux from the source.

  8. Stable Superstring Relics

    E-print Network

    Sanghyeon Chang; Claudio Coriano; Alon E. Faraggi

    1996-05-15

    We investigate the cosmological constraints on exotic stable matter states which arise in realistic free fermionic superstring models. These states appear in the superstring models due to a ``Wilson--line'' breaking of the unifying non--Abelian gauge symmetry. In the models that we consider the unifying $SO(10)$ gauge symmetry is broken at the string level to $SO(6)\\times SO(4)$, $SU(5)\\times U(1)$ or $SU(3)\\times SU(2)\\times U(1)^2$. The exotic matter states are classified according to the patterns of the $SO(10)$ symmetry breaking. In $SO(6)\\times SO(4)$ and $SU(5)\\times U(1)$ type models one obtains fractionally charged states with $Q_{\\rm e.m.}=\\pm1/2$. In $SU(3)\\times SU(2)\\times U(1)^2$ type models one also obtains states with the regular charges under the Standard Model gauge group but with ``fractional'' charges under the $U(1)_{Z^\\prime}$ symmetry. These states include down--like color triplets and electroweak doublets, as well as states which are Standard Model singlets. By analyzing the renormalizable and nonrenormalizable terms of the superpotential in a specific superstring model, we show that these exotic states can be stable. We investigate the cosmological constraints on the masses and relic density of the exotic states. We propose that, while the abundance and the masses of the fractionally charged states are highly constrained, the Standard Model -- like states, and in particular the Standard Model singlet, are good dark matter candidates.

  9. Stable string bit models

    NASA Astrophysics Data System (ADS)

    Sun, Songge; Thorn, Charles B.

    2014-05-01

    In string bit models, the superstring emerges as a very long chain of "bits," in which s fermionic degrees of freedom contribute positively to the ground state energy in a way to exactly cancel the destabilizing negative contributions of d=s bosonic degrees of freedom. We propose that the physics of string formation be studied nonperturbatively in the class of string bit models in which s>d, so that a long chain is stable, in contrast to the marginally stable (s=d=8) superstring chain. We focus on the simplest of these models with s=1 and d=0, in which the string bits live in zero space dimensions. The string bit creation operators are N×N matrices. We choose a Hamiltonian such that the large N limit produces a string moving in one space dimension, with excitations corresponding to one Grassmann light-cone world sheet field (s=1) and no bosonic world sheet field (d=0). We study this model at finite N to assess the role of the large N limit in the emergence of the spatial dimension. Our results suggest that stringlike states with large bit number M may not exist for N?(M-1)/2. If this is correct, one can have finite chains of string bits, but not a continuous string, at finite N. Only for extremely large N can such chains behave approximately like a continuous string, in which case there will also be the (approximate) emergence of a new spatial dimension. In string bit models designed to produce a critical superstring at N=?, we can then expect only approximate Lorentz invariance at finite N, with violations of order 1/N2.

  10. Effectively Stable Dark Matter

    E-print Network

    Cheung, Clifford

    2015-01-01

    We study dark matter (DM) which is cosmologically long-lived because of standard model (SM) symmetries. In these models an approximate stabilizing symmetry emerges accidentally, in analogy with baryon and lepton number in the renormalizable SM. Adopting an effective theory approach, we classify DM models according to representations of $SU(3)_C\\times SU(2)_L\\times U(1)_Y \\times U(1)_B\\times U(1)_L$, allowing for all operators permitted by symmetry, with weak scale DM and a cutoff at or below the Planck scale. We identify representations containing a neutral long-lived state, thus excluding dimension four and five operators that mediate dangerously prompt DM decay into SM particles. The DM relic abundance is obtained via thermal freeze-out or, since effectively stable DM often carries baryon or lepton number, asymmetry sharing through the very operators that induce eventual DM decay. We also incorporate baryon and lepton number violation with a spurion that parameterizes hard breaking by arbitrary units. Howev...

  11. Do stable atmospheric layers exist?

    NASA Astrophysics Data System (ADS)

    Lovejoy, S.; Tuck, A. F.; Hovde, S. J.; Schertzer, D.

    2008-01-01

    The notion of stable atmospheric layers is a classical idealization used for understanding atmospheric dynamics and thermodynamics. Using state of the art drop sonde data and using conditional, dynamical and convective stability criteria we show that apparently stable layers are typically composed of a hierarchy of unstable layers themselves with embedded stable sublayers, and unstable sub-sub layers etc. i.e. in a Russian Matryoshka doll-like fractal hierarchy. We therefore argue that the notion of stable atmospheric layers is untenable and must be replaced by modern scaling notions.

  12. Stable Morphisms to Singular Schemes and Relative Stable Morphisms

    Microsoft Academic Search

    Jun Li

    2001-01-01

    Let W\\/C be a degeneration of smooth varieties so that the special fiber has normal crossing singularity. In this paper, we first construct the stack of expanded degenerations of W. We then construct the moduli space of stable morphisms to this stack, which provides a degeneration of the moduli spaces of stable morphisms associated to W\\/C. Using a similar technique,

  13. Bis-N-Heterocyclic Carbene Palladium(IV) Tetrachloride Complexes: Synthesis, Reactivity and Mechanisms of Direct Chlorinations and Oxidations of Organic Substrates

    PubMed Central

    McCall, A. Scott; Wang, Hongwang; Desper, John M.; Kraft, Stefan

    2014-01-01

    This paper describes the preparation and isolation of novel octahedral CH2-bridged bis-(N-heterocyclic carbene)palladium(IV) tetrachlorides of the general formula LPdIVCl4 [L = (NHC)CH2(NHC)] from LPdIICl2 and Cl2. In intermolecular, non-chelation controlled transformations LPdIVCl4 reacted with alkenes and alkynes to 1,2-dichlorination adducts. Aromatic, benzylic, and aliphatic CH-bonds were converted into C-Cl bonds. Detailed mechanistic investigations in the dichlorinations of alkenes were conducted on the 18VE PdIV-complex. Positive solvent effects as well as kinetic measurements probing the impact of cyclohexene- and chloride concentrations on the rate of alkene chlorination, support a PdIV-Cl ionization in the first step. Product stereochemistry and product distributions from various alkenes also support Cl+-transfer from the pentacoordinated PdIV-intermediate LPdIVCl3+ to olefins. 1-hexene/3-hexene competition experiments rule out both the formation of ?-complexes along the reaction coordinate as well as in situ generated Cl2 from a reductive elimination process. Instead, a ligand-mediated direct Cl+-transfer from LPdIVCl3+ to the ?-system is likely to occur. Similarly, C-H bond chlorinations proceed via an electrophilic process with in situ formed LPdIVCl3+. The presence of a large excess of added Cl? slows down cyclohexene chlorination while the presence of stoichiometric amounts of chloride accelerates both PdIV-Cl ionization and Cl+-transfer from LPdIVCl3+. 1H NMR titrations, T1 relaxation time measurements, binding isotherms and Job plot analysis point to the formation of a trifurcated Cl?…H-C bond in the NHC-ligand periphery as a supramolecular cause for the accelerated chemical events involving the metal center. PMID:21247150

  14. Reactivity of coordinatively unsaturated bis(N-heterocyclic carbene) Pt(II) complexes toward H(2). Crystal structure of a 14-electron Pt(II) hydride complex.

    PubMed

    Rivada-Wheelaghan, Orestes; Roselló-Merino, Marta; Ortuño, Manuel A; Vidossich, Pietro; Gutiérrez-Puebla, Enrique; Lledós, Agustí; Conejero, Salvador

    2014-04-21

    The reactivity toward H2 of coordinatively unsaturated Pt(II) complexes, stabilized by N-heterocyclic carbene (NHC) ligands, is herein analyzed. The cationic platinum complexes [Pt(NHC')(NHC)](+) (where NHC' stands for a cyclometalated NHC ligand) react very fast with H2 at room temperature, leading to hydrogenolysis of the Pt-CH2 bond and concomitant formation of hydride derivatives [PtH(NHC)2](+) or hydrido-dihydrogen complexes [PtH(H2)(NHC)2](+). The latter species release H2 when these compounds are subjected to vacuum. The X-ray structure of complex [PtH(IPr)2][SbF6] revealed its unsaturated nature, exhibiting a true T-shaped structure without stabilization by agostic interactions. Density functional theory calculations indicate that the binding and reaction of H2 in complexes [PtH(H2)(NHC)2](+) is more favored for derivatives bearing aryl-substituted NHCs (IPr, 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene and IMes = 1,3-dimesityl-1,3-dihydro-2H-imidazol-2-ylidene) than for those containing tert-butyl groups (I(t)Bu). This outcome is related to the higher close-range steric effects of the I(t)Bu ligands. Accordingly, H/D exchange reactions between hydrides [PtH(NHC)2](+) and D2 take place considerably faster for IPr and IMes* derivatives than for I(t)Bu ones. The reaction mechanisms for both H2 addition and H/D exchange processes depend on the nature of the NHC ligand, operating through oxidative addition transition states in the case of IPr and IMes* or by a ?-complex assisted-metathesis mechanism in the case of I(t)Bu. PMID:24716606

  15. Stable isotope laser spectroscopy

    NASA Technical Reports Server (NTRS)

    Becker, J. F.; Yaldaei, Ramil; Mckay, Christopher P.

    1989-01-01

    Recent advances in semiconductor laser technology have produced a reliable lightweight device ideally suited for a spacecraft high resolution molecular spectrometer. Lead-salt tunable diode lasers (TDL) emit in several spectral modes, each with a very narrow linewidth of -0.0003/cm. This spectral resolution is much narrower than typical Doppler broadened molecular linewidths in the mid-IR range. Thus it is possible to detect individual rotational lines within the vibrational band and measure their intensity, which can be used to determine gas concentration. The narrow spectral lines of any impurity gas tend to lie between the narrow lines of the gas of interest. This represents a major advantage over the accepted gas chromatograph mass spectrometer (GCMS) technique for measuring gas concentrations and isotope ratios. The careful and extensive gas purification procedures required to remove impurities for reliable GCMS measurements will not be required for an IR laser gas analysis. The infrared laser gas analysis technique is being developed to measure stable isotopic ratios of gases such as CO2, CH4, N2O, and NH3. This will eventually lead to development of instruments capable of in situ istopic measurements on planets such as Mars. The carbon (C-12, C-13) isotope ratio is indicative of the type of carbon fixation mechanisms (e.g., photosynthesis, respiration) in operation on a planet, while the nitrogen (N-14, N-15) isotope ratio can probably be used to date nitrogen-bearing Martian samples. The absorbance ratio of two adjacent lines of CO2 in the 2300/cm (4.3 micron) region of the spectrum was measured. The precision of the measurement is presently better than 1 percent and significant improvement is anticipated as rapid sweep-integration techniques and computer controlled data acquistion capabilities are incorporated.

  16. Room temperature ring expansion of N-heterocyclic carbenes and b?b bond cleavage of diboron(4) compounds.

    PubMed

    Pietsch, Sabrina; Paul, Ursula; Cade, Ian A; Ingleson, Michael J; Radius, Udo; Marder, Todd B

    2015-06-15

    We report the isolation and detailed structural characterization, by solid-state and solution NMR spectroscopy, of the neutral mono- and bis-NHC adducts of bis(catecholato)diboron (B2 cat2 ). The bis-NHC adduct undergoes thermally induced rearrangement, forming a six-membered -B?C?N?C?C-N-heterocyclic ring via C?N bond cleavage and ring expansion of the NHC, whereas the mono-NHC adduct is stable. Bis(neopentylglycolato)diboron (B2 neop2 ) is much more reactive than B2 cat2 giving a ring expanded product at room temperature, demonstrating that ring expansion of NHCs can be a very facile process with significant implications for their use in catalysis. PMID:25960171

  17. Stable Black Families. Final Report.

    ERIC Educational Resources Information Center

    Gary, Lawrence E.; And Others

    This document is the final report of a study conducted to determine what factors contribute to strong Black family life and how these strong families solve problems, in order to add to the knowledge base on stable families so as to enhance practical intervention with families in need, and to identify models of self-help strategies used by stable

  18. Bayesian Inference for Stable Distributions

    Microsoft Academic Search

    D. J. Buckle

    1995-01-01

    Very little work on stable distribution parameter estimation and inference appears in the literature due to the nonexistence of the probability density function. This has led in particular to a dearth of Bayesian work in this area. But Bayesian computation via Markov chain Monte Carlo allows us to sample from the distribution of the parameters of the stable distributions, by

  19. Tampering with a Stable Process.

    ERIC Educational Resources Information Center

    Krehbiel, Timothy C.

    1994-01-01

    Presents a variation of Deming's funnel experiment to illustrate how a stable process operates and how tampering with a stable process leads to increased variability and less desirable results. The goal of the activity is to minimize product variation around the target value. Includes student handout. (Author/MKR)

  20. Stable Models and Difference Logic

    Microsoft Academic Search

    Ilkka Niemel

    The paper studies the relationship between logic programs with the stable model semantics and difference logic recently considered in the Satisfiability Modulo Theories framework. Characterizations of stable models in terms of level rankings are developed building on simple linear integer constraints allowed in difference logic. Based on a characterization with level rankings a translation is devised which maps a normal

  1. STABLE ISOTOPES IN PLANT ECOLOGY

    Microsoft Academic Search

    Todd E. Dawson; Stefania Mambelli; Agneta H. Plamboeck; Pamela H. Templer; Kevin P. Tu

    2002-01-01

    ? Abstract The use of stable isotope techniques in plant ecological research has grown steadily during the past two decades. This trend will continue as investigators realize that stable isotopes can serve as valuable nonradioactive tracers and nondestruc- tive integrators of how plants today and in the past have interacted with and responded to their abiotic and biotic environments. At

  2. Stable PDE Fluids Adrien Treuille

    E-print Network

    Treuille, Adrien

    Stable PDE Fluids Adrien Treuille Saturday, October 23, 2010 #12;Overview ·Last Week's Question: Advection ·Fluid Particles (recap) ·From Particles to PDEs ·The Navier Stokes Equations ·Stable Fluids Implementation ·Questions Saturday, October 23, 2010 #12;Overview ·Last Week's Question: Advection ·Fluid

  3. Stable Spheromaks with Profile Control

    SciTech Connect

    Fowler, T K; Jayakumar, R

    2008-01-29

    A spheromak equilibrium with zero edge current is shown to be stable to both ideal MHD and tearing modes that normally produce Taylor relaxation in gun-injected spheromaks. This stable equilibrium differs from the stable Taylor state in that the current density j falls to zero at the wall. Estimates indicate that this current profile could be sustained by non-inductive current drive at acceptable power levels. Stability is determined using the NIMROD code for linear stability analysis. Non-linear NIMROD calculations with non-inductive current drive could point the way to improved fusion reactors.

  4. Stable plastid transformation of petunia.

    PubMed

    Avila, Elena Martin; Day, Anil

    2014-01-01

    Petunia hybrida is a commercial ornamental plant and is also an important model species for genetic analysis and transgenic research. Here we describe the steps required to isolate stable plastid transformants in P. hybrida using the commercial Pink Wave cultivar. Wave cultivars are popular spreading Petunias sold as ground cover and potted plants. Transgenes introduced into P. hybrida plastids exhibit stable expression over many generations. The development of plastid transformation in P. hybrida provides an enabling technology to bring the benefits of plastid engineering, including maternal inheritance and stable expression of performance-enhancing trait genes, to the important floriculture and horticulture industries. PMID:24599860

  5. Organocatalytic conjugate-addition polymerization of linear and cyclic acrylic monomers by N-heterocyclic carbenes: mechanisms of chain initiation, propagation, and termination.

    PubMed

    Zhang, Yuetao; Schmitt, Meghan; Falivene, Laura; Caporaso, Lucia; Cavallo, Luigi; Chen, Eugene Y-X

    2013-11-27

    This contribution presents a full account of experimental and theoretical/computational investigations into the mechanisms of chain initiation, propagation, and termination of the recently discovered N-heterocyclic carbene (NHC)-mediated organocatalytic conjugate-addition polymerization of acrylic monomers. The current study specifically focuses on three commonly used NHCs of vastly different nucleophilicity, 1,3-di-tert-butylimidazolin-2-ylidene (I(t)Bu), 1,3-dimesitylimidazolin-2-ylidene (IMes), and 1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene (TPT), and two representative acrylic monomers, the linear methyl methacrylate (MMA) and its cyclic analog, biomass-derived renewable ?-methyl-?-methylene-?-butyrolactone (MMBL). For MMA, there exhibits an exquisite selectivity of the NHC structure for the three types of reactions it promotes: enamine formation (single-monomer addition) by IMes, dimerization (tail-to-tail) by TPT, and polymerization by I(t)Bu. For MMBL, all three NHCs promote no dimerization but polymerization, with the polymerization activity being highly sensitive to the NHC structure and the solvent polarity. Thus, I(t)Bu is the most active catalyst of the series and converts quantitatively 1000-3000 equiv of MMBL in 1 min or 10,000 equiv in 5 min at room temperature to MMBL-based bioplastics with a narrow range of molecular weights of M(n) = 70-85 kg/mol, regardless of the [MMBL]/[I(t)Bu] ratio employed. The I(t)Bu-catalyzed MMBL polymerization reaches an exceptionally high turnover frequency up to 122 s(-1) and a high initiator efficiency value up to 1600%. Unique chain-termination mechanisms have been revealed, accounting for the production of relative high-molecular-weight linear polymers and the catalytic nature of this NHC-mediated conjugate-addition polymerization. Computational studies have provided mechanistic insights into reactivity and selectivity between two competing pathways for each NHC-monomer zwitterionic adduct, namely enamine formation/dimerization through proton transfer vs polymerization through conjugate addition, and mapped out extensive energy profiles for chain initiation, propagation, and termination steps, thereby satisfactorily explaining the experimental observations. PMID:24245532

  6. Highly efficient deep-blue emitters based on cis and trans N-heterocyclic carbene Pt(II) acetylide complexes: synthesis, photophysical properties, and mechanistic studies.

    PubMed

    Zhang, Yuzhen; Blacque, Olivier; Venkatesan, Koushik

    2013-11-11

    We have synthesized cis and trans N-heterocyclic carbene (NHC) platinum(II) complexes bearing ?-alkynyl ancillary ligands, namely [Pt(dbim)2 (C?CR)2 ] [DBIM=N,N'-didodecylbenzimidazoline-2-ylidene; R=C6 H4 F (4), C6 H5 (5), C6 H2 (OMe)3 (6), C4 H3 S (7), and C6 H4 C?CC6 H5 (8)] and [Pt(ibim)2 (C?CC6 H5 )2 ] (9) (ibim=N,N'-diisopropylbenzimidazoline-2-ylidene), starting from [Pt(cod)(C?CR)2 ] (COD=cyclooctadiene) and 2?equivalents of [dbimH]Br ([ibimH]Br for complexes 9) in the presence of tBuOK and THF. Mechanistic investigations aimed at uncovering the cis to trans isomerization reaction have been performed on the representative cis complex 5?a [Pt(dbim)2 (C?CC6 H5 )2 ] and revealed the isomerization to progress smoothly in good yield when 5?a was treated with catalytic amounts of [Pt(cod)(C?CR)2 ] at 75?°C in THF or when 5?a was heated at 200?°C in the solid state under an inert atmosphere. Detailed examination of the reactions points to the possible involvement, in a catalytic fashion, of a solvent-stabilized Pt(II) dialkyne complex in the former case and a Pt(0) NHC complex in the latter case, for the transformation of the cis isomer to the corresponding trans complex. Thermal stability and the isomerization process in the solid state have been further investigated on the basis of TGA and DSC measurements. X-ray diffraction studies have been carried out to confirm the solid-state structures of 4?b, 5?a, 5?b, and 9?b. All of the synthesized dialkyne complexes 4-9 exhibit phosphorescence in solution, in the solid state at room temperature (RT), and also in frozen solvent glasses at 77?K. The emission wavelengths and quantum yields have been found to be highly tunable as a function of the alkynyl ligand. In particular, the trans isomer of complex 9 in a spin-coated film (10?wt?% in poly(methyl methacrylate), PMMA) exhibits a high phosphorescence quantum yield of 80?%, which is the highest reported for Pt(II) -based deep-blue emitters. Experimental observations and time-dependent density functional theory (TD-DFT) calculations are strongly indicative of the emission being mainly governed by metal-perturbed interligand ((3) IL) charge transfer. PMID:24108420

  7. Constructing !stable Structures: Rank 2 fields

    E-print Network

    Baldwin, John T.

    those first order theories which admit a rudimentary dimension theory as !­stable, superstable or stable that every superstable (and thus every !­stable) pure field (language is field language) is algebraically

  8. Constructing !stable Structures: Rank 2 fields

    E-print Network

    Baldwin, John T.

    those first order theories which admit a rudimentary dimension theory as !­stable, superstable or stable DMS­9510377. 1 #12; Cherlin and Shelah [9] showed that every superstable (and thus every !­stable

  9. Stable glasses from strong liquids

    NASA Astrophysics Data System (ADS)

    Chua, Yeong Zen; Ahrenberg, Mathias; Tylinski, Michael; Ediger, Mark D.; Schick, Christoph

    2015-03-01

    To date, only several materials have been observed to form ultra-stable glasses by vapor deposition. Some authors have suggested that fragility might be a controlling factor in the ability to form stable glasses by vapor deposition, with highly stable glasses only being possible for highly fragile liquids. Glasses of ethylcyclohexane, fragility index 56.5, and 1-pentene, a very small molecule, produced by physical vapor deposition have been characterized by in situ AC chip nanocalorimetry. Since the fragility index of 1-pentene was not available, it was determined as 52 from the calorimetric glass transition temperatures measured in the frequency range from 0.2 Hz to 4 kHz. Ethylcyclohexane and 1-pentene are both strong glass formers, for which possibility of stable glass formation has been questioned. On the contrary, we observed formation of highly stable glasses of ethylcyclohexane and 1-pentene. The results on ethylcyclohexane and 1-pentene will be presented and compared with literature data of other known glass formers.

  10. Metal Stable Isotopes in Paleoceanography

    NASA Astrophysics Data System (ADS)

    Anbar, Ariel D.; Rouxel, Olivier

    2007-05-01

    Considered esoteric only a few years ago, research into the stable isotope geochemistry of transition metals is moving into the geoscience mainstream. Although initial attention focused on the potential use of some of these nontraditional isotope systems as biosignatures, they are now emerging as powerful paleoceanographic proxies. In particular, the Fe and Mo isotope systems are providing information about changes in oxygenation and metal cycling in ancient oceans. Zn, Cu, Tl, and a number of other metals and metalloids also show promise. Here we review the basis of stable isotope fractionation as it applies to these elements, analytical considerations, and the current status and future prospects of this rapidly developing research area.

  11. Decliners > Stables Episodic Memory Task

    E-print Network

    Wisconsin at Madison, University of

    adults enrolled in the Wisconsin Registry for Alzheimer's Prevention (WRAP) who underwent imaging and have been followed with cognitive assessment since 2001. Classification: Based on the longitudinal Rey as either Stable (n=90) or Decliner (n=124). Clinical comparison: 10 MCI patients were recruited from

  12. Texture Descriptors via Stable Distributions

    Microsoft Academic Search

    Pattaraporn Khuwuthyakorn; Antonio Robles-kelly; Jun Zhou

    2008-01-01

    Abstract In this paper, we present a texture descriptor which hinges in the use of the local image statistics so as to recover a compact representation of the texture under study. To this end, here, we make use of stable distributions and their link to Fourier analysis so as to provide a means to compute in a computationally efficient manner

  13. Stable Fluids Jos Stam \\Lambda

    E-print Network

    Toronto, University of

    Stable Fluids Jos Stam \\Lambda Alias wavefront Abstract Building animation tools for fluid of physics­based models for fluid flow can greatly assist in creating such tools. Physical models, unlike key, swirling fluid­like behaviors. Also, the interac­ tion of flows with objects and virtual forces is handled

  14. Synthesis of thermally stable polymers

    NASA Technical Reports Server (NTRS)

    Butler, G. B.

    1978-01-01

    The reaction of bis triazo linediones with divinyl esters and substituted styrenes was investigated. Twenty new polymers were derived via reaction of two previously synthesized bis triazol linediones and four new bis atriazol linediones with eight styrenes. The structure and polymer properties of these thermally stable polymers was examined. The reaction of triazo linediones with enol esters was also considered.

  15. Detection of stable properties in distributed applications

    Microsoft Academic Search

    Jean-Michael Helary; Claude Jard; Noël Plouzeau; Michel Raynal

    1987-01-01

    When evaluated to true, a stable property remains true forever. Such a stable property may character- ize important states of a computation. This is the case of deadlocked or terminated computations. In this paper we expose a general algorithm for the dis- tributed detection of stable properties in distributed applications or systems. This distributed algorithm deals with every stable property

  16. Phase stable RF transport system

    DOEpatents

    Curtin, Michael T. (Los Alamos, NM); Natter, Eckard F. (San Francisco, CA); Denney, Peter M. (Los Alamos, NM)

    1992-01-01

    An RF transport system delivers a phase-stable RF signal to a load, such as an RF cavity of a charged particle accelerator. A circuit generates a calibration signal at an odd multiple frequency of the RF signal where the calibration signal is superimposed with the RF signal on a common cable that connects the RF signal with the load. Signal isolating diplexers are located at both the RF signal source end and load end of the common cable to enable the calibration to be inserted and extracted from the cable signals without any affect on the RF signal. Any phase shift in the calibration signal during traverse of the common cable is then functionally related to the phase shift in the RF signal. The calibration phase shift is used to control a phase shifter for the RF signal to maintain a stable RF signal at the load.

  17. Super-stable Poissonian structures

    NASA Astrophysics Data System (ADS)

    Eliazar, Iddo

    2012-10-01

    In this paper we characterize classes of Poisson processes whose statistical structures are super-stable. We consider a flow generated by a one-dimensional ordinary differential equation, and an ensemble of particles ‘surfing’ the flow. The particles start from random initial positions, and are propagated along the flow by stochastic ‘wave processes’ with general statistics and general cross correlations. Setting the initial positions to be Poisson processes, we characterize the classes of Poisson processes that render the particles’ positions—at all times, and invariantly with respect to the wave processes—statistically identical to their initial positions. These Poisson processes are termed ‘super-stable’ and facilitate the generalization of the notion of stationary distributions far beyond the realm of Markov dynamics.

  18. Stable Stratification for Solar Ponds

    NASA Technical Reports Server (NTRS)

    Mehta, G. D.

    1982-01-01

    Stable density gradient forms in pond saturated with disodium phosphate (DSP). Volume of DSP saturated water tends to develop temperature and density layers. Since tests indicate thermal and density gradients remain in equilibrium at heat removal rates of 60 percent or more of heat input rate, pond containing DSP would be suitable for collecting solar energy and transferring it to heat exchanger for practical use.

  19. Paleoproxies: Heavy Stable Isotope Perspectives

    Microsoft Academic Search

    T. F. Nagler; D. Hippler; C. Siebert; J. D. Kramers

    2002-01-01

    Recent advances in isotope ratio mass spectrometry, namely multiple collector ICP-MS and refined TIMS techniques, will significantly enhance the ability to measure heavy stable isotope fractionation, which will lead to the development of a wide array of process-identifying (bio)-geochemical tools. Thus far research in this area is not easily assessable to scientists outside the isotope field. This is due to

  20. Thermally stable emulsion explosive composition

    SciTech Connect

    Sudweeks, W.B.; Lawrence, L.D.

    1982-03-30

    A thermally stable, cap-sensitive, water-in-oil emulsion explosive composition is described which has a discontinuous aqueous oxidizer salt solution phase containing calcium nitrate, a continuous oil or water-immiscible liquid or organic phase, an emulsifier, and a density reducing agent. The salt solution contains calcium nitrate in an amount of at least 20% by weight based on the total composition. 9 claims.

  1. How Stable Is Stable? Function versus Community Composition

    PubMed Central

    Fernández, Ana; Huang, Suiying; Seston, Sherry; Xing, Jian; Hickey, Robert; Criddle, Craig; Tiedje, James

    1999-01-01

    The microbial community dynamics of a functionally stable, well-mixed, methanogenic reactor fed with glucose were analyzed over a 605-day period. The reactor maintained constant pH and chemical oxygen demand removal during this period. Thirty-six rrn clones from each of seven sampling events were analyzed by amplified ribosomal DNA restriction analysis (ARDRA) for the Bacteria and Archaea domains and by sequence analysis of dominant members of the community. Operational taxonomic units (OTUs), distinguished as unique ARDRA patterns, showed reproducible distribution for three sample replicates. The highest diversity was observed in the Bacteria domain. The 16S ribosomal DNA Bacteria clone library contained 75 OTUs, with the dominant OTU accounting for 13% of the total clones, but just 21 Archaea OTUs were found, and the most prominent OTU represented 50% of the clones from the respective library. Succession in methanogenic populations was observed, and two periods were distinguished: in the first, Methanobacterium formicicum was dominant, and in the second, Methanosarcina mazei and a Methanobacterium bryantii-related organism were dominant. Higher variability in Bacteria populations was detected, and the temporal OTU distribution suggested a chaotic pattern. Although dominant OTUs were constantly replaced from one sampling point to the next, phylogenetic analysis indicated that inferred physiologic changes in the community were not as dramatic as were genetic changes. Seven of eight dominant OTUs during the first period clustered with the spirochete group, although a cyclic pattern of substitution occurred among members within this order. A more flexible community structure characterized the second period, since a sequential replacement of a Eubacterium-related organism by an unrelated deep-branched organism and finally by a Propionibacterium-like species was observed. Metabolic differences among the dominant fermenters detected suggest that changes in carbon and electron flow occurred during the stable performance and indicate that an extremely dynamic community can maintain a stable ecosystem function. PMID:10427068

  2. Constructing !-stable Structures: Rank 2 fields

    E-print Network

    Baldwin, John T.

    as !-stable, superstable or stable; this is a hierarchy with e* *ach class strictly containing the preceding; Cherlin and Shelah [10] showed that every superstable (and thus every !-sta* *ble) pure field (language

  3. Constructing !-stable Structures: Rank 2 fields

    E-print Network

    Baldwin, John T.

    as !-stable, superstable or stable; this is a hierarchy with e* *ach class strictly contain the preceding. 1 #12; Cherlin and Shelah [9] showed that every superstable (and thus every !-stab* *le) pure

  4. Geometric Stable Roommates Esther M. Arkin

    E-print Network

    Introduction The Stable Marriage problem has multidisciplinary interest, as it is well-studied in economics applications [13]. The Stable Roommates problem (SR) is a non-bipartite version of the Stable Marriage problem on Computational Geometry and Graph Theory, Kyoto, June 11-15, 2007. Applied Math and Statistics, Stony Brook

  5. 5, 24252444, 2008 Stable isotopes and

    E-print Network

    Paris-Sud XI, Université de

    BGD 5, 2425­2444, 2008 Stable isotopes and multiple sources M. N. Bugalho et al. Title Page of Biogeosciences Stable isotopes as ecological tracers: an efficient method for assessing the contribution Union. 2425 #12;BGD 5, 2425­2444, 2008 Stable isotopes and multiple sources M. N. Bugalho et al. Title

  6. EXCEPTIONALLY SMALL BALLS IN STABLE TREES

    E-print Network

    Paris-Sud XI, Université de

    EXCEPTIONALLY SMALL BALLS IN STABLE TREES Thomas Duquesne Guanying Wang November 14, 2011 Abstract The -stable trees are random measured compact metric spaces that appear as the scaling limit of Galton-Watson trees whose offspring distribution lies in a -stable domain, (1, 2]. They form a specific class

  7. Uses of stable isotopes in fish ecology

    EPA Science Inventory

    Analyses of fish tissues (other than otoliths) for stable isotope ratios can provide substantial information on fish ecology, including physiological ecology. Stable isotopes of nitrogen and carbon frequently are used to determine the mix of diet sources for consumers. Stable i...

  8. End-on and side-on ?-acid ligand adducts of gold(I): carbonyl, cyanide, isocyanide, and cyclooctyne gold(I) complexes supported by N-heterocyclic carbenes and phosphines.

    PubMed

    Celik, Mehmet Ali; Dash, Chandrakanta; Adiraju, Venkata A K; Das, Animesh; Yousufuddin, Muhammed; Frenking, Gernot; Dias, H V Rasika

    2013-01-18

    N-heterocyclic carbene ligand SIDipp (SIDipp = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) and trimesitylphosphine ligand have been used in the synthesis of gold(I) cyanide, t-butylisocyanide, and cyclooctyne complexes (SIDipp)Au(CN) (3), (Mes(3)P)Au(CN) (4), [(Mes(3)P)(2)Au][Au(CN)(2)] (5), [(SIDipp)Au(CN(t)Bu)][SbF(6)] ([6][SbF(6)]), [(SIDipp)Au(cyclooctyne)][SbF(6)] ([8][SbF(6)]), and [(Mes(3)P)Au(cyclooctyne)][SbF(6)] ([9][SbF(6)]). A detailed computational study has been carried out on these and the related gold(I) carbonyl adducts [(SIDipp)Au(CO)][SbF(6)] ([1][SbF(6)]), [(Mes(3)P)Au(CO)][SbF(6)] ([2][SbF(6)]), and [(Mes(3)P)Au(CN(t)Bu)](+) ([7](+)). X-ray crystal structures of 3, 5, [6][SbF(6)], [8][SbF(6)], and [9][SbF(6)] revealed that they feature linear gold sites. Experimental and computational data show that the changes in ?-acid ligand on (SIDipp)Au(+) from CO, CN(-), CN(t)Bu, cyclooctyne as in [1](+), 3, [6](+), and [8](+) did not lead to large changes in the Au-C(carbene) bond distances. A similar phenomenon was also observed in Au-P distance in complexes [2](+), 4, [7](+), and [9](+) bearing trimesitylphosphine. Computational data show that the Au-L bonds of "naked" [Au-L](+) or SIDipp and Mes(3)P supported [Au-L](+) (L = CO, CN(-), CN(t)Bu to cyclooctyne) have higher electrostatic character than covalent character. The Au?L ?-donation and Au?L ?-back-donation contribute to the orbital term with the former being the dominant component, but the latter is not negligible. In the Au-CO adducts [1](+)and [2](+), the cationic gold center causes the polarization of the C-O ? and ? orbitals toward the carbon end making the coefficients at the two atoms more equal which is mainly responsible for the large blue shift in the CO stretching frequency. The SIDipp and Mes(3)P supported gold(I) complexes of cyanide and isocyanide also exhibit a significant blue shift in ?(CN) compared to that of the free ligands. Calculated results for Au(CO)Cl and Au(CF(3))CO suggest that the experimentally observed blue shift in ?(CO) of these compounds may at least partly be caused by intermolecular forces. PMID:23273108

  9. Stable massive particles at colliders

    SciTech Connect

    Fairbairn, M.; /Stockholm U.; Kraan, A.C.; /Pennsylvania U.; Milstead, D.A.; /Stockholm U.; Sjostrand, T.; /Lund U.; Skands, P.; /Fermilab; Sloan, T.; /Lancaster U.; ,

    2006-11-01

    We review the theoretical motivations and experimental status of searches for stable massive particles (SMPs) which could be sufficiently long-lived as to be directly detected at collider experiments. The discovery of such particles would address a number of important questions in modern physics including the origin and composition of dark matter in the universe and the unification of the fundamental forces. This review describes the techniques used in SMP-searches at collider experiments and the limits so far obtained on the production of SMPs which possess various colour, electric and magnetic charge quantum numbers. We also describe theoretical scenarios which predict SMPs, the phenomenology needed to model their production at colliders and interactions with matter. In addition, the interplay between collider searches and open questions in cosmology such as dark matter composition are addressed.

  10. Dimensionally stable metallic hydride composition

    DOEpatents

    Heung, Leung K. (Aiken, SC)

    1994-01-01

    A stable, metallic hydride composition and a process for making such a composition. The composition comprises a uniformly blended mixture of a metal hydride, kieselguhr, and a ballast metal, all in the form of particles. The composition is made by subjecting a metal hydride to one or more hydrogen absorption/desorption cycles to disintegrate the hydride particles to less than approximately 100 microns in size. The particles are partly oxidized, then blended with the ballast metal and the kieselguhr to form a uniform mixture. The mixture is compressed into pellets and calcined. Preferably, the mixture includes approximately 10 vol. % or more kieselguhr and approximately 50 vol. % or more ballast. Metal hydrides that can be used in the composition include Zr, Ti, V, Nb, Pd, as well as binary, tertiary, and more complex alloys of La, Al, Cu, Ti, Co, Ni, Fe, Zr, Mg, Ca, Mn, and mixtures and other combinations thereof. Ballast metals include Al, Cu and Ni.

  11. Stable density stratification solar pond

    NASA Technical Reports Server (NTRS)

    Lansing, F. L. (inventor)

    1985-01-01

    A stable density-stratification solar pond for use in the collection and storage of solar thermal energy including a container having a first section characterized by an internal wall of a substantially cylindrical configuration and a second section having an internal wall of a substantially truncated conical configuration surmounting the first section in coaxial alignment therewith, the second section of said container being characterized by a base of a diameter substantially equal to the diameter of the first section and a truncated apex defining a solar energy acceptance opening is discussed. A body of immiscible liquids is disposed within the container and comprises a lower portion substantially filling the first section of the container and an upper portion substantially filling the second section of the container, said lower portion being an aqueous based liquid of a darker color than the upper portion and of a greater density. A protective cover plate is removably provided for covering the acceptance opening.

  12. Is slow walking more stable?

    PubMed

    Bruijn, Sjoerd M; van Dieën, Jaap H; Meijer, Onno G; Beek, Peter J

    2009-07-22

    Several efforts have been made to study gait stability using measures derived from nonlinear time-series analysis. The maximum finite time Lyapunov exponent (lambda(max)) quantifies how a system responds to an infinitesimally small perturbation. Recent studies suggested that slow walking leads to lower lambda(max) values, and thus is more stable than fast walking, but these studies suffer from methodological limitations. We studied the effects of walking speed on the amount of kinematic variability and stability in human walking. Trunk motions of 15 healthy volunteers were recorded in 3D during 2 min of treadmill walking at different speeds. From those time series, maximum Lyapunov exponents, indicating short-term and long-term divergence (lambda(S-stride) and lambda(L-stride)), and mean standard deviation (MeanSD) were calculated. lambda(S-stride) showed a linear decrease with increasing speed for forward-backward (AP) movements and quadratic effects (inverted U-shaped) for medio-lateral (ML) and up-down (VT) movements. lambda(L-stride) showed a quadratic effect (inverted U-shaped) of walking speed for AP movements, a linear decrease for ML movements, and a linear increase for VT movements. Moreover, positive correlations between lambda(S) and MeanSD were found for all directions, while lambda(L-stride) and MeanSD were correlated negatively in the AP direction. The different effects of walking speed on lambda(S-stride) and lambda(L-stride) for the different planes suggest that slow walking is not necessarily more stable than fast walking. The absence of a consistent pattern of correlations between lambda(L-stride) and MeanSD over the three directions suggests that variability and stability reflect, at least to a degree, different properties of the dynamics of walking. PMID:19446294

  13. Efficient C–B Bond Formation Promoted by N-Heterocyclic Carbenes. Synthesis of Tertiary and Quaternary B-Substituted Carbons through Metal-Free Catalytic Boron Conjugate Additions to Cyclic and Acyclic ?,?–Unsaturated Carbonyls

    PubMed Central

    Lee, Kang-sang; Zhugralin, Adil R.; Hoveyda, Amir H.

    2009-01-01

    Metal-free, nucleophilic activation of a B–B bond has been exploited in the development of a highly efficient method for conjugate additions of commercially available bis(pinacolato)diboron to cyclic or acyclic ?,?-unsaturated carbonyls. Reactions are readily catalyzed by 2.5–10 mol % of a simple N-heterocyclic carbene (NHC). A variety of cyclic and acyclic unsaturated ketones and esters can serve as substrates. Transformations deliver ?-boryl carbonyls bearing tertiary as well as quaternary B-substituted carbons in up to >98% yield. Preliminary studies indicate that, although related Cu–NHC-catalyzed reactions are equally efficient, the metal-free variant is more functional group tolerant; in contrast to the Cu-catalyzed reactions, the metal-free processes proceed readily in the presence of a terminal alkyne and do not promote concomitant diboration of an aldehyde. Representative functionalization of the resulting boron enolates demonstrates the strong influence of the Lewis acidic B of the ?-boronate. PMID:19432440

  14. The 1:1 co-crystallization of enantiomers of an arene-tethered and ortho-metallated N-heterocyclic carbene ruthenium(II) half-sandwich complex: Synthesis, structural characterization and theoretical study

    NASA Astrophysics Data System (ADS)

    Karab?y?k, Hasan; K?l?nçarslan, Rafet; Aygün, Muhittin; Çetinkaya, Bekir; García-Granda, Santiago

    2008-01-01

    The reaction of [RuCl 2( p-cymene)] 2 with in situ deprotonated NHC precursor 1,3-bis(biphenyl-2-yl)imidazolinium chloride was carried out in p-xylene at 140 °C to produce ?2, in which the NHC moiety acts as a tridentate C,C',C''-ligand. The complex 2 was characterized by NMR spectroscopy and X-ray crystallographic study. Crystallographic analysis combined with computational study regarding the compound, 1-[? 6-(2'-biphenyl)]-3-[2-phenyl-1,2-phenylene]imidazolidin-2-ylidenechlororuthenium(II), 2, reveals that its metal-centered enantiomers are co-crystallized in 1:1 ratio and NHC frame possessing a tridentate coordination mode consists of ?-donation of the carbene carbon, ? 6-arene tethering of terminal biaryl and ? 1-coordination of the biphenyl ring at 2-position. Enantiomers of the complex are packed as asymmetric dimers in solid state formed by C-H⋯Cl type weak H-bonds and C-H⋯? type interactions giving rise to asymmetric chains. Both interactions serve to stabilization of the extended structure.

  15. Mining Stable Roles in RBAC

    NASA Astrophysics Data System (ADS)

    Colantonio, Alessandro; di Pietro, Roberto; Ocello, Alberto; Verde, Nino Vincenzo

    In this paper we address the problem of generating a candidate role-set for an RBAC configuration that enjoys the following two key features: it minimizes the administration cost; and, it is a stable candidate role-set. To achieve these goals, we implement a three steps methodology: first, we associate a weight to roles; second, we identify and remove the user-permission assignments that cannot belong to a role that have a weight exceeding a given threshold; third, we restrict the problem of finding a candidate role-set for the given system configuration using only the user-permission assignments that have not been removed in the second step—that is, user-permission assignments that belong to roles with a weight exceeding the given threshold. We formally show—proof of our results are rooted in graph theory—that this methodology achieves the intended goals. Finally, we discuss practical applications of our approach to the role mining problem.

  16. Stable Isotopes and M&Ms

    NSDL National Science Digital Library

    Roman de Jesus

    Students are often confused by the concepts of stable isotope signatures and conventional notation. This activity is designed to introduce students to the del notation (isotopic signature), fractionation, and end member mixing of stable isotopes using familiar objects disguised as isotopes. The activity does not explain the physical manifestation of why isotopic fractionation occurs, but does explain the concepts that one easily observes when interpreting stable isotope data sets.

  17. Advanced thermally stable jet fuels

    SciTech Connect

    Schobert, H.H.

    1999-01-31

    The Pennsylvania State University program in advanced thermally stable coal-based jet fuels has five broad objectives: (1) Development of mechanisms of degradation and solids formation; (2) Quantitative measurement of growth of sub-micrometer and micrometer-sized particles suspended in fuels during thermal stressing; (3) Characterization of carbonaceous deposits by various instrumental and microscopic methods; (4) Elucidation of the role of additives in retarding the formation of carbonaceous solids; (5) Assessment of the potential of production of high yields of cycloalkanes by direct liquefaction of coal. Future high-Mach aircraft will place severe thermal demands on jet fuels, requiring the development of novel, hybrid fuel mixtures capable of withstanding temperatures in the range of 400--500 C. In the new aircraft, jet fuel will serve as both an energy source and a heat sink for cooling the airframe, engine, and system components. The ultimate development of such advanced fuels requires a thorough understanding of the thermal decomposition behavior of jet fuels under supercritical conditions. Considering that jet fuels consist of hundreds of compounds, this task must begin with a study of the thermal degradation behavior of select model compounds under supercritical conditions. The research performed by The Pennsylvania State University was focused on five major tasks that reflect the objectives stated above: Task 1: Investigation of the Quantitative Degradation of Fuels; Task 2: Investigation of Incipient Deposition; Task 3: Characterization of Solid Gums, Sediments, and Carbonaceous Deposits; Task 4: Coal-Based Fuel Stabilization Studies; and Task 5: Exploratory Studies on the Direct Conversion of Coal to High Quality Jet Fuels. The major findings of each of these tasks are presented in this executive summary. A description of the sub-tasks performed under each of these tasks and the findings of those studies are provided in the remainder of this volume (Sections 1 through 5).

  18. Wavelet Based Estimation for Univariate Stable Laws

    E-print Network

    Gonçalves, Paulo

    Wavelet Based Estimation for Univariate Stable Laws Anestis Antoniadis Laboratoire IMAG to implement. This article describes a fast, wavelet-based, regression-type method for estimating the parameters of a stable distribution. Fourier domain representations, combined with a wavelet multiresolution

  19. Portfolio Analysis in a Stable Paretian Market

    Microsoft Academic Search

    Eugene F. Fama

    1965-01-01

    Recently evidence has come forth which suggests that empirical probability distributions of returns on securities conform better to stable Paretian distributions with infinite variances than to the normal distribution. Using a generalized form of a technique proposed by Sharpe [17] in a recent issue of this journal, this article develops a portfolio analysis model for a stable Paretian market. The

  20. A review of stable water isotopeA review of stable water isotope modellingmodelling

    E-print Network

    Sturm, Christophe "Kristof"

    · Stable water isotope (SWI: H2 18O, HDO) cycle · Equilibrium fractionation · Kinetic fractionation 2 water isotopes in the climate system · Stable water isotope (SWI: H2 18O, HDO) cycle · Equilibrium fractionation · Kinetic fractionation 2. Modelling the stable water isotope cycle · Rayleigh distillation model

  1. Thermally Stable Piezoelectric and Pyroelectric Polymers

    NASA Technical Reports Server (NTRS)

    Simpson, Joycelyn O.; St. Clair, Terry L.

    2006-01-01

    A class of thermally stable piezoelectric and pyroelectric polymers, and an improved method of making them, have been invented. These polymers can be used as substrates for a wide variety of electromechanical transducers, sensors, and actuators.

  2. FREL: A Stable Feature Selection Algorithm.

    PubMed

    Li, Yun; Si, Jennie; Zhou, Guojing; Huang, Shasha; Chen, Songcan

    2015-07-01

    Two factors characterize a good feature selection algorithm: its accuracy and stability. This paper aims at introducing a new approach to stable feature selection algorithms. The innovation of this paper centers on a class of stable feature selection algorithms called feature weighting as regularized energy-based learning (FREL). Stability properties of FREL using L1 or L2 regularization are investigated. In addition, as a commonly adopted implementation strategy for enhanced stability, an ensemble FREL is proposed. A stability bound for the ensemble FREL is also presented. Our experiments using open source real microarray data, which are challenging high dimensionality small sample size problems demonstrate that our proposed ensemble FREL is not only stable but also achieves better or comparable accuracy than some other popular stable feature weighting methods. PMID:25134091

  3. Intrinsically stable light source at telecom wavelengths

    E-print Network

    Monteiro, Fernando; Sanguinetti, Bruno; Zbinden, Hugo

    2013-01-01

    We present a highly stable light source at telecom wavelengths, based on a short erbium doped fiber. The high stability arises from the high inversion of the Er3+ion population. This source is developed to work as a stable reference in radiometric applications and is useful in any application where high stability and/or a large bandwidth are necessary. The achieved long-term stability is 10 ppm.

  4. An improved stable adaptive fuzzy control method

    Microsoft Academic Search

    Kurt Fischle; D. Schroder

    1999-01-01

    Stable adaptive fuzzy control is a self-tuning concept for fuzzy controllers that uses a Lyapunov-based learning algorithm, thus guaranteeing stability of the system plant-controller-learning algorithm and convergence of the plant output to a given reference signal. In the paper, two new methods for stable adaptive fuzzy control are presented. The first method is an extension of an existing concept: it

  5. Stable isotopes and biomarkers in microbial ecology

    Microsoft Academic Search

    H. T. S. Boschker; J. J. Middelburg

    2002-01-01

    The use of biomarkers in combination with stable isotope analysis is a new approach in microbial ecology and a number of papers on a variety of subjects have appeared. We will first discuss the techniques for analysing stable isotopes in biomarkers, primarily gas chromatography-combustion-isotope ratio mass spectrometry, and then describe a number of applications in microbial ecology based on degreesC.

  6. The stable fly: prediction of larval temperature 

    E-print Network

    Foerster, Kenneth Wayne

    1978-01-01

    THE STABLE FLY: PREDICTION OF LARVAL TEMPERATURE A Thesis by KENNETH WAYNE FOERSTER Submitted to the Graduate College of 'v Texas A(M University in partial fulfillment of the requirement for the degree of MASTER OF SCIENCE August 1978 Major...: Prediction of Larval Temperature. (August 1978) Kenneth Wayne Foerster, B. S. , Texas A(M University Chairman of Advisory Committee: Dr. Ivan L. Berry Stable flies do not diapause during the winter, therefore they must avoid freezing temperatures...

  7. Stable vector bundles and string theory

    SciTech Connect

    Gomez, Tomas L.; Sols, Ignacio [ICMAT (CSIC-UAM-UC3M-UCM), Serrano 113bis, 28006 Madrid (Spain); Facultad de Ciencias Matematicas, Universidad Complutense de Madrid, 28040 Madrid (Spain); Lukic, Sergio [Mathematics Department, Imperial College, London SW7 (United Kingdom)

    2009-05-06

    In [4], Braun, He, Ovrut and Pantev proposed a model of string theory (based on the Calabi-Yau 3-fold X) whose low energy limit predicts certain properties of the Standard Model of particle Physics. This model depends on two vector bundles that have to be stable. We calculate the ample cone of X, and prove that one of them is stable, and the other one is not.

  8. Low work function, stable thin films

    DOEpatents

    Dinh, Long N. (Concord, CA); McLean, II, William (Oakland, CA); Balooch, Mehdi (Berkeley, CA); Fehring, Jr., Edward J. (Dublin, CA); Schildbach, Marcus A. (Livermore, CA)

    2000-01-01

    Generation of low work function, stable compound thin films by laser ablation. Compound thin films with low work function can be synthesized by simultaneously laser ablating silicon, for example, and thermal evaporating an alkali metal into an oxygen environment. For example, the compound thin film may be composed of Si/Cs/O. The work functions of the thin films can be varied by changing the silicon/alkali metal/oxygen ratio. Low work functions of the compound thin films deposited on silicon substrates were confirmed by ultraviolet photoelectron spectroscopy (UPS). The compound thin films are stable up to 500.degree. C. as measured by x-ray photoelectron spectroscopy (XPS). Tests have established that for certain chemical compositions and annealing temperatures of the compound thin films, negative electron affinity (NEA) was detected. The low work function, stable compound thin films can be utilized in solar cells, field emission flat panel displays, electron guns, and cold cathode electron guns.

  9. Concentration of stable elements in food products

    SciTech Connect

    Montford, M.A.; Shank, K.E.; Hendricks, C.; Oakes, T.W.

    1980-01-01

    Food samples were taken from commercial markets and analyzed for stable element content. The concentrations of most stable elements (Ag, Al, As, Au, Ba, Br, Ca, Ce, Cl, Co, Cr, Cs, Cu, Fe, Hf, I, K, La, Mg, Mn, Mo, Na, Rb, Sb, Sc, Se, Sr, Ta, Th, Ti, V, Zn, Zr) were determined using multiple-element neutron activation analysis, while the concentrations of other elements (Cd, Hg, Ni, Pb) were determined using atomic absorption. The relevance of the concentrations found are noted in relation to other literature values. An earlier study was extended to include the determination of the concentration of stable elements in home-grown products in the vicinity of the Oak Ridge National Laboratory. Comparisons between the commercial and local food-stuff values are discussed.

  10. Stable Isotope Enrichment Capabilities at ORNL

    SciTech Connect

    Egle, Brian [ORNL; Aaron, W Scott [ORNL; Hart, Kevin J [ORNL

    2013-01-01

    The Oak Ridge National Laboratory (ORNL) and the US Department of Energy Nuclear Physics Program have built a high-resolution Electromagnetic Isotope Separator (EMIS) as a prototype for reestablishing a US based enrichment capability for stable isotopes. ORNL has over 60 years of experience providing enriched stable isotopes and related technical services to the international accelerator target community, as well as medical, research, industrial, national security, and other communities. ORNL is investigating the combined use of electromagnetic and gas centrifuge isotope separation technologies to provide research quantities (milligram to several kilograms) of enriched stable isotopes. In preparation for implementing a larger scale production facility, a 10 mA high-resolution EMIS prototype has been built and tested. Initial testing of the device has simultaneously collected greater than 98% enriched samples of all the molybdenum isotopes from natural abundance feedstock.

  11. Clinically stable angina pectoris is not necessarily associated with histologically stable atherosclerotic plaques

    Microsoft Academic Search

    A. C. van der Wal; A. E. Becker; K. T. Koch; J. J. Piek; P. Teeling; C. M. van der Loos; G. K. David

    1996-01-01

    OBJECTIVE: To investigate the extent of plaque inflammation in culprit lesions of patients with chronic stable angina. DESIGN: Retrospective study. SETTING: Amsterdam reference centre. SUBJECTS: 89 consecutive patients who underwent directional coronary atherectomy, 58 of whom met the following inclusion criteria: chronic stable angina (Canadian Cardiovascular Society classification 1-3 (group 1, n = 28)); unstable angina (Braunwald class II (group

  12. Stable Spatiotemporal Solitons in Bessel Optical Lattices

    NASA Astrophysics Data System (ADS)

    Mihalache, D.; Mazilu, D.; Lederer, F.; Malomed, B. A.; Kartashov, Y. V.; Crasovan, L.-C.; Torner, L.

    2005-07-01

    We investigate the existence and stability of three-dimensional solitons supported by cylindrical Bessel lattices in self-focusing media. If the lattice strength exceeds a threshold value, we show numerically, and using the variational approximation, that the solitons are stable within one or two intervals of values of their norm. In the latter case, the Hamiltonian versus norm diagram has a swallowtail shape with three cuspidal points. The model applies to Bose-Einstein condensates and to optical media with saturable nonlinearity, suggesting new ways of making stable three-dimensional solitons and “light bullets” of an arbitrary size.

  13. Stable isotopes in Lithuanian bioarcheological material

    NASA Astrophysics Data System (ADS)

    Skipityte, Raminta; Jankauskas, Rimantas; Remeikis, Vidmantas

    2015-04-01

    Investigation of bioarcheological material of ancient human populations allows us to understand the subsistence behavior associated with various adaptations to the environment. Feeding habits are essential to the survival and growth of ancient populations. Stable isotope analysis is accepted tool in paleodiet (Schutkowski et al, 1999) and paleoenvironmental (Zernitskaya et al, 2014) studies. However, stable isotopes can be useful not only in investigating human feeding habits but also in describing social and cultural structure of the past populations (Le Huray and Schutkowski, 2005). Only few stable isotope investigations have been performed before in Lithuanian region suggesting a quite uniform diet between males and females and protein intake from freshwater fish and animal protein. Previously, stable isotope analysis has only been used to study a Stone Age population however, more recently studies have been conducted on Iron Age and Late medieval samples (Jacobs et al, 2009). Anyway, there was a need for more precise examination. Stable isotope analysis were performed on human bone collagen and apatite samples in this study. Data represented various ages (from 5-7th cent. to 18th cent.). Stable carbon and nitrogen isotope analysis on medieval populations indicated that individuals in studied sites in Lithuania were almost exclusively consuming C3 plants, C3 fed terrestrial animals, and some freshwater resources. Current investigation demonstrated social differences between elites and country people and is promising in paleodietary and daily life reconstruction. Acknowledgement I thank prof. dr. G. Grupe, Director of the Anthropological and Palaeoanatomical State Collection in Munich for providing the opportunity to work in her laboratory. The part of this work was funded by DAAD. Antanaitis-Jacobs, Indre, et al. "Diet in early Lithuanian prehistory and the new stable isotope evidence." Archaeologia Baltica 12 (2009): 12-30. Le Huray, Jonathan D., and Holger Schutkowski. "Diet and social status during the La Tène period in Bohemia: carbon and nitrogen stable isotope analysis of bone collagen from Kutná Hora-Karlov and Radovesice." Journal of Anthropological Archaeology 24.2 (2005): 135-147. Schutkowski, Holger, et al. "Diet, status and decomposition at Weingarten: trace element and isotope analyses on early mediaeval skeletal material." Journal of Archaeological Science 26.6 (1999): 675-685. Zernitskaya, Valentina, et al. "Vegetation pattern and sedimentation changes in the context of the Lateglacial climatic events: Case study of Staroje Lake (Eastern Belarus)." Quaternary International (2014).

  14. Suppression of Stable Flies on Cattle 

    E-print Network

    Tomberlin, Jeffery K.

    2004-07-01

    Suppression of Stable Flies on Cattle Jeffery K. Tomberlin Assistant Professor and Extension Specialist The Texas A&M University System B ecause of its painful bite, the stable fly is a consider- able pest of livestock and people. Populations... of more than 20 flies per cow can significantly lower income for live- stock producers. Infestations of 50 flies per cow on beef cattle have reduced weight gain by 25 percent and, in dairy cattle, have decreased milk production by 40 to 60 percent...

  15. [(18)F]-NHC-BF3 adducts as water stable radio-prosthetic groups for PET imaging.

    PubMed

    Chansaenpak, Kantapat; Wang, Mengzhe; Wu, Zhanhong; Zaman, Rehmat; Li, Zibo; Gabbaï, François P

    2015-07-21

    The radiofluorination of N-heterocyclic carbene (NHC) boron trifluoride adducts affords novel [(18)F]-positron emission tomography probes which resist hydrolytic fluoride release. The labelling protocol relies on an (18)F-(19)F isotopic exchange reaction promoted by the Lewis acid SnCl4. Modification of the NHC backbone with a maleimide functionality provides access to a model peptide conjugate which shows no evidence of defluorination when imaged in vivo. PMID:26144217

  16. Dynamically stable magnetic suspension/bearing system

    DOEpatents

    Post, Richard F. (Walnut Creek, CA)

    1996-01-01

    A magnetic bearing system contains magnetic subsystems which act together to support a rotating element in a state of dynamic equilibrium. However, owing to the limitations imposed by Earnshaw's Theorem, the magnetic bearing systems to be described do not possess a stable equilibrium at zero rotational speed. Therefore, mechanical stabilizers are provided, in each case, to hold the suspended system in equilibrium until its speed has exceeded a low critical speed where dynamic effects take over, permitting the achievement of a stable equilibrium for the rotating object. A state of stable equilibrium is achieved above a critical speed by use of a collection of passive elements using permanent magnets to provide their magnetomotive excitation. The magnetic forces exerted by these elements, when taken together, levitate the rotating object in equilibrium against external forces, such as the force of gravity or forces arising from accelerations. At the same time, this equilibrium is made stable against displacements of the rotating object from its equilibrium position by using combinations of elements that possess force derivatives of such magnitudes and signs that they can satisfy the conditions required for a rotating body to be stably supported by a magnetic bearing system over a finite range of those displacements.

  17. A Temperature-Stable Metal Detector

    Microsoft Academic Search

    S. Chekcheyev

    2009-01-01

    The design of a temperature-stable metal detector is analyzed. A mathematical analysis method was used to find critical points that have influence on the thermal stability of the metal detector. Practical measures for ensuring thermal stability are considered. Thermal test results are described. The improvement of the thermal stability of the metal detector allows one to minimize the risk of

  18. Rapid, stable fluid dynamics for computer graphics

    Microsoft Academic Search

    Michael Kass; Gavin S. P. Miller

    1990-01-01

    We present a new method for animating water based on a simple, rapid and stable solution of a set of partial differential equations resulting from an approximation to the shallow water equations. The approximation gives rise to a version of the wave equation on a height-field where the wave velocity is proportional to the square root of the depth of

  19. A stable adaptive predictive control system

    Microsoft Academic Search

    J. M. MARTIN-SANCHEZ; SIRISH L. SHAH; D. GRANT FISHER

    1984-01-01

    An adaptive, predictive control system (APCS) is described and a formal proof of global stability is presented for the case of multi variable, stable – in verse, time – invariant processes in the presence of bounded, unmeasured disturbances plus process and measurement noise. Global stability is proven in the sense that the process input \\/ output vector remains bounded and

  20. Magneto-hydrodynamically stable axisymmetric mirrors

    Microsoft Academic Search

    Dmitri Ryutov

    2010-01-01

    The achievement of high beta (60%) plasma with near classical confinement in a linear axisymmetric magnetic configuration has sparked interest in the Gas Dynamic Trap concept. The significance of these results is that they can be projected directly to a neutron source for materials testing. The possibility of axisymmetric mirrors (AM) being magneto-hydrodynamically (MHD) stable is also of interest from

  1. Stable transformation of papaya via microprojectile bombardment

    Microsoft Academic Search

    Maureen M. M. Fitch; Richard M. Manshardt; Dennis Gonsalves; Jerry L. Slightom; John C. Sanford

    1990-01-01

    Stable transformation of papaya (Carica papaya L.) has been achieved following DNA delivery via high velocity microprojectiles. Three types of embryogenic tissues, including immature zygotic embryos, freshly explanted hypocotyl sections, and somatic embryos derived from both, were bombarded with tungsten particles carrying chimeric NPTII and GUS genes. All tissue types were cultured prior to and following bombardment on half-strength MS

  2. Most stable structure for hard spheres.

    PubMed

    Koch, Hans; Radin, Charles; Sadun, Lorenzo

    2005-07-01

    The hard sphere model is known to show a liquid-solid phase transition, with the solid expected to be either face centered cubic or hexagonal close packed. The differences in free energy of the two structures are very small and various attempts have been made to determine which structure is the more stable. We contrast the different approaches and extend one. PMID:16090135

  3. Designing stable mechanisms for economic environments

    Microsoft Academic Search

    Paul J. Healy; Laurent Mathevet

    2011-01-01

    We study the design of mechanisms that implement Lindahl or Walrasian allocations and whose Nash equilibria are dynamically stable for a wide class of adaptive dynamics. We argue that supermodularity is not a desirable stability criterion in this mechanism design context, focusing instead on contractive mechanisms. We provide necessary and sufficient conditions for a mechanism to Nash implement Lindahl or

  4. Axisymmetric MHD stable sloshing ion distributions

    SciTech Connect

    Berk, H.L.; Dominguez, N.; Roslyakov, G.V.

    1986-07-01

    The MHD stability of a sloshing ion distribution is investigated in a symmetric mirror cell. Fokker-Planck calculations show that stable configurations are possible for ion injection energies that are at least 150 times greater than the electron temperture. Special axial magnetic field profiles are suggested to optimize the favorable MHD properties.

  5. Strategies for stable composite structural design

    Microsoft Academic Search

    Richard A. Brand

    1992-01-01

    Advanced composites have been effectively used in space applications such as telescopes, optical benches, and metering structures. As the sophistication of optics and instrumentation increases, the need for near-zero outgassing and extremely dimensionally stable composites becomes of paramount importance. Continuing improvements in resin and reinforcing fiber technology have resulted in a wider selection of materials for the composite designer of

  6. VERIFICATION OF A DIMENSIONALLY STABLE SPACE STRUCTURE

    Microsoft Academic Search

    M. KORNMANN; M. GENET; P. JACQUOT; E. SPALINGER; B. BAILLY; A. PRADIER

    2001-01-01

    In a parallel paper of IAF97 congress, the development of a dimensionally very stable carbon\\/carbon telescope is presented. The present paper focuses on the verification of this structure. In order to check the stability of the telescope, the following performances were assessed: — mechanical resonance frequencies and damping,— dimensional stability after a series of thermal cycles,— gravity load deformation,— elastic

  7. Numerically Stable Hidden Markov Model Implementation

    E-print Network

    Borenstein, Elhanan

    Numerically Stable Hidden Markov Model Implementation Tobias P. Mann February 21, 2006 Abstract Application of Hidden Markov Models to long observation sequences entails the computation of extremely small Introduction A practical issue in the use of Hidden Markov Models (HMMs) to model long sequences

  8. Dynamically stable magnetic suspension/bearing system

    DOEpatents

    Post, R.F.

    1996-02-27

    A magnetic bearing system contains magnetic subsystems which act together to support a rotating element in a state of dynamic equilibrium. However, owing to the limitations imposed by Earnshaw`s Theorem, the magnetic bearing systems to be described do not possess a stable equilibrium at zero rotational speed. Therefore, mechanical stabilizers are provided, in each case, to hold the suspended system in equilibrium until its speed has exceeded a low critical speed where dynamic effects take over, permitting the achievement of a stable equilibrium for the rotating object. A state of stable equilibrium is achieved above a critical speed by use of a collection of passive elements using permanent magnets to provide their magnetomotive excitation. The magnetic forces exerted by these elements, when taken together, levitate the rotating object in equilibrium against external forces, such as the force of gravity or forces arising from accelerations. At the same time, this equilibrium is made stable against displacements of the rotating object from its equilibrium position by using combinations of elements that possess force derivatives of such magnitudes and signs that they can satisfy the conditions required for a rotating body to be stably supported by a magnetic bearing system over a finite range of those displacements. 32 figs.

  9. Nuclear Structure: From Stable to Unstable Nuclei

    NASA Astrophysics Data System (ADS)

    Voronov, V. V.

    2015-11-01

    A finite rank separable approximation for Skyrme interactions is applied to study the collective nuclear modes in stable and unstable nuclei. The coupling between one- and two-phonon terms in the wave functions are taken into account. Some possibilities for experimental investigations of the manifestations of the pseudospin symmetry in the spectra of odd nuclei with Z ? 100 are indicated.

  10. Design of Multi-Stable RNA Molecules

    Microsoft Academic Search

    Christophe Flamm; Ivo L. Hofacker; Sebastian Maurer-Stroh; Peter F. Stadler; Martin Zehl

    2000-01-01

    We show that the problem of designing RNA sequences that can fold into multiple stable secondary structures can be transformed into a combinatorial optimization problem that can be solved by means of simple heuristics. Hence it is feasible to design RNA switches with prescribed strucutral alternatives. We discuss the theoretical background and present an efficient tool that allows the design

  11. Stable Fly Project in Campo Grande, Brazil

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Andrew Li, Jerry Hogsette, and Beto Perez de Leon, all USDA, and Lane Foil, LSU, are collaborating as consultants on an Embrapa-funded research project for the control of large stable fly populations associated with sugar cane production in Brazil. Our Brazilian counterpart, Dr. Paulo Cançado, is t...

  12. Stable Fly Project in Campo Grande, Brazil

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Andrew Li, Jerry Hogsette, and Adalberto Pérez de León, all USDA-ARS, and Lane Foil, LSU, are collaborating as consultants on an Embrapa-funded research project for the control of large stable fly populations associated with sugar cane production in Brazil. Our Brazilian counterpart, Dr. Paulo Cança...

  13. Roughness of stable, armored gravel beds

    Microsoft Academic Search

    Basil Gomez

    1993-01-01

    The grain roughness of stable armored beds that formed in a laboratory flume under a range of steady flow conditions on rounded, flat, and angular gravel is analyzed. Gravel roughness geometry is determined from bed surface profiles and vertical photographs. These techniques have been employed in field situations. Thus the methodology is potentially applicable to the analysis of grain roughness

  14. A New Perspective on Stable Models

    Microsoft Academic Search

    Paolo Ferraris; Joohyung Lee; Vladimir Lifschitz

    2007-01-01

    The definition of a stable model has provided a declarative semantics for Prolog programs with negation as failure and has led to the development of answer set programming. In this paper we pro- pose a new definition of that concept, which covers many constructs used in answer set programming (including disjunctive rules, choice rules and con- ditional literals) and, unlike

  15. Sugar feeding in adult stable flies.

    PubMed

    Taylor, David B; Berkebile, Dennis R

    2008-06-01

    Adult stable flies (Stomoxys calcitrans L.) are known to feed readily on sugars in the laboratory. However, little is known concerning the extent of stable fly sugar feeding in wild populations. We examined the frequency of sugar feeding in stable flies collected on Alsynite sticky traps in rural and urban environments. In addition, stable flies were visually examined to determine whether blood was present in the gut. In laboratory studies, sugars were detectable with the anthrone technique in stable flies for approximately 3 d after being imbibed, and blood could be visually detected in the gut for 24-48 h after feeding. Twelve percent of the field-collected flies had detectable sugar with a higher percentage of the urban flies having sugar fed than the rural flies, 21 and 8%, respectively. Female flies sugar fed at a slightly higher rate than males, 13 versus 11%, respectively. Less than 1% of the field-collected flies had blood in their guts. The frequency of observable blood was slightly higher in flies collected in an urban environment compared with those collected in a rural environment and did not differ between male and female flies. The number of flies with both blood and sugar was slightly higher than would be expected based on the frequencies of each alone. Seasonal patterns of both sugar feeding and blood feeding were similar in the rural and urban environments; both peaked in the early summer, May to mid-June, and dropped through the summer and fall. Sugar feeding in the urban environment increased again in October. PMID:18559167

  16. Stable isotope composition of Earth's large lakes

    NASA Astrophysics Data System (ADS)

    Jasechko, S.; Gibson, J. J.; YI, Y.; Birks, S. J.; Sharp, Z. D.

    2011-12-01

    Lakes cover about three percent of Earth's continental area. Large lakes can significantly influence lake shore and regional climates by increasing specific humidity during evaporation and by moderating air temperatures. Stable isotopes of oxygen and hydrogen can be used to quantify lake evaporation, providing a supplementary and often cost-advantageous alternative to conventional hydrologic approaches that require over lake monitoring. Further, stable isotopes in lake sediments are an established tool in paleolimnology; however, interpreting changes to a lake's past isotope composition requires a comprehensive understanding of contemporary controls. Here, ?18O and ?2H values of water in modern lakes exceeding roughly five hundred square kilometres are compiled (n > 35). Voluminous and seasonally mixed lakes - such as the North American Great Lakes - have the most homogenous stable isotope compositions, while perennially-stratified and shallow lakes show greater variability. A rudimentary stable isotope mass balance is used to assess evaporation fluxes from large lakes on Earth. The approach taken simultaneously constrains evaporation outputs for both oxygen and hydrogen stable isotopes by accounting for lake effects on the overlying atmosphere. Model development highlights important considerations such as isotopic stratification (Tanganyika), disequilibrium isotopic mass balances (Baikal), and non-steady hydrologic balances. Further, the isotope composition of Earth's continental surface water reservoir is calculated. This value - weighted to volume - is ?18O = -7.5±1.7 per mille relative to standard mean ocean water. The compiled data may be a useful tracer of continental evaporate in global atmospheric water cycle studies and could be coupled to climate models capable of incorporating oxygen-18 and deuterium tracers to improve or validate calculations of lake effects on regional water cycling.

  17. Arithmetic Brownian motion subordinated by tempered stable and inverse tempered stable processes

    E-print Network

    Agnieszka Wy?oma?ska

    2012-03-05

    In the last decade the subordinated processes have become popular and found many practical applications. Therefore in this paper we examine two processes related to time-changed (subordinated) classical Brownian motion with drift (called arithmetic Brownian motion). The first one, so called normal tempered stable, is related to the tempered stable subordinator, while the second one - to the inverse tempered stable process. We compare the main properties (such as probability density functions, Laplace transforms, ensemble averaged mean squared displacements) of such two subordinated processes and propose the parameters' estimation procedures. Moreover we calibrate the analyzed systems to real data related to indoor air quality.

  18. Biological populations with nonoverlapping generations: stable points, stable cycles, and chaos.

    PubMed

    May, R M

    1974-11-15

    Some of the simplest nonlinear difference equations describing the growth of biological populations with nonoverlapping generations can exhibit a remarkable spectrum of dynamical behavior, from stable equilibrium points, to stable cyclic oscillations between 2 population points, to stable cycles with 4, 8, 16, . . . points, through to a chaotic regime in which (depending on the initial population value) cycles of any period, or even totally aperiodic but boundedpopulation fluctuations, can occur. This rich dynamical structure is overlooked in conventional linearized analyses; its existence in such fully deterministic nonlinear difference equations is a fact of considerable mathematical and ecological interest. PMID:4412202

  19. Overview and first results from Project STABLE (Stable Boundary Layer Experiment)

    NASA Astrophysics Data System (ADS)

    Weber, A. H.; Kurzeja, R. J.

    The STABLE project (STAble Boundary Layer Experiment) is a multiyear research effort conceived in 1984 by the Savannah River Laboratory (SRL) and planned by several research groups to study turbulence and diffusion in the stable boundary layer (SBL). The program was jointly planned by Department of Energy (DOE) affiliated laboratories and universities including SRL, Atmospheric Turbulence and Diffusion Division (ATDD) of the National Oceanic and Atmospheric Administration (NOAA), Argonne National Laboratory (ANL), North Carolina State University (NCSU), and The Pennsylvania State University. STABLE's goals are to determine the spatial and temporal distribution of turbulent events during the nighttime, to determine the validity of present models and theories in describing the structure and evolution of the SBL, to determine the role of waves and intermittent turbulence in dispersing chemicals, and to determine better parameterization for describing the mean state and intermittent events in the SBL. By taking advantage of special facility, the program seeks to economize effort and cost.

  20. Synthesis on evaporation partitioning using stable isotopes

    NASA Astrophysics Data System (ADS)

    Coenders-Gerrits, Miriam; Bogaard, Thom; Wenninger, Jochen; Jonson Sutanto, Samuel

    2015-04-01

    Partitioning of evaporation into productive (transpiration) and non-productive evaporation (interception, soil evaporation) is of highest importance for water management practices, irrigation scheme design, and climate modeling. Despite this urge, the magnitude of the ratio of transpiration over total evaporation is still under debate and poorly understood due to measuring difficulties. However, with the current development in isotope measuring devices, new opportunities arise to untangle the partitioning of evaporation. In this paper we synthesize the opportunities and limitations using stable water isotopes in evaporation partitioning. We will analyze a set of field as well as laboratory studies to demonstrate the different evaporation components for various climate and vegetation conditions using stable isotopes 18O/16O and 2H/1H. Experimental data on evaporation partitioning of crops, grass, shrubs and trees are presented and we will discuss the specific experimental set-ups and data collection methods. The paper will be a synthesis of these studies.

  1. Strategies for stable composite structural design

    NASA Astrophysics Data System (ADS)

    Brand, Richard A.

    1992-12-01

    Advanced composites have been effectively used in space applications such as telescopes, optical benches, and metering structures. As the sophistication of optics and instrumentation increases, the need for near-zero outgassing and extremely dimensionally stable composites becomes of paramount importance. Continuing improvements in resin and reinforcing fiber technology have resulted in a wider selection of materials for the composite designer of dimensionally stable structures. Additional improvements in metal sealing techniques promise unprecedented long-term environmental stability. These new options allow the designer to develop a dimensional stability strategy which conforms to design requirements and yields an optimum, cost-effective composite design approach. This paper addresses the major stability issues in composites and how stability can be predicted for long-term applications, along with design options to achieve program goals. Low-moisture-absorbing composites based on cyanate esters, metal sealing techniques, and long-range stability are also addressed.

  2. Stable Throughput in a Cognitive Wireless Network

    E-print Network

    Fanous, Anthony

    2012-01-01

    We study, from a network layer perspective, the effect of an Ad-Hoc secondary network with N nodes randomly accessing the spectrum licensed to a primary node during the idle slots of the primary user. If the sensing is perfect, then the secondary nodes do not interfere with the primary node and hence do not affect its stable throughput. In case of imperfect sensing, it is shown that if the primary user's arrival rate is less than some calculated finite value, cognitive nodes can employ any transmission power or probabilities without affecting the primary user's stability; otherwise, the secondary nodes should control their transmission parameters to reduce the interference on the primary. It is also shown that in contrast with the primary's maximum stable throughput which strictly decreases with increased sensing errors, the throughput of the secondary nodes might increase with sensing errors as more transmission opportunities become available to them. Finally, we explore the use of the secondary nodes as rel...

  3. Stable Stochastic Dynamics in Yeast Cell Cycle

    PubMed Central

    Okabe, Yurie; Sasai, Masaki

    2007-01-01

    Chemical reactions in cells are subject to intense stochastic fluctuations. An important question is how the fundamental physiological behavior of the cell is kept stable against those noisy perturbations. In this study, a stochastic model of the cell cycle of budding yeast was constructed to analyze the effects of noise on the cell-cycle oscillation. The model predicts intense noise in levels of mRNAs and proteins, and the simulated protein levels explain the observed statistical tendency of noise in populations of synchronous and asynchronous cells. Despite intense noise in levels of proteins and mRNAs, the cell cycle is stable enough to bring the largely perturbed cells back to the physiological cyclic oscillation. The model shows that consecutively appearing fixed points are the origin of this stability of the cell cycle. PMID:17704157

  4. Unstable-stable resonators with toroidal mirrors.

    PubMed

    Borghese, A; Canevari, R; Donati, V; Garifo, L

    1981-10-15

    A resonator with toroidal mirrors is described. This resonator behaves like an off-axis unstable confocal resonator in one transverse dimension and like an on-axis concave-convex stable resonator in the other orthogonal dimension. Some experimental results are reported for a fast flow high power cw-CO(2) laser whose transverse cross section is restricted in the stable-resonator direction. These cavities allow an output laser beam with a fully illuminated cross section which is well suited for focusing. Moreover, the fraction of the available laser power which may be concentrated in the central lobe of the focal plane intensity distribution is 2.5-4.5 times higher than other unstable resonators with similarly restricted modal volumes. Finally the alignment requirements are examined. PMID:20372215

  5. A stable Ti-based quasicrystal

    SciTech Connect

    Kelton, K.F.; Kim, W.J.; Stroud, R.M. [Department of Physics, Washington University, St. Louis, Missouri 63130 (United States)] [Department of Physics, Washington University, St. Louis, Missouri 63130 (United States)

    1997-06-01

    The thermal stability of the icosahedral phase (i phase) in Ti{sub 45}Zr{sub 38}Ni{sub 17} alloys is demonstrated. As-cast alloys containing initially only the C14 hexagonal Laves and {alpha}-solid-solution phases transformed primarily to the icosahedral phase upon annealing in vacuum for 64 h at 570{degree}C. This confirms previous evidence for i-phase stability and firmly establishes this quasicrystal as the first nonaluminum stable icosahedral phase. Diffraction data show that this stable i phase is primitive; energy dispersive x-ray spectroscopy measurements place its composition near Ti{sub 41.5}Zr{sub 41.5}Ni{sub 17}. These and other results suggest that the structure of this i phase is similar to that of i(AlLiCu). {copyright} {ital 1997 American Institute of Physics.}

  6. Stable chaos in fluctuation driven neural circuits

    E-print Network

    David Angulo-Garcia; Alessandro Torcini

    2014-03-03

    We study the dynamical stability of pulse coupled networks of leaky integrate-and-fire neurons against infinitesimal and finite perturbations. In particular, we compare current versus fluctuations driven networks, the former (latter) is realized by considering purely excitatory (inhibitory) sparse neural circuits. In the excitatory case the instabilities of the system can be completely captured by an usual linear stability (Lyapunov) analysis, on the other hand the inhibitory networks can display the coexistence of linear and nonlinear instabilities. The nonlinear effects are associated to finite amplitude instabilities, which have been characterized in terms of suitable indicators. For inhibitory coupling one observes a transition from chaotic to non chaotic dynamics by decreasing the pulse width. For sufficiently fast synapses the system, despite showing an erratic evolution, is linearly stable, thus representing a prototypical example of Stable Chaos.

  7. Stable field emission from nanoporous silicon carbide.

    PubMed

    Kang, Myung-Gyu; Lezec, Henri J; Sharifi, Fred

    2013-02-15

    We report on a new type of stable field emitter capable of electron emission at levels comparable to thermal sources. Such an emitter potentially enables significant advances in several important technologies which currently use thermal electron sources. These include communications through microwave electronics, and more notably imaging for medicine and security where new modalities of detection may arise due to variable-geometry x-ray sources. Stable emission of 6 A cm(-2) is demonstrated in a macroscopic array, and lifetime measurements indicate these new emitters are sufficiently robust to be considered for realistic implementation. The emitter is a monolithic structure, and is made in a room-temperature process. It is fabricated from a silicon carbide wafer, which is formed into a highly porous structure resembling an aerogel, and further patterned into an array. The emission properties may be tuned both through control of the nanoscale morphology and the macroscopic shape of the emitter array. PMID:23324430

  8. Thermally Stable, Piezoelectric and Pyroelectric Polymeric Substrates

    NASA Technical Reports Server (NTRS)

    Simpson, Joycely O. (Inventor); St.Clair, Terry L. (Inventor)

    1999-01-01

    A thermally stable, piezoelectric and pyroelectric polymeric substrate was prepared. This thermally stable, piezoelectric and pyroelectric polymeric substrate may be used to prepare electromechanical transducers, thermomechanical transducers, accelerometers. acoustic sensors, infrared sensors, pressure sensors, vibration sensors, impact sensors, in-situ temperature sensors, in-situ stress/strain sensors, micro actuators, switches, adjustable fresnel lenses, speakers, tactile sensors. weather sensors, micro positioners, ultrasonic devices, power generators, tunable reflectors, microphones, and hydrophones. The process for preparing these polymeric substrates includes: providing a polymeric substrate having a softening temperature greater than 1000 C; depositing a metal electrode material onto the polymer film; attaching a plurality of electrical leads to the metal electrode coated polymeric substrate; heating the metal electrode coated polymeric substrate in a low dielectric medium; applying a voltage to the heated metal electrode coated polymeric substrate to induce polarization; and cooling the polarized metal electrode coated polymeric electrode while maintaining a constant voltage.

  9. Compact and stable multibeam fiber injector

    SciTech Connect

    Collins, L. F., LLNL

    1998-07-01

    A compact and stable 20-beam injector was built for launching laser light into fibers for Fabry Perot velocity measurements of shock-driven surfaces. The fiber injector uses commercial mounts on mini-rails. Dielectric-coated beamsplitters provide accurate amplitude division. Minimal adjustments for stable operation are permitted by the use of a real-time video-viewer. The video system includes a non-linear camera for CW alignment and a linearized camera with a frame grabber for pulsed measurement and analysis. All 20-injection points are displayed on a single monitor. Optical requirements are given for image relay and magnification. Stimulated Brillouin scattering limitations on high-power are quantified.

  10. Use of stable isotopes to determine compliance.

    PubMed

    Schwarcz, H P

    1984-12-01

    The natural variation in the abundance of stable isotopes of light elements (C, H, O, N) in humans is less than 0.5%. Much larger variations can be induced through administration of drugs labeled with enriched isotopes of these elements. Such labels thus can be used as tracers of compliance. Variations of several percent can be generated without adverse physiological effect. An example is presented of the use of deuterium oxide as a tracer, and a scheme of sampling moisture in expired air is proposed, in which the subject can easily collect a sample and present it for rapid analysis. Tracer levels can be used to estimate the degree of compliance. The labeled compound can be selected to match the drug being tested with respect to residence time in the body. Except for deuterium, the cost of such stable isotope tracers is at present prohibitive. The main problem with the use of stable isotopes in compliance studies is the cost of the tracer, a biologically acceptable substance labeled with a rare-stable isotope. Our original experiments were carried out using 13C-glucose, which costs at present about $600/g. To carry out a tracer experiment on an individual, approximately 10 mg of uniformly labeled tracer would be administered, which would result in a 5% shift of the 13C/12C ratio, which is easily detectable. To minimize the cost of such a study, we proposed utilizing the cheapest enriched light isotope that is available, namely, deuterium. Using a ratio-detecting mass spectrometer in which a sample is compared with a standard, it is possible to detect enrichment or depletion of deuterium with respect to 1H at the level of 0.1%.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:6518787

  11. Magneto-hydrodynamically stable axisymmetric mirrors

    Microsoft Academic Search

    D. D. Ryutov; H. L. Berk; B. I. Cohen; A. W. Molvik; T. C. Simonen

    2011-01-01

    Making axisymmetric mirrors magnetohydrodynamically (MHD) stable opens up exciting opportunities for using mirror devices as neutron sources, fusion-fission hybrids, and pure-fusion reactors. This is also of interest from a general physics standpoint (as it seemingly contradicts well-established criteria of curvature-driven instabilities). The axial symmetry allows for much simpler and more reliable designs of mirror-based fusion facilities than the well-known quadrupole

  12. Protein-based stable isotope probing

    Microsoft Academic Search

    Nico Jehmlich; Frank Schmidt; Jana Seifert; Felipe Bastida; Martin von Bergen; Hans-Hermann Richnow; Carsten Vogt; Martin Taubert

    2010-01-01

    We describe a stable isotope probing (SIP) technique that was developed to link microbe-specific metabolic function to phylogenetic information. Carbon (13C)- or nitrogen (15N)-labeled substrates (typically with >98% heavy label) were used in cultivation experiments and the heavy isotope incorporation into proteins (protein-SIP) on growth was determined. The amount of incorporation provides a measure for assimilation of a substrate, and

  13. Uncertainty in source partitioning using stable isotopes

    Microsoft Academic Search

    Donald L. Phillips; Jillian W. Gregg

    2001-01-01

    Stable isotope analyses are often used to quan- tify the contribution of multiple sources to a mixture, such as proportions of food sources in an animal's diet, or C3 and C4 plant inputs to soil organic carbon. Linear mixing models can be used to partition two sources with a single isotopic signature (e.g., ?13C) or three sources with a second

  14. Thermally Stable and Flame Retardant Elastomeric Nanocomposites

    Microsoft Academic Search

    O. Cerin; G. Fontaine; S. Duquesne; S. Bourbigot

    \\u000a This chapter is dedicated to thermally stable and flame retardant elastomeric composites. Two approaches are considered: the\\u000a synthesis of elastomeric nanocomposites, where the nanoparticles are dispersed at the nanoscale, and the incorporation of\\u000a nanofillers at high loadings where agglomerate of nanoparticles are observed in the elastomeric matrix. The chapter is mainly\\u000a focused on the key parameter influencing the flame retardancy,

  15. Stable H2-optimal controller synthesis

    Microsoft Academic Search

    J. R. Corrado; R. Scott Erwin; Dennis S. Bernstein; W. M. Haddad

    1997-01-01

    This paper considers fixed-structure stable H2-optimal controller synthesis using a multiobjective optimization technique. The problem is presented in a decentralized static output feedback framework developed for fixed-structure dynamic controller synthesis. A quasi-Newton\\/continuation algorithm is used to compute solutions to the necessary conditions. To demonstrate the approach, a numerical example is considered, which consists of a second-order spring-mass-damper system pulled from

  16. The Weinstein conjecture for stable Hamiltonian structures

    Microsoft Academic Search

    Michael Hutchings; Clifford Henry Taubes

    2009-01-01

    We use the equivalence between embedded contact homology and Seiberg-Witten\\u000aFloer homology to obtain the following improvements on the Weinstein\\u000aconjecture. Let Y be a closed oriented connected 3-manifold with a stable\\u000aHamiltonian structure, and let R denote the associated Reeb vector field on Y.\\u000aWe prove that if Y is not a T^2-bundle over S^1, then R has a

  17. Constructing simple stable descriptions for image partitioning

    Microsoft Academic Search

    Yvan G. Leclerc

    1989-01-01

    A new formulation of the image partitioning problem is presented: construct a complete and stable description of an image-in terms of a specified descriptive language-that is simplest in the sense of being shortest. We show that a descriptive language limited to a low-order polynomial description of the intensity variation within each region and a chain-code-like description of the region boundaries

  18. Quantifying uncertainty in stable isotope mixing models

    NASA Astrophysics Data System (ADS)

    Davis, Paul; Syme, James; Heikoop, Jeffrey; Fessenden-Rahn, Julianna; Perkins, George; Newman, Brent; Chrystal, Abbey E.; Hagerty, Shannon B.

    2015-05-01

    Mixing models are powerful tools for identifying biogeochemical sources and determining mixing fractions in a sample. However, identification of actual source contributors is often not simple, and source compositions typically vary or even overlap, significantly increasing model uncertainty in calculated mixing fractions. This study compares three probabilistic methods, Stable Isotope Analysis in R (SIAR), a pure Monte Carlo technique (PMC), and Stable Isotope Reference Source (SIRS) mixing model, a new technique that estimates mixing in systems with more than three sources and/or uncertain source compositions. In this paper, we use nitrate stable isotope examples (?15N and ?18O) but all methods tested are applicable to other tracers. In Phase I of a three-phase blind test, we compared methods for a set of six-source nitrate problems. PMC was unable to find solutions for two of the target water samples. The Bayesian method, SIAR, experienced anchoring problems, and SIRS calculated mixing fractions that most closely approximated the known mixing fractions. For that reason, SIRS was the only approach used in the next phase of testing. In Phase II, the problem was broadened where any subset of the six sources could be a possible solution to the mixing problem. Results showed a high rate of Type I errors where solutions included sources that were not contributing to the sample. In Phase III some sources were eliminated based on assumed site knowledge and assumed nitrate concentrations, substantially reduced mixing fraction uncertainties and lowered the Type I error rate. These results demonstrate that valuable insights into stable isotope mixing problems result from probabilistic mixing model approaches like SIRS. The results also emphasize the importance of identifying a minimal set of potential sources and quantifying uncertainties in source isotopic composition as well as demonstrating the value of additional information in reducing the uncertainty in calculated mixing fractions.

  19. Stable complexity and simplicial volume of manifolds

    E-print Network

    Francaviglia, Stefano; Martelli, Bruno

    2012-01-01

    Let the Delta-complexity of a closed manifold M be the minimum number of simplices in a triangulation of M. Such a quantity is clearly submultiplicative with respect to finite coverings, and by taking the appropriate infimum on all finite coverings of M we can promote it to a multiplicative invariant, a characteristic number already considered by Milnor and Thurston, which we call the "stable Delta-complexity" of M. We study here the relation between the stable Delta-complexity of M and Gromov's simplicial volume ||M||. We prove that the two characteristic numbers coincide on any irreducile 3-manifold M whose JSJ decomposition consists of Seifert pieces and/or hyperbolic pieces commensurable with the figure-eight knot complement. We do not know if they coincide on any irreducible 3-manifolds with infinite fundamental group: they do if a particular three-dimensional version of the Ehrenpreis conjecture holds. On the other hand, we show that ||M|| is strictly smaller than C_n times the stable Delta-complexity o...

  20. Detonation of Meta-stable Clusters

    SciTech Connect

    Kuhl, Allen; Kuhl, Allen L.; Fried, Laurence E.; Howard, W. Michael; Seizew, Michael R.; Bell, John B.; Beckner, Vincent; Grcar, Joseph F.

    2008-05-31

    We consider the energy accumulation in meta-stable clusters. This energy can be much larger than the typical chemical bond energy (~;;1 ev/atom). For example, polymeric nitrogen can accumulate 4 ev/atom in the N8 (fcc) structure, while helium can accumulate 9 ev/atom in the excited triplet state He2* . They release their energy by cluster fission: N8 -> 4N2 and He2* -> 2He. We study the locus of states in thermodynamic state space for the detonation of such meta-stable clusters. In particular, the equilibrium isentrope, starting at the Chapman-Jouguet state, and expanding down to 1 atmosphere was calculated with the Cheetah code. Large detonation pressures (3 and 16 Mbar), temperatures (12 and 34 kilo-K) and velocities (20 and 43 km/s) are a consequence of the large heats of detonation (6.6 and 50 kilo-cal/g) for nitrogen and helium clusters respectively. If such meta-stable clusters could be synthesized, they offer the potential for large increases in the energy density of materials.

  1. A peculiar stable region around Pluto

    NASA Astrophysics Data System (ADS)

    Giuliatti Winter, S. M.; Winter, O. C.; Vieira Neto, E.; Sfair, R.

    2014-04-01

    Giuliatti Winter et al. found several stable regions for a sample of test particles located between the orbits of Pluto and Charon. One peculiar stable region in the space of the initial orbital elements is located at a = (0.5d, 0.7d) and e = (0.2, 0.9), where a and e are the initial semimajor axis and eccentricity of the particles, respectively, and d is the Pluto-Charon distance. This peculiar region (hereafter called the sailboat region) is associated with a family of periodic orbits derived from the planar, circular, restricted three-body problem (Pluto-Charon-particle). In this work, we study the origin of this stable region by analysing the evolution of such family of periodic orbits. We show that they are not in resonances with Charon. The period of the periodic orbit varies along the family, decreasing with the increase of the Jacobi constant. We also explore the extent of the sailboat region by adopting different initial values of the orbital inclination (I) and argument of the pericentre (?) of the particles. The sailboat region is present for I = [0°, 90°] and for two intervals of ?, ? = [-10°, 10°] and (160°, 200°). A crude estimative of the size of the hypothetical bodies located at the sailboat region can be derived by computing the tidal damping in their eccentricities. If we neglect the orbital evolution of Pluto and Charon, the time-scale for circularization of their orbits is longer than the age of the Solar system for bodies smaller than 500 m in radius.

  2. Isotropic turbulence, stable layers: facts or fictions?

    NASA Astrophysics Data System (ADS)

    Lovejoy, S.; Tuck, A.; Hovde, S.; Schertzer, D.

    2007-05-01

    Using state of the art drop sonde data (from 237 sondes over the Pacific) we examine two classical and fundamental idealizations of atmospheric science showing that they are untenable in the light of the vertical structure. The first is the notion of stable atmospheric layers. This is used for understanding atmospheric dynamics and thermodynamics, including the most advanced dynamical meteorological notions such as potential vorticity. Using the drop sonde data, we show that each apparently stable layer is actually composed of a hierarchy of unstable layers themselves with embedded stable sublayers, each with unstable sub-sub layers etc. i.e. in a Russian doll-like fractal hierarchy whose dimension we estimate. We therefore argue that the notion is untenable and must be replaced by modern scaling notions. The second idealization we examine is the turbulence assumption of isotropy. If we include intermittency, Kolmorogov's landmark proposal that fully developed turbulence has an "inertial subrange" with isotropic energy spectrum E(k)=k**-beta with beta=5/3 has apparently been spectacularly confirmed in both the horizontal direction and in the time domain (k is a wavenumber). For gradients over a horizontal distance deltax this implies deltav=deltaz**Hh (Hh=1/3 corresponds to beta=5/3). Remarkably, Hv for gradients over vertical distances deltaz (deltav=deltaz**Hv) has not been seriously investigated. Using drop sonde data of horizontal wind, we find that from scales of 5 m to 10 km from the surface layer through to the top of the troposphere, Hv is close to (or larger) than the Bolgiano-Obukhov value 3/5. Hv greater than Hh implies that a) the atmosphere becomes progressively less stratified at smaller scales although in a scaling way; b) that at most a single (roughly) isotropic "sphero- scale" exists (often in the range 1-100 cm).

  3. Stable isotopic analyses in paleoclimatic reconstruction

    SciTech Connect

    Wigand, P.E. [Univ. and Community College System of Nevada, Reno, NV (United States)

    1995-09-01

    Most traditional paleoclimatic proxy data have inherent time lags between climatic input and system response that constrain their use in accurate reconstruction of paleoclimate chronology, scaling of its variability, and the elucidation of the processes that determine its impact on the biotic and abiotic environment. With the exception of dendroclimatology, and studies of short-lived organisms and pollen recovered from annually varved lacustrine sediments, significant periods of time ranging from years, to centuries, to millennia may intervene between climate change and its first manifestation in paleoclimatic proxy data records. Reconstruction of past climate through changes in plant community composition derived from pollen sequences and plant remains from ancient woodrat middens, wet environments and dry caves all suffer from these lags. However, stable isotopic analyses can provide more immediate indication of biotic response to climate change. Evidence of past physiological response of organisms to changes in effective precipitation as climate varies can be provided by analyses of the stable isotopic content of plant macrofossils from various contexts. These analyses consider variation in the stable isotopic (hydrogen, oxygen and carbon) content of plant tissues as it reflects (1) past global or local temperature through changes in meteoric (rainfall) water chemistry in the case of the first two isotopes, and (2) plant stress through changes in plant respiration/transpiration processes under differing water availability, and varying atmospheric CO, composition (which itself may actually be a net result of biotic response to climate change). Studies currently being conducted in the Intermountain West indicate both long- and short-term responses that when calibrated with modem analogue studies have the potential of revealing not only the timing of climate events, but their direction, magnitude and rapidity.

  4. 2. Historic American Buildings Survey 'Stable and Smoke House' Photocopy ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. Historic American Buildings Survey 'Stable and Smoke House' Photocopy of Plate XXX From: Brown, Glenn, The Octagon, Washington, N.D. - Octagon House, Stable, 1799 New York Avenue Northwest, Washington, District of Columbia, DC

  5. Stable carbon isotope measurements using laser spectroscopy

    NASA Technical Reports Server (NTRS)

    Sauke, T. B.; Becker, J. F.

    1991-01-01

    The 2300 cm(exp -1) spectral region is especially interesting because (12)CO2 and (13)CO2 bands overlap in such a way that their rotational lines have approximately equal absorbance at the anticipated isotopic ratio (approximately 90) of carbon on Earth and Mars. Pairs of rotational lines we have studied are separated by as little as 0.050 cm(exp -1), but are well resolved with a tunable diode laser. Using sophisticated sweep integration and signal averaging techniques, we have measured the stable isotope ratio in carbon dioxide to a precision of better than 1 percent.

  6. Stable Configurations of the ? Andromedae Planetary System

    NASA Astrophysics Data System (ADS)

    Deitrick, Russell; Barnes, Rory; McArthur, Barbara; Quinn, Thomas R.; Luger, Rodrigo; Antonsen, Adrienne; Benedict, G. Fritz

    2015-05-01

    The ? Andromedae system is the first exoplanetary system to have the relative inclinations of two planets' orbital planes directly measured (McArthur et al. 2010), and therefore offers our first window into the 3-dimensional configurations of planetary systems. We present a full 3-dimensional, dynamically stable configuration for the 3 planets of the system, following up on McArthur et al (2010), which revealed that the orbits of the outer 2 planets are inclined by 30 deg. We used N-body simulations to search for stable 3-planet configurations that are consistent with the combined radial velocity and astrometric solution. The inner-most planet, b, could have only been detected by HST astrometry if it was at extremely low inclination. Because of this, its true mass and orbital plane are unconstrained by the observations, but our stability analysis limits their ranges significantly.The system appears to be close to the stability boundary, as we find that only 10 trials out of 1000 are robustly stable on 100 Myr timescales, or ~8 billion orbits of planet b. We find planet b's orbit must lie close to the fundamental plane of planets c and d, but can be either prograde or retrograde. These solutions predict b's mass is in the range 2 - 9 MJup and has an inclination angle from the sky plane of less than 45 deg. Crossfield et al. (2010) detected the planet via brightness variations in the combined light curve, and argued that such a configuration would require b's radius to be ~1.8 RJup, relatively large for a planet of its age. However, the eccentricity of b in several of our stable solutions reaches > 0.1, inducing upwards of 1019 watts in the interior of the planet via tidal dissipation. Ibgui et al. (2009) find that this energy source could inflate the radius to the amount required for Crossfield et al., and thus we have solutions that are consistent with all observational constraints.The Gaia telescope (Casertano et al. 2008) will refine the orbits of planets c and d and perhaps provide further constraints on b, such as a minimum inclination and maximum mass. Gaia will astrometrically determine the orbits of many other exoplanets, providing clues to the formation mechanisms and uniqueness of this system.

  7. Stable RNA interference rules for silencing

    PubMed Central

    Fellmann, Christof; Lowe, Scott W.

    2014-01-01

    RNA interference has become an indispensable tool for loss-of-function studies across eukaryotes. By enabling stable and reversible gene silencing, shRNAs provide a means to study long-term phenotypes, perform pool-based forward genetic screens and examine the consequences of temporary target inhibition in vivo. However, efficient implementation in vertebrate systems has been hindered by technical difficulties affecting potency and specificity. Focusing on these issues, we analyse current strategies to obtain maximal knockdown with minimal off-target effects. PMID:24366030

  8. Stable, Electroinactive Wetting Agent For Fuel Cells

    NASA Technical Reports Server (NTRS)

    Prakash, Surya G.; Olah, George A.; Narayanan, Sekharipuram R.; Surampudi, Subbarao; Halpert, Gerald

    1994-01-01

    Straight-chain perfluorooctanesulfonic acid (C8 acid) identified as innocuous and stable wetting agent for use with polytetrafluoroethylene-containing electrodes in liquid-feed direct-oxidation fuel cells suggested for use in vehicles and portable power supplies. C8 acid in small concentrations in aqueous liquid solutions of methanol, trimethoxymethane, dimethoxymethane, and trioxane enables oxidation of these substances by use of commercially available electrodes of type designed originally for use with gases. This function specific to C8 acid molecule and not achieved by other related perfluorolkanesulfonic acids.

  9. Rapid mixing renders quantum dissipative systems stable

    E-print Network

    Lucia, Angelo; Cubitt, Toby S.; Michalakis, Spyridon; Perez-Garcia, David

    2015-04-09

    Rapid mixing renders quantum dissipative systems stable Angelo Lucia,1 Toby S. Cubitt,2 Spyridon Michalakis,3 and David Pe´rez-Garc´?a1 1Dpto. Ana´lisis Matema´tico, Universidad Complutense de Madrid, 28040 Madrid, Spain 2DAMTP, University... , Nature Physics 8, 292 (2012). [14] I. Klich, Annals of Physics 325, 2120 (2010). [15] S. Bravyi, M. B. Hastings, and S. Michalakis, J. Math. Phys. 51, 093512 (2010), arXiv:1001.0344 [quant-ph]. [16] S. Michalakis and J. P. Zwolak, Commun. in Math. Phys...

  10. Shear viscosity of $?$-stable nuclear matter

    E-print Network

    Omar Benhar; Arianna Carbone

    2009-12-01

    Viscosity plays a critical role in determining the stability of rotating neutron stars. We report the results of a calculation of the shear viscosity of $\\beta$~-~stable matter, carried out using an effective interaction based on a state-of-the-art nucleon-nucleon potential and the formalism of correlated basis functions. Within our approach the equation of state, determining the proton fraction, and the nucleon-nucleon scattering probability are consistently obtained from the same dynamical model. The results show that, while the neutron contribution to the viscosity is always dominant, above nuclear saturation density the electron contribution becomes appreciable.

  11. Stable Feature Selection for Biomarker Discovery

    E-print Network

    He, Zengyou

    2010-01-01

    Feature selection techniques have been used as the workhorse in biomarker discovery applications for a long time. Surprisingly, the stability of feature selection with respect to sampling variations has long been under-considered. It is only until recently that this issue has received more and more attention. In this article, we review existing stable feature selection methods for biomarker discovery using a generic hierarchal framework. We have two objectives: (1) providing an overview on this new yet fast growing topic for a convenient reference; (2) categorizing existing methods under an expandable framework for future research and development.

  12. SINCERE STABLE TUBES I. REITEN AND A. SKOWRO '

    E-print Network

    Bielefeld, University of

    SINCERE STABLE TUBES I. REITEN AND A. SKOWRO ' NSKI Introduction The purpose of this paper with an identity) over an algebraically closed field k: If the AR­quiver of \\Lambda has a sincere family of stable. It is then a consequence that if the AR­quiver of \\Lambda has a sincere stable tube C such that there is no sequence X ! Y

  13. Perceptual Learning Immediately Yields New Stable Motor Coordination

    ERIC Educational Resources Information Center

    Wilson, Andrew D.; Snapp-Childs, Winona; Bingham, Geoffrey P.

    2010-01-01

    Coordinated rhythmic movement is specifically structured in humans. Movement at 0[degrees] mean relative phase is maximally stable, 180[degrees] is less stable, and other coordinations can, but must, be learned. Variations in perceptual ability play a key role in determining the observed stabilities so we investigated whether stable movements can…

  14. Local search algorithms on the Stable Marriage Problem: Experimental Studies

    E-print Network

    Rossi, Francesca

    Local search algorithms on the Stable Marriage Problem: Experimental Studies M. Gelain, M. S. Pini, F. Rossi, K. B. Venable 1 and T. Walsh 2 Abstract. The stable marriage problem (SM) has a wide a stable marriage: a matching of men to women with no blocking pair. A blocking pair consists of a man

  15. IS SOLAR SYSTEM STABLE? Vladik Kreinovich, Andrew Bernat

    E-print Network

    Kreinovich, Vladik

    IS SOLAR SYSTEM STABLE? A REMARK Vladik Kreinovich, Andrew Bernat Computer Science Department System is stable or not. Common belief is that the Solar System is stable if and only, a similar inequality is true for randomly chosen frequencies. In this paper, we show that the Solar system

  16. IS SOLAR SYSTEM STABLE? Vladik Kreinovich, Andrew Bernat

    E-print Network

    Kreinovich, Vladik

    IS SOLAR SYSTEM STABLE? A REMARK Vladik Kreinovich, Andrew Bernat Computer Science Department System is stable or not. Common belief is that the Solar System is stable if and only that the Solar system does not have such resonances, and therefore (if the above­mentioned belief is correct), we

  17. Stable Games Josef Hofbauer and William H. Sandholm

    E-print Network

    Hofbauer, Josef

    Stable Games Josef Hofbauer and William H. Sandholm Abstract-- We introduce a new class of population games called stable games. These games are characterized by self- defeating externalities: when are aban- doning. Stable games subsume many well-known classes of examples, including zero-sum games, games

  18. Population games, stable games, and passivity Michael J. Fox

    E-print Network

    Shamma, Jeff S.

    Population games, stable games, and passivity Michael J. Fox Jeff S. Shamma March 31, 2013 July 23, 2013 (revised) September 2, 2013 (revised) Abstract The class of "stable games", introduced by Hofbauer evolutionary dynamics. We show that stable games can be identified as a special case of the feedback

  19. Prediction of new thermodynamically stable aluminum oxides

    NASA Astrophysics Data System (ADS)

    Liu, Yue; Oganov, Artem R.; Wang, Shengnan; Zhu, Qiang; Dong, Xiao; Kresse, Georg

    2015-04-01

    Recently, it has been shown that under pressure, unexpected and counterintuitive chemical compounds become stable. Laser shock experiments (A. Rode, unpublished) on alumina (Al2O3) have shown non-equilibrium decomposition of alumina with the formation of free Al and a mysterious transparent phase. Inspired by these observations, we have explored the possibility of the formation of new chemical compounds in the system Al-O. Using the variable-composition structure prediction algorithm USPEX, in addition to the well-known Al2O3, we have found two extraordinary compounds Al4O7 and AlO2 to be thermodynamically stable in the pressure ranges 330-443 GPa and above 332 GPa, respectively. Both of these compounds at the same time contain oxide O2- and peroxide O22- ions, and both are insulating. Peroxo-groups are responsible for gap states, which significantly reduce the electronic band gap of both Al4O7 and AlO2.

  20. Protein-based stable isotope probing.

    PubMed

    Jehmlich, Nico; Schmidt, Frank; Taubert, Martin; Seifert, Jana; Bastida, Felipe; von Bergen, Martin; Richnow, Hans-Hermann; Vogt, Carsten

    2010-12-01

    We describe a stable isotope probing (SIP) technique that was developed to link microbe-specific metabolic function to phylogenetic information. Carbon ((13)C)- or nitrogen ((15)N)-labeled substrates (typically with >98% heavy label) were used in cultivation experiments and the heavy isotope incorporation into proteins (protein-SIP) on growth was determined. The amount of incorporation provides a measure for assimilation of a substrate, and the sequence information from peptide analysis obtained by mass spectrometry delivers phylogenetic information about the microorganisms responsible for the metabolism of the particular substrate. In this article, we provide guidelines for incubating microbial cultures with labeled substrates and a protocol for protein-SIP. The protocol guides readers through the proteomics pipeline, including protein extraction, gel-free and gel-based protein separation, the subsequent mass spectrometric analysis of peptides and the calculation of the incorporation of stable isotopes into peptides. Extraction of proteins and the mass fingerprint measurements of unlabeled and labeled fractions can be performed in 2-3 d. PMID:21127489

  1. Stable isotope enrichment using a plasma centrifuge

    NASA Astrophysics Data System (ADS)

    Krishnan, Mahadevan; Bures, Brian; Madden, Robert

    2012-10-01

    A primary goal of the Department of Energy's Isotope Development and Production for Research and Applications Program (Isotope Program) within the Office of Nuclear Physics (NP) is to produce isotopes that are in short supply in the U.S. and of which there exists no or insufficient domestic commercial production capability. A vacuum arc plasma centrifuge is a rigid rotor column of metal plasma in which centrifugal forces re-distribute ions radially according to their mass/charge ratio. Early work demonstrated rotation at 2 million rpm and separation of various stable isotopes. The spinning plasma column had a Gaussian flux profile, peaked on the rigid rotor axis. This work adopts a more efficient approach, with the plasma created as a hollow column, wherein the flux is concentrated at larger radii where the centrifugal action is highest. By tailoring the vacuum arc discharge geometry, the rotation rate can also be increased to ˜10 million rpm. Data from Cu, Al and other metal plasmas will be presented and discussed in light of enriched stable isotopes needed for research and medicine.

  2. Stable bubble oscillations beyond Blake's critical threshold.

    PubMed

    Heged?s, Ferenc

    2014-04-01

    The equilibrium radius of a single spherical bubble containing both non-condensable gas and vapor is determined by the mechanical balance at the bubble interface. This expression highlights the fact that decreasing the ambient pressure below the so called Blake's critical threshold, the bubble has no equilibrium state at all. In the last decade many authors have tried to find evidence for the existence of stable bubble oscillation under harmonic forcing in this regime, that is, they have tried to stabilize the bubble motion applying ultrasonic radiation on the bubble. The available numerical results provide only partial proof for the existence as they are usually based on linearized or weakly nonlinear (higher order approximation) bubble models. Here, based on numerical techniques of the modern nonlinear and bifurcation theory, the existence of stable bubble motion has been proven without any restrictions in nonlinearities. Although the model, applied in this paper, is the rather simple Rayleigh-Plesset equation, the presented technique can be extended to more complex bubble models easily. PMID:24485747

  3. N-heterocyclic carbene catalysis: expansion of 

    E-print Network

    Ogle, James William

    2009-05-15

    Asymmetric hydrogenation as a general route to polypropionates has been explored for allylic alcohols, acids, and derivatives, which has led to the generation of 2,4-dimethylated hexane derivatives. Quantitative yields in ...

  4. Carbene reactions produced by recoil excitation methods 

    E-print Network

    Lowery, Kirby

    1968-01-01

    by irradiation of samples in the presence of two competitors. Using ethylene as the standard in each case and using other olefins such as propylene, l-butene, isobutylene, cis-2-butene, and trans-2- butene, Tang and Rowland showed that the reactivity... Company in 99. 9! purity. The other gases used were obtained from The Matheson Company in research grade. Propane, isobutylene, methyl bromide, and methyl chloride had purity of greater than 99. 5X. Ethyl chloride, ethylene, isobutylene, pro- 13...

  5. N-heterocyclic carbene catalysis: expansion of

    E-print Network

    Ogle, James William

    2009-05-15

    .6.2 Noyori?s Catalysts???????????????????. 10 1.6.3 Pfaltz and Burgess? Catalyst???..??????????? 11 1.7 Further Studies?????????????????..??????. 13 CHAPTER II. SYNTHESIS OF POLYPROPIONATES USING ASYMMETRIC... Mycobacterium tuberculosis?.???..?? 7 Figure 1.4. Crabtree?s catalyst?????????????????????. 10 Figure 1.5. One of several of Noyori?s catalysts??????????????. 10 Figure 1.6. One of several of Pfaltz?s catalysts??????????????. 12 Figure 1.7. One...

  6. Carbene reactions produced by recoil excitation methods

    E-print Network

    Lowery, Kirby

    1968-01-01

    and CTCT. Reactions of CTF with 1, 3-butadiene, aliene, and cyclohexene were studied. Also, products of the Diels-Alder retrogression reaction of cyclohexene were observed when high energy tritium atoms reacted with cyclohexene. A qualitative discussion.... Experimental III. 'Reaction of Tritium-Labeled Monofluorocarbene with Higher Olefins 31 IV. Reactions of F -La'baled Monofluorocarbene V. Formation of Monochlorocarbene-Clgg VI. Formation of Monobromoc"rbene-Br VII. Diels-Alder Retrogression Reaction...

  7. Flag algebras and the stable coefficients of the Jones polynomial

    E-print Network

    Stavros Garoufalidis; Sergey Norin; Thao Vuong

    2015-04-22

    We study the structure of the stable coefficients of the Jones polynomial of an alternating link. We start by identifying the first four stable coefficients with polynomial invariants of a (reduced) Tait graph of the link projection. This leads us to introduce a free polynomial algebra of invariants of graphs whose elements give invariants of alternating links which strictly refine the first four stable coefficients. We conjecture that all stable coefficients are elements of this algebra, and give experimental evidence for the fifth and sixth stable coefficient. We illustrate our results in tables of all alternating links with at most 10 crossings and all irreducible planar graphs with at most 6 vertices.

  8. Transport of stable isotopes: I: Development of a kinetic continuum theory for stable isotope transport

    Microsoft Academic Search

    L. P. Baumgartner; D. Rumble

    1988-01-01

    Equations are developed describing migration of stable isotopes via a fluid phase infiltrating porous media. The formalism of continuum fluid mechanics is used to deal with the problem of microscopic inhomogeneity. Provision is made explicitly for local equilibrium exchange of isotopes between minerals and fluids as well as for kinetic control of isotopic exchange. Changing characteristic parameters of transport systems

  9. Isotropic turbulence, stable layers: atmospheric fictions

    NASA Astrophysics Data System (ADS)

    Lovejoy, S.; Tuck, A.; Hovde, S.; Schertzer, D.

    2007-12-01

    Using state of the art drop sonde data (from 237 sondes over the Pacific) we examine two classical and fundamental idealizations of atmospheric science showing that they are untenable in the light of the vertical structure. The first is the notion of stable atmospheric layers. This is used for understanding atmospheric dynamics and thermodynamics, including notions such as potential vorticity. Using the drop sonde data, we show that each apparently stable layer is actually composed of a hierarchy of unstable layers themselves with embedded stable sublayers, each with unstable sub-sub layers etc. i.e. in a Russian doll-like fractal hierarchy whose dimension we estimate. We therefore argue that the notion is untenable and must be replaced by modern scaling notions. Although the same basic conclusion follows for conditional, dynamical and convective stability, we showed that their correlation exponent (quantifying their sparsenesses) were 0.36±0.056, 0.22±0.037, 0.15±0.016 respectively. The second idealization we examine is the turbulence assumption of isotropy. If we include intermittency, Kolmorogov's landmark proposal that fully developed turbulence has an "inertial subrange" with isotropic energy spectrum E(k) ? k**-? with ??5/3 has apparently been spectacularly confirmed in both the horizontal direction and in the time domain (k is a wavenumber). For gradients over a horizontal distance ?x this implies ?v??z**Hh (Hh=1/3 corresponds to ?=5/3; "<.>" indicates ensemble averaging). Remarkably, Hv for gradients over vertical distances ?z (?v??z**Hv) has not been seriously investigated. Using drop sonde data of horizontal wind, we find that from scales of 5 m to >10 km from the surface layer through to the top of the troposphere, Hv is close to (or larger) than the Bolgiano-Obukhov value 3/5. Hv>Hh implies that a) the atmosphere becomes progressively less stratified at smaller scales although in a scaling way; b) that at most a single (roughly) isotropic "sphero-scale" exists (often in the range 1- 100 cm).

  10. Stable strontium isotope fractionation in synthetic barite

    NASA Astrophysics Data System (ADS)

    Widanagamage, Inoka H.; Schauble, Edwin A.; Scher, Howie D.; Griffith, Elizabeth M.

    2014-12-01

    The mineral barite (BaSO4) accommodates strontium (Sr) in its crystal structure, providing an archive of Sr-isotopes (87Sr/86Sr and ?88/86Sr) in the highly stable sulfate mineral. We investigated mass dependent stable Sr-isotope fractionation (?88/86Sr = ?88/86Srsolid - ?88/86Srsolution) during inorganic precipitation of barite from a barium-rich solution by addition of sulfate under controlled conditions and compared this to equilibrium isotopic fractionation calculated using Density Functional Theory modeling. Sr-substituted barite is predicted to have lower 88Sr/86Sr than any other studied species, and at 25 °C will be about 0.6-0.7‰ lower than the two modeled Sr(H2O)82+-bearing salts that could approximate aqueous Sr2+. This agrees in direction and order of magnitude with experimental results that estimate equilibrium Sr-isotope fractionation in barite to be 0.3‰ lower than aqueous Sr2+ at ?20 °C. The high ionic strength of some of the precipitating solutions (up to 1 M) and potential differences in the average coordination number of aqueous Sr2+ add to uncertainty in a direct comparison of the calculated equilibrium isotopic fractionation values with the experimental results. Stable Sr-isotope fractionation varied along with the distribution coefficient of Sr [Kd(Sr) = [Sr/Ba]barite/[Sr/Ba]solution], which is a function of both temperature and barite saturation state. However the relationship between mass dependent isotopic fractionation and Kd(Sr) is different for conditions of changing temperature versus barite saturation state. With increasing temperature (from 5 to 40 °C), the barite phase became isotopically lighter (?88/86Sr = -0.29‰ to -0.41‰). Conversely, with increasing saturation state (saturation index of barite = 3.0-4.3) the barite phase became isotopically heavier (?88/86Sr = -0.25‰ to -0.10‰). These observations suggest chemical kinetic effects control isotopic fractionation rather than equilibrium temperature effects. The relationship with saturation state indicates the potential presence of a diffusive boundary layer. Barite crystal morphology appears to be affected by the diffusion rate of solute (sulfate) to the growing crystal surface relative to the overall growth rate of barite crystals during precipitation.

  11. Modeling the dynamics of stable isotope tissue-diet enrichment.

    PubMed

    Remien, Christopher H

    2015-02-21

    Reconstructions of dietary composition and trophic level from stable isotope measurements of animal tissue rely on predictable offsets of stable isotope ratios from diet to tissue. Physiological processes associated with metabolism shape tissue stable isotope ratios, and as such the spacing between stable isotope ratios of diet and tissue may be influenced by processes such as growth, nutritional stress, and disease. Here, we develop a model of incorporation stable isotopes in diet to tissues by coupling stable isotope dynamics to a model of macronutrient energy metabolism. We use the model to explore the effect of changes in dietary intake, both composition and amount, and in energy expenditure, on body mass and carbon and nitrogen stable isotope ratios of tissue. PMID:25457228

  12. Molecular Structure of Dicarbon Monoxide

    NSDL National Science Digital Library

    2003-06-02

    Dicarbon monoxide is a carbonyl carbene (:C=C=O), a carbon with only two bonds and a pair of non-bonding electrons. These species are building blocks in the synthesis of organic compounds. When the divalent carbon is bonded to a metal, the carbene is more stable and plays an important role in organic synthesis.

  13. A stable phosphanyl phosphaketene and its reactivity.

    PubMed

    Li, Zhongshu; Chen, Xiaodan; Bergeler, Maike; Reiher, Markus; Su, Cheng-Yong; Grützmacher, Hansjörg

    2015-04-14

    Sodium phosphaethynolate, Na(OCP), reacts with the bulky P-chloro-diazaphosphole yielding a phosphanyl phosphaketene, which is stable for weeks under an inert atmosphere in the solid state. This compound is best described as a tight ion pair with a remarkably long P-P bond distance (2.44 Å). In solution, this phosphaketene dimerizes under loss of CO to give 1,2,3-triphosphabicyclobutane identified by an X-ray diffraction study. As an intermediate, a five-membered heterocyclic diphosphene was trapped in a Diels-Alder reaction with 2,3-dimethylbutadiene. The formation of this intermediate in a hetero-Cope-rearrangement as well as dimerization/CO loss were computed with various DFT methods which allowed us to understand the reaction mechanisms. PMID:25747929

  14. Towards stable silicon nanoarray hybrid solar cells

    NASA Astrophysics Data System (ADS)

    He, W. W.; Wu, K. J.; Wang, K.; Shi, T. F.; Wu, L.; Li, S. X.; Teng, D. Y.; Ye, C. H.

    2014-01-01

    Silicon nanoarray hybrid solar cells benefit from the ease of fabrication and the cost-effectiveness of the hybrid structure, and represent a new research focus towards the utilization of solar energy. However, hybrid solar cells composed of both inorganic and organic components suffer from the notorious stability issue, which has to be tackled before the hybrid solar cells could become a viable alternative for harvesting solar energy. Here we show that Si nanoarray/PEDOT:PSS hybrid solar cells with improved stability can be fabricated via eliminating the water inclusion in the initial formation of the heterojunction between Si nanoarray and PEDOT:PSS. The Si nanoarray hybrid solar cells are stable against rapid degradation in the atmosphere environment for several months without encapsulation. This finding paves the way towards the real-world applications of Si nanoarray hybrid solar cells.

  15. Development of stable lyophilized protein drug products.

    PubMed

    Remmele, Richard L; Krishnan, Sampathkumar; Callahan, William J

    2012-03-01

    Freeze drying, or lyophilization is widely used for biopharmaceuticals to improve the long term storage stability of labile molecules. This review examines general theory and practice of rational lyophilization of biopharmaceuticals. Formulation development involving the selection of appropriate excipients, their associated physical properties, and mechanism of action in achieving a stable drug product are primary considerations for a successful lyophilization program. There are several parameters considered critical on the basis of their relationship to lyophilization cycle development and protein product stability. This along with the importance of analytical methods to provide insight toward understanding properties of drug product stability and cake structure are discussed. Also, aspects of instability found in lyophilized biopharmaceutical products, their degradation pathways and control are elucidated. Finally, container-closure requirements and drug product handling are described in context of the caveats to avoid compromising drug product quality. PMID:22283723

  16. Modelling of the Evolving Stable Boundary Layer

    NASA Astrophysics Data System (ADS)

    Sorbjan, Zbigniew

    2014-06-01

    A single-column model of the evolving stable boundary layer (SBL) is tested for self-similar properties of the flow and effects of ambient forcing. The turbulence closure of the model is diagnostic, based on the K-theory approach, with a semi-empirical form of the mixing length, and empirical stability functions of the Richardson number. The model results, expressed in terms of local similarity scales, are universal functions, satisfied in the entire SBL. Based on similarity expression, a realizability condition is derived for the minimum allowable turbulent heat flux in the SBL. Numerical experiments show that the development of "horse-shoe" shaped, fixed-elevation hodographs in the interior of the SBL around sunrise is controlled by effects imposed by surface thermal forcing.

  17. Coil bobbin for stable superconducting coils

    SciTech Connect

    Kashima, T.; Yamanaka, A. [Toyobo Co., Ltd, Ohtsu, Shiga (Japan); Nishijima, S.; Okada, T. [Osaka Univ., Ibaraki (Japan)] [and others

    1996-12-31

    The coil bobbin for a.c. coils have been prepared with the high strength polyethylene fiber (DF) reinforced plastics (DFRP) or with hybrid composites reinforced by DF and glass fiber (GF). The coils with the bobbin were found to be markedly stable. The DF has a large negative thermal expansion coefficient and hence the circumferential thermal strain of bobbin can be designed by changing the ratio of DF to GF layer thickness (DF/GF). It was found that the thermal expansion coefficient in the circumferential direction of the outer surface changed from negative to positive with increasing DF/GF and became nearly zero at a DF/GF of approximately 5.1 kA rms class a.c. coils having a bobbin with a negative thermal expansion coefficient or small thermal contraction in the circumferential direction were fabricated and were confirmed to show higher quench current than that with a GFRP bobbin.

  18. Stable Xenon Nitride at High Pressures

    NASA Astrophysics Data System (ADS)

    Zhang, Yunwei; Peng, Feng; Ma, Yanming

    2015-03-01

    Nitrogen is the most abundant element on Earth and exists as inert N2 molecules in the atmosphere. Noble gas nitrides are missing in nature because N2 molecules do not interact with noble gases at ambient conditions, greatly impeding the understanding of physics and chemistry of such nitrides. We report here a pressure-induced chemical reaction of N2 with xenon predicted using a swarm-structure searching calculation as implemented in the CALYPSO code. This reaction leads to the formation of a hitherto unexpected Xe nitride at megabar pressure accessible to high-pressure experiments. The high-pressure phase with a hypervalent state of Xe by accepting unprecedented Xe-N covalent bonds appears to be the most stable stoichiometry. The Xe bonding situation in this new phase is substantially different from earlier high-pressure examples of ionic Xe bonding or van der Waals interactions.

  19. Measuring In Vivo Ureagenesis With Stable Isotopes

    PubMed Central

    Yudkoff, Marc; Mew, Nicholas Ah; Daikhin, Yevgeny; Horyn, Oksana; Nissim, Ilana; Nissim, Itzhak; Payan, Irma; Tuchman, Mendel

    2010-01-01

    Stable isotopes have been an invaluable adjunct to biomedical research for more than 70 years. Indeed, the isotopic approach has revolutionized our understanding of metabolism, revealing it to be an intensely dynamic process characterized by an unending cycle of synthesis and degradation. Isotopic studies have taught us that the urea cycle is intrinsic to such dynamism, since it affords a capacious mechanism by which to eliminate waste nitrogen when rates of protein degradation (or dietary protein intake) are especially high. Isotopes have enabled an appreciation of the degree to which ureagenesis is compromised in patients with urea cycle defects. Indeed, isotopic studies of urea cycle flux correlate well with the severity of cognitive impairment in these patients. Finally, the use of isotopes affords an ideal tool with which to gauge the efficacy of therapeutic interventions to augment residual flux through the cycle. PMID:20338795

  20. Ultra-stable oscillator with complementary transistors

    NASA Technical Reports Server (NTRS)

    Kleinberg, L. L. (inventor)

    1974-01-01

    A high frequency oscillator, having both good short and long term stability, is formed by including a piezoelectric crystal in the base circuit of a first bi-polar transistor circuit, the bi-polar transistor itself operated below its transitional frequency and having its emitter load chosen so that the input impedance, looking into the base thereof, exhibits a negative resistance in parallel with a capacitive reactance. Combined with this basic circuit is an auxiliary, complementary, second bi-polar transistor circuit of the same form with the piezoelectric crystal being common to both circuits. By this configuration small changes in quiescent current are substantially cancelled by opposite variations in the second bi-polar transistor circuit, thereby achieving from the oscillator a signal having its frequency of oscillation stable over long time periods as well as short time periods.

  1. Bounded excursion stable gravastars and black holes

    SciTech Connect

    Rocha, P [Instituto de Fisica, Universidade Federal Fluminense, Avenida Litoranea, s/n, Boa Viagem 24210-340, Niteroi, RJ (Brazil)] [Instituto de Fisica, Universidade Federal Fluminense, Avenida Litoranea, s/n, Boa Viagem 24210-340, Niteroi, RJ (Brazil); Miguelote, A Y; Chan, R [Coordenacao de Astronomia e Astrofisica, Observatorio Nacional, Rua General Jose Cristino, 77, Sao Cristovao 20921-400, Rio de Janeiro, RJ (Brazil)] [Coordenacao de Astronomia e Astrofisica, Observatorio Nacional, Rua General Jose Cristino, 77, Sao Cristovao 20921-400, Rio de Janeiro, RJ (Brazil); Da Silva, M F; Wang, Anzhong [Departamento de Fisica Teorica, Instituto de Fisica, Universidade do Estado do Rio de Janeiro, Rua Sao Francisco Xavier 524, Maracana 20550-900, Rio de Janeiro-RJ (Brazil)] [Departamento de Fisica Teorica, Instituto de Fisica, Universidade do Estado do Rio de Janeiro, Rua Sao Francisco Xavier 524, Maracana 20550-900, Rio de Janeiro-RJ (Brazil); Santos, N O, E-mail: pedrosennarocha@gmail.com, E-mail: yasuda@on.br, E-mail: chan@on.br, E-mail: mfasnic@gmail.com, E-mail: N.O.Santos@qmul.ac.uk, E-mail: anzhong_wang@baylor.edu [LERMA/CNRS-FRE 2460, Universite Pierre et Marie Curie, ERGA, Boite 142, 4 Place Jussieu, 75005 Paris Cedex 05 (France)

    2008-06-15

    Dynamical models of prototype gravastars were constructed in order to study their stability. The models are the Visser-Wiltshire three-layer gravastars, in which an infinitely thin spherical shell of stiff fluid divides the whole spacetime into two regions, where the internal region is de Sitter, and the external one is Schwarzschild. It is found that in some cases the models represent the 'bounded excursion' stable gravastars, where the thin shell is oscillating between two finite radii, while in other cases they collapse until the formation of black holes occurs. In the phase space, the region for the 'bounded excursion' gravastars is very small in comparison to that of black holes, but not empty. Therefore, although the possibility of the existence of gravastars cannot be excluded from such dynamical models, our results indicate that, even if gravastars do indeed exist, that does not exclude the possibility of the existence of black holes.

  2. Evolutionarily stable sex ratios and mutation load.

    PubMed

    Hough, Josh; Immler, Simone; Barrett, Spencer C H; Otto, Sarah P

    2013-07-01

    Frequency-dependent selection should drive dioecious populations toward a 1:1 sex ratio, but biased sex ratios are widespread, especially among plants with sex chromosomes. Here, we develop population genetic models to investigate the relationships between evolutionarily stable sex ratios, haploid selection, and deleterious mutation load. We confirm that when haploid selection acts only on the relative fitness of X- and Y-bearing pollen and the sex ratio is controlled by the maternal genotype, seed sex ratios evolve toward 1:1. When we also consider haploid selection acting on deleterious mutations, however, we find that biased sex ratios can be stably maintained, reflecting a balance between the advantages of purging deleterious mutations via haploid selection, and the disadvantages of haploid selection on the sex ratio. Our results provide a plausible evolutionary explanation for biased sex ratios in dioecious plants, given the extensive gene expression that occurs across plant genomes at the haploid stage. PMID:23815649

  3. Towards stable silicon nanoarray hybrid solar cells

    PubMed Central

    He, W. W.; Wu, K. J.; Wang, K.; Shi, T. F.; Wu, L.; Li, S. X.; Teng, D. Y.; Ye, C. H.

    2014-01-01

    Silicon nanoarray hybrid solar cells benefit from the ease of fabrication and the cost-effectiveness of the hybrid structure, and represent a new research focus towards the utilization of solar energy. However, hybrid solar cells composed of both inorganic and organic components suffer from the notorious stability issue, which has to be tackled before the hybrid solar cells could become a viable alternative for harvesting solar energy. Here we show that Si nanoarray/PEDOT:PSS hybrid solar cells with improved stability can be fabricated via eliminating the water inclusion in the initial formation of the heterojunction between Si nanoarray and PEDOT:PSS. The Si nanoarray hybrid solar cells are stable against rapid degradation in the atmosphere environment for several months without encapsulation. This finding paves the way towards the real-world applications of Si nanoarray hybrid solar cells. PMID:24430057

  4. Stable homotopical algebra and [Gamma]-spaces

    NASA Astrophysics Data System (ADS)

    Schwede, Stefan

    1999-03-01

    In this paper we advertise the category of [Gamma]-spaces as a convenient framework for doing ‘algebra’ over ‘rings’ in stable homotopy theory. [Gamma]-spaces were introduced by Segal [Se] who showed that they give rise to a homotopy category equivalent to the usual homotopy category of connective (i.e. ([minus sign]1)-connected) spectra. Bousfield and Friedlander [BF] later provided model category structures for [Gamma]-spaces. The study of ‘rings, modules and algebras’ based on [Gamma]-spaces became possible when Lydakis [Ly] introduced a symmetric monoidal smash product with good homotopical properties. Here we develop model category structures for modules and algebras, set up (derived) smash products and associated spectral sequences and compare simplicial modules and algebras to their Eilenberg-MacLane spectra counterparts.

  5. Metabolically stable cellular adhesion to inert surfaces.

    PubMed

    Meldal, Morten; Wu, Boqian; Diness, Frederik; Michael, Roice; Hagel, Grith

    2011-11-01

    The structure of D-amino acid hexapeptides that promote cellular adhesion was determined by screening D-amino acid hexapeptide libraries synthesized on otherwise inert beaded PEGA resin. These new adhesion molecules provide a completely stable cellular environment and facilitate the maintenance of a monolayer of cells on beads for extended periods. The presence of the peptides promotes spreading of the cells on the bead surface. Not surprisingly, the molecules contained a significant number of arginines and/or lysines. However, the exact structure of each peptide is quite important for the degree of adhesion observed, and a motif with three or four basic amino acids spaced within amino acids of intermediate polarity clearly prevailed, for example, k-l/r-h-r-i/v-r-a; this maintains a polar/hydrophobic balance. PMID:21928441

  6. Evolutionarily stable and convergent stable strategies in reaction-diffusion models for conditional dispersal.

    PubMed

    Lam, King-Yeung; Lou, Yuan

    2014-02-01

    We consider a mathematical model of two competing species for the evolution of conditional dispersal in a spatially varying, but temporally constant environment. Two species are different only in their dispersal strategies, which are a combination of random dispersal and biased movement upward along the resource gradient. In the absence of biased movement or advection, Hastings showed that the mutant can invade when rare if and only if it has smaller random dispersal rate than the resident. When there is a small amount of biased movement or advection, we show that there is a positive random dispersal rate that is both locally evolutionarily stable and convergent stable. Our analysis of the model suggests that a balanced combination of random and biased movement might be a better habitat selection strategy for populations. PMID:24430731

  7. Application of Stable Isotope Tracers to Determine Latent Heat Exchange in Stable and Condensing Boundary Layers

    NASA Astrophysics Data System (ADS)

    Noone, D. C.; Raudzens Bailey, A.; Berkelhammer, M. B.; Cox, C.; Kaushik, A.

    2014-12-01

    Understanding the manner in which material is exchanged between the planetary boundary layer and the free troposphere is essential for evaluating many aspects of climate, including the distribution of trace gases, the transport of energy and water, cloud types, climate sensitivity, and the surface energy balance. However, neither observations nor parameterized numerical models constrain the interplay between moist processes and joint exchanges of water and heat adequately. Advance in understanding is limited in part by the complex controls on turbulence and, in the case of cloudy boundary layers, the interplay between turbulent mixing and latent heating, which is difficult to observe. Recent theoretical and observational advances now allow stable isotope ratios of water vapor and cloud condensate to be used to isolate the transport component from other thermodynamic controls, including condensation. Here we expose the role of latent heat exchanges that would be difficult to determine without a method to track water vapor transport. Analysis of case of a very stable boundary layer shows sustained downward latent heat fluxes during the development of a radiative inversion, and which establishes a new basis for parameterizing turbulence under stable conditions. The case of a capped convective marine boundary layer highlights the role of transport processes and condensation, which are critical for maintaining the temperature and humidity structure of the lower atmosphere over tropical oceans. While a variety of trace gases can be used to identify air mass exchange, water stable isotope ratios are particularly useful because they can identify latent heat exchanges, which are necessary to fully account for the coupling of water and energy in the boundary layer. The use of isotopic tracers explicitly captures this coupling even in the case of weak turbulence when important terms needed to resolve the local energy balance would otherwise be lost.

  8. Three new stable L5 Mars Trojans

    NASA Astrophysics Data System (ADS)

    de la Fuente Marcos, C.; de la Fuente Marcos, R.

    2013-05-01

    Mars was second to Jupiter in being recognized as the host of a population of Trojan minor bodies. Since 1990, five asteroids - 5261 Eureka, (101429) 1998 VF31, (121514) 1999 UJ7, 2001 DH47 and (311999) 2007 NS2 - have been identified as Mars Trojans, one L4 and four L5. Dynamical and spectroscopic evidence suggests that some Mars Trojans may be remnants of the original planetesimal population that formed in the terrestrial planets region. Here, we revisit the long-term dynamical evolution of the previously known Mars Trojans and show that 2011 SC191, 2011 SL25 and 2011 UN63 are also trailing (L5) Mars Trojans. They appear to be as stable as Eureka and may have been Trojans over the age of the Solar system. The fact that five Trojans move in similar orbits and one of them is a binary may point to the disruption of a larger body early in the history of the Solar system. Such a catastrophic event may also explain the apparently strong asymmetry in terms of number of objects (one versus seven) between the L4 and L5 regions. Future spectroscopic observations should be able to reject or confirm a putative common chemical signature that may lend further support to a collisional scenario.

  9. How stable is the Mississippi Delta?

    NASA Astrophysics Data System (ADS)

    Törnqvist, Torbjörn E.; Bick, Scott J.; van der Borg, Klaas; de Jong, Arie F. M.

    2006-08-01

    Large deltas are commonly believed to exhibit rapid rates of tectonic subsidence, largely due to sediment loading of the lithosphere. As a result, deltaic plains are prone to accelerated relative sea-level rise, coastal erosion, and wetland loss. Hurricane Katrina's devastation testifies to the severe threat that these processes pose to the Mississippi Delta, but the relative role of tectonics versus other mechanisms causing land subsidence remains elusive. Relative sea-level records derived from basal peat have the potential to quantify differential crustal movements over Holocene time scales with exceptionally high accuracy and precision. Here we present new sea-level index points from two study areas in the southwestern Mississippi Delta that essentially coincide with a recently published detailed relative sea-level record from the eastern part of the delta. Our results show that differential vertical movements among the three study areas have been only ˜0.1 mm yr-1. We compare our evidence with a recent sea-level compilation from the Caribbean, to a large extent based on data from areas that are tectonically stable. Our sea-level index points nearly coincide with the Caribbean data, showing surprising tectonic stability for considerable sections of the Mississippi Delta. However, the well-documented high subsidence rates in and near the birdfoot of the Mississippi Delta indicate that different conditions prevail there. The rapid wetland loss in coastal Louisiana is likely due, to a considerable extent, to the compaction of Holocene strata.

  10. Resistance management: the stable zone strategy

    PubMed Central

    Lenormand, T.; Raymond, M.

    1998-01-01

    The different strategies of insecticide resistance management that have been formulated so far consist of delaying the appearance and spread of resistance genes. In this paper, we propose a strategy that can be used even if resistance genes are already present. This strategy consists of applying insecticides in an area smaller than a certain critical size, so that gene flow from the untreated area, combined with the fitness cost of the resistance genes, prevents its frequency reaching high equilibrium value. A two-locus model was analysed numerically to determine population densities at equilibrium as a function of selection coefficients (insecticide selection, fitness costs of resistance genes and dominances), gene flow and size of the treated area. This model indicates that there is an optimal size for the treated area where a minimal and stable density reach equilibrium, and where resistance genes cannot invade. This resistance management strategy seems applicable to a large variety of field situations, but eventually it may encounter obstacles due to a modifier which reduces the fitness costs of resistance genes.

  11. Magneto-hydrodynamically stable axisymmetric mirrors

    SciTech Connect

    Ryutov, D. D.; Cohen, B. I.; Molvik, A. W. [Lawrence Livermore National Laboratory, Livermore, California 94551 (United States); Berk, H. L. [University of Texas, Austin, Texas 78712 (United States); Simonen, T. C. [University of California, Berkeley, California 94720 (United States)

    2011-09-15

    Making axisymmetric mirrors magnetohydrodynamically (MHD) stable opens up exciting opportunities for using mirror devices as neutron sources, fusion-fission hybrids, and pure-fusion reactors. This is also of interest from a general physics standpoint (as it seemingly contradicts well-established criteria of curvature-driven instabilities). The axial symmetry allows for much simpler and more reliable designs of mirror-based fusion facilities than the well-known quadrupole mirror configurations. In this tutorial, after a summary of classical results, several techniques for achieving MHD stabilization of the axisymmetric mirrors are considered, in particular: (1) employing the favorable field-line curvature in the end tanks; (2) using the line-tying effect; (3) controlling the radial potential distribution; (4) imposing a divertor configuration on the solenoidal magnetic field; and (5) affecting the plasma dynamics by the ponderomotive force. Some illuminative theoretical approaches for understanding axisymmetric mirror stability are described. The applicability of the various stabilization techniques to axisymmetric mirrors as neutron sources, hybrids, and pure-fusion reactors are discussed; and the constraints on the plasma parameters are formulated.

  12. Magneto-hydrodynamically stable axisymmetric mirrorsa)

    NASA Astrophysics Data System (ADS)

    Ryutov, D. D.; Berk, H. L.; Cohen, B. I.; Molvik, A. W.; Simonen, T. C.

    2011-09-01

    Making axisymmetric mirrors magnetohydrodynamically (MHD) stable opens up exciting opportunities for using mirror devices as neutron sources, fusion-fission hybrids, and pure-fusion reactors. This is also of interest from a general physics standpoint (as it seemingly contradicts well-established criteria of curvature-driven instabilities). The axial symmetry allows for much simpler and more reliable designs of mirror-based fusion facilities than the well-known quadrupole mirror configurations. In this tutorial, after a summary of classical results, several techniques for achieving MHD stabilization of the axisymmetric mirrors are considered, in particular: (1) employing the favorable field-line curvature in the end tanks; (2) using the line-tying effect; (3) controlling the radial potential distribution; (4) imposing a divertor configuration on the solenoidal magnetic field; and (5) affecting the plasma dynamics by the ponderomotive force. Some illuminative theoretical approaches for understanding axisymmetric mirror stability are described. The applicability of the various stabilization techniques to axisymmetric mirrors as neutron sources, hybrids, and pure-fusion reactors are discussed; and the constraints on the plasma parameters are formulated.

  13. Minute synthesis of extremely stable gold nanoparticles

    NASA Astrophysics Data System (ADS)

    Zhou, Min; Wang, Baoxiang; Rozynek, Zbigniew; Xie, Zhaohui; Fossum, Jon Otto; Yu, Xiaofeng; Raaen, Steinar

    2009-12-01

    We describe a rapid environmentally friendly wet-chemical approach to synthesize extremely stable non-toxic, biocompatible, water-soluble monodispersed gold nanoparticles (AuNPs) in one step at room temperature. The particles have been successfully achieved in just a few minutes by merely adding sodium hydroxide (NaOH) acting as an initiator for the reduction of HAuCl4 in aqueous solution in the presence of polyvinylpyrrolidone (PVP) without the use of any reducing agent. It is also proved to be highly efficient for the preparation of AuNPs with controllable sizes. The AuNPs show remarkable stability in water media with high concentrations of salt, various buffer solutions and physiological conditions in biotechnology and biomedicine. Moreover, the AuNPs are also non-toxic at high concentration (100 µM). Therefore, it provides great opportunities to use these AuNPs for biotechnology and biomedicine. This new approach also involved several green chemistry concepts, such as the selection of environmentally benign reagents and solvents, without energy consumption, and less reaction time.

  14. Stable isotopic characterisation of francolite formation

    NASA Astrophysics Data System (ADS)

    McArthur, J. M.; Benmore, R. A.; Coleman, M. L.; Soldi, C.; Yeh, H.-W.; O'Brien, G. W.

    1986-02-01

    Stable isotopic data are presented for 112 samples of francolite from 18 separate phosphate deposits. Values of ? 13C and ? 34S in most offshore deposits suggest formation within oxic or suboxic environments either by carbonate replacement or direct precipitation of francolite from water of normal marine compositions. The exceptions are concretionary francolite from Namibia, which has an isotopic composition in keeping with its formation within organic-rich sediments, and that from offshore Morocco, which has an isotopic signature of the anoxic/suboxic interface. Onshore deposits from Jordan, Mexico, South Africa and, possibly, the Permian Phosphoria Formation in the western U.S.A., are substantially depleted in 18O: they appear to be too altered for deductions to be made about their environments of formation. In other onshore deposits which are unaltered, or minimally altered, the isotopic composition suggests that some formed within sulphate-reducing sediments (Sedhura, Morocco) whilst francolite from the Georgina Basin of Australia formed at the oxic/anoxic boundary, where oxidation of biogenic H 2S decreases the ? 34S of pore water. In general, pelletal samples show non-oxic isotopic signatures, whilst non-pelletal samples show oxic isotopic signatures, but samples from Namibia, Peru (Ica Plateau) and the Californian and Moroccan margins are exceptions to this rule. Morphology may therefore be a misleading indicator of francolite genesis as no definitive relation exists between phosphorite type and isotopic signature.

  15. Interpreting stable and unstable ecosystem model behaviour

    NASA Astrophysics Data System (ADS)

    Pietsch, S. A.

    2009-04-01

    Large-scale ecosystem models describe the fluxes of energy and matter within terrestrial ecosystem, using mechanistic descriptions of ecosystem processes such as photosynthesis, decomposition, mineralization, transpiration, evaporation, net primary production or net ecosystem carbon exchange. Currently, this type of ecosystem models is the main tool for analysing the carbon balance of terrestrial ecosystem under scenarios of climate change. In this paper model simulations for three different ecosystems (Scots pine, Cembran pine and Common beech forest ecosystems) are analysed using the attractors of model behaviour, which are reconstructed from quasi-periodic model outputs. Stable and unstable attractor configurations are discussed according to (i) their ecological interpretation and (ii) the implications of the respective attractor configurations on predictive power of model outputs. The results show that large-scale ecosystem models may be used to: (i) determine the amount of information needed to model ecosystem behaviour, (ii) estimate the current resilience status of the modelled ecosystem, and (iii) detect situations where model application delivers meaningless results.

  16. Stable carbon isotope analysis of coprocessing materials

    SciTech Connect

    Lancet, M.S.; Winschel, R.A.; Burke, F.P.

    1991-02-01

    Consol R D is developing and demonstrating stable carbon isotope analysis as a method to quantitatively distinguish coal-derived and petroleum-derived carbon in products from coal/petroleum coprocessing. The approach taken is develop the method, then demonstrate its application on authentic continuous-unit products. The significance of selective isotopic fractionation is being determined and, when necessary, corrections are applied to account for it. Precision, accuracy and range of applicability are being defined. The value of accessory analytical techniques also is being assessed. Previously reported data on samples from HRI bench-scale coprocessing Runs 227-53 (Texas lignite/Maya ASB and Texas lignite/Maya VSB) and 238-1 (Westerholt coal/Cold Lake VSB) were corrected for selective isotopic fractionation. Carbon sourcing was performed on samples from HRI bench-scale coprocessing Run 227-60 (Texas lignite/Maya VSB) and samples from UOP bench-scale coprocessing Run 26 (Illinois 6 coal/Lloydminster vacuum resid); the latter data were corrected for isotopic fractionation, though the former could not be corrected. A paper presented at the 1990 DOE Direct Liquefaction Contractor's Review Meeting is appended. 15 refs., 21 figs., 22 tabs.

  17. The Stable K0 Giant Star ? Gem

    NASA Astrophysics Data System (ADS)

    Gray, David F.

    2014-12-01

    A nine-season spectroscopic study of the photosphere of ? Gem (K0 III) shows this low-luminosity giant to be stable, with no effective temperature variations above ~2 K, and no secular temperature variations over the 2002-2010 time span above 0.2 K per year. The radial-velocity variations are consistent with an orbital variation of ~40 m s-1. The projected rotation rate is found to be 1.70 ± 0.20 km s-1 with a macroturbulence dispersion of 4.53 ± 0.10 km s-1. The third-signature plot is also invariant and shows a granulation velocity gradient 20% smaller than the solar gradient. The absolute shift of the third-signature plot gives a blueshift-corrected radial velocity of 3385 ± 70 m s-1. Bisector mapping of the Fe I ?6253 line yields a flux deficit of 12% ± 1% in area, somewhat smaller than for other giants, but the shape and the position of the peak at 4.8 km s-1 is consistent with other giants. All of the investigated photospheric parameters are consistent with ? Gem being a low-luminosity giant in agreement with its absolute magnitude.

  18. Organized polysaccharide fibers as stable drug carriers

    PubMed Central

    Janaswamy, Srinivas; Gill, Kristin L.; Campanella, Osvaldo H.; Pinal, Rodolfo

    2013-01-01

    Many challenges arise during the development of new drug carrier systems, and paramount among them are safety, solubility and controlled release requirements. Although synthetic polymers are effective, the possibility of side effects imposes restrictions on their acceptable use and dose limits. Thus, a new drug carrier system that is safe to handle and free from side effects is very much in need and food grade polysaccharides stand tall as worthy alternatives. Herein, we demonstrate for the first time the feasibility of sodium iota-carrageenan fibers and their distinctive water pockets to embed and release a wide variety of drug molecules. Structural analysis has revealed the existence of crystalline network in the fibers even after encapsulating the drug molecules, and iota-carrageenan maintains its characteristic and reproducible double helical structure suggesting that the composites thus produced are reminiscent of cocrystals. The melting properties of iota-carrageenan:drug complexes are distinctly different from those of either drug or iota-carrageenan fiber. The encapsulated drugs are released in a sustained manner from the fiber matrix. Overall, our research provides an elegant opportunity for developing effective drug carriers with stable network toward enhancing and/or controlling bioavailability and extending shelf-life of drug molecules using GRAS excipients, food polysaccharides, that are inexpensive and non–toxic. PMID:23544530

  19. Stable ETL Optimal Portfolios and Extreme Risk Management

    Microsoft Academic Search

    Svetlozar T. Rachev; R. Douglas Martin; Borjana Racheva; Stoyan Stoyanov

    We introduce a practical alternative to Gaussian risk factor distributions based on Svetlozar Rachev's work on Stable Paretian Models in Finance (see [4]) and called the Stable Distribution Framework. In contrast to normal distributions, stable distributions capture\\u000a the fat tails and the asymmetries of real-world risk factor distributions. In addition, we make use of copulas, a generalization\\u000a of overly restrictive

  20. Complexity of the sex-equal stable marriage problem

    Microsoft Academic Search

    Akiko Kato

    1993-01-01

    A stable marriage problem of sizen involvesn men andn women each with a strict preference ordering over all the members of the opposite sex. A solution, called a stable matching,\\u000a matches the men and women so that no man and woman both prefer each other to their respective partners. The sex-equal stable\\u000a marriage problem posed by Gusfield and Irving [5

  1. Stable SU(5) monopoles with higher magnetic charge

    SciTech Connect

    Miyamoto, S.; Sato, H.; Tomohiro, S.

    1985-09-15

    Taking into account the electroweak breaking effects, some multiply charged monopoles were shown to be stable by Gardner and Harvey. We give the explicit Ansa$uml: tze for finite-energy, nonsingular solutions of these stable higher-strength monopoles with eg = 1,(3/2),3. We also give the general stability conditions and the detailed behavior of the interaction potentials between two monopoles which produce the stable higher-strength monopoles.

  2. HUNT STABLE COMPLEX LOOKING NORTHWEST TOWARD DOG KENNEL RUINS ACROSS ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    HUNT STABLE COMPLEX LOOKING NORTHWEST TOWARD DOG KENNEL RUINS ACROSS THE GREAT CIRCUS - Overhills, Fort Bragg Military Reservation, Approximately 15 miles NW of Fayetteville, Overhills, Harnett County, NC

  3. Magneto-hydrodynamically stable axisymmetric mirrors

    NASA Astrophysics Data System (ADS)

    Ryutov, Dmitri

    2010-11-01

    The achievement of high beta (60%) plasma with near classical confinement in a linear axisymmetric magnetic configuration has sparked interest in the Gas Dynamic Trap concept. The significance of these results is that they can be projected directly to a neutron source for materials testing. The possibility of axisymmetric mirrors (AM) being magneto-hydrodynamically (MHD) stable is also of interest from a general physics standpoint (as it seemingly contradicts to well-established criteria of curvature-driven instabilities). The axial symmetry allows for much simpler and more reliable designs of mirror-based fusion facilities than the well-known quadrupole mirror configurations. In this tutorial, after a brief summary of classical results (in particular of the Rosenbluth-Longmire theory and of the energy principle as applied to AM) several approaches towards achieving MHD stabilization of the AM will be considered: 1) Employing the favorable field-line curvature in the end tanks; 2) Using the line-tying effect; 3) Setting the plasma in a slow or fast differential rotation; 4) Imposing a divertor configuration on the solenoidal magnetic field; 5) Controlling the plasma dynamics by the ponderomotive force; 6) Other techniques. Several of these approaches go beyond pure MHD and require accounting for finite Larmor radius effects and trapped particle modes. Some illuminative theoretical approaches for understanding axisymmetric mirror stability will be described. Wherever possible comparison of theoretical and experimental results on AM will be provided. The applicability of the various stabilization techniques to axisymmetric mirrors as neutron sources, hybrids, and pure-fusion reactors will be discussed and the constraints on the plasma parameters will be formulated. Prepared by LLNL under Contract DE-AC52-07NA27344.

  4. Problem Tools The censored process Results Censored stable processes

    E-print Network

    Problem Tools The censored process Results Censored stable processes Andreas E. Kyprianou1 Juan-Carlos Pardo2 Alex Watson1 1 Unversity of Bath, UK. 2 CIMAT, Mexico. #12;Problem Tools The censored process(Xt 0) will frequently appear as will ^ = 1 - . #12;Problem Tools The censored process Results Stable

  5. STABLE STATE OF INTERCONNECT UNDER TEMPERATURE CHANGE AND ELECTRIC CURRENT

    E-print Network

    Suo, Zhigang

    STABLE STATE OF INTERCONNECT UNDER TEMPERATURE CHANGE AND ELECTRIC CURRENT Z. SUO Mechanical electric current, such an interconnect evolvesÐafter a compli- cated sequence of eventsÐinto a stable state, and no further mass diusion. The electric current continues in the shunt layers where aluminum is depleted

  6. Compact Preference Representation in Stable Marriage Enrico Pilotto1

    E-print Network

    Walsh, Toby

    applications. It is usually defined as the problem of matching men to women so that no man and woman, who sailors to ships in the US Navy. Surprisingly, a stable matching always exists whatever preferences are held by the men and women. The Gale-Shapley algorithm finds a stable matching in polynomial time [4

  7. Compact preference representation in stable marriage E. Pilotto1

    E-print Network

    Rossi, Francesca

    applications. It is usually defined as the problem of matching men to women so that no man and woman, who sailors to ships in the US Navy. Surprisingly, a stable matching always exists whatever preferences are held by the men and women. The Gale-Shapley algorithm finds a stable matching in polynomial time [4

  8. MINERAL BIOAVAILABILITY AND METABOLISM DETERMINED BY USING STABLE ISOTOPE TRACERS

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Definitive data on mineral bioavailability in humans and animals can be obtained by using isotopic tracers. The use of stable isotope tracers to study important issues in mineral nutrition has expanded rapidly in the past two decades, particularly in humans. Stable isotopes have a number of advanta...

  9. Stable fly control in cattle winter feeding sites with Novaluron

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The mixture of wasted feed with manure and urine residues at livestock winter feeding sites provides an excellent substrate for the development of immature stable flies, Stomoxys calcitrans (L.). Such sites are primary sources of early summer stable flies in the central United States and limited opt...

  10. Alpha-Stable Distributions in Signal Processing of Audio Signals

    E-print Network

    Mosegaard, Klaus

    Alpha-Stable Distributions in Signal Processing of Audio Signals Preben Kidmose, Department of Mathematical Modelling, Section for Digital Signal Processing, Technical University of Denmark, Building 321 the applicability of stable distributions in audio processing, a classical problem from statistical signal

  11. Compact and stable dual-fiber-optic refracting collimator

    Microsoft Academic Search

    David M. Stubbs; Eric Smith; Lawrence Dries; Todd Kvamme; Stephanie Barrett

    2003-01-01

    The compact and stable dual fiber optic refractive collimator is a device that takes laser light from two fiber optic cables, generating two beams of collimated light at increased diameters. This device is designed to be stable over a specific soak temperature range and maintain alignment through adverse vibration. Single or multiple beam configurations are possible with this design and

  12. Stable matchings in three-sided systems with cyclic preferences

    Microsoft Academic Search

    Endre Boros; Vladimir Gurvich; Steven Jaslar; Daniel Krasner

    2004-01-01

    We consider generalizations of the Gale–Shapley (Amer. Math. Monthly 69 (1962) 9) Stable Marriage Problem to three-sided families. Alkan (Math. Social Sci. 16 (1988) 207) gave an example which shows that in this case stable matchings do not always exist. Here we provide a simpler example demonstrating this fact. Danilov (NATO Advanced Research Workshop on Mathematical Theory of Allocation of

  13. Stable structures with high topological charge in nonlinear photonic quasicrystals

    E-print Network

    Law, K J H; Kevrekidis, P G; Bishop, A R

    2010-01-01

    Stable vortices with topological charge of 3 and 4 are examined numerically and analytically in photonic quasicrystals created by interference of 5 as well as 8 beams, in the cases of cubic as well as saturable nonlinearities. These structures are experimentally realizable, including a prototypical example of a stable charge 4 vortex. Direct numerical simulations corroborate the analytical and numerical linear stability analysis predictions.

  14. Absolute continuity of stable foliations for systems on Banach spaces

    NASA Astrophysics Data System (ADS)

    Lian, Zeng; Young, Lai-Sang; Zeng, Chongchun

    We prove the absolute continuity of stable foliations for C maps of Banach spaces satisfying a globally defined infinitesimal invariant cones condition. Proofs of regularity for center and stable manifolds needed for the main theorem are included. Our results are applicable to dynamical systems generated by ordinary, partial, or functional differential equations, including non-autonomous differential equations that are periodic in time.

  15. STABLE BANACH SPACES AND BANACH SPACE STRUCTURES, II

    E-print Network

    Iovino, José - Iovino, José

    by finiteness is mirrored by compactness. Section 7 is devoted to superstability. To characterize superstability is superstable but not - stable with respect to the metric d on the space types, and an example of a structure which is stable but not superstable with respect to the same metric. Both structures consist of Hilbert

  16. Heavy Network Traffic Modeling and Simulation using Stable FARIMA Processes

    Microsoft Academic Search

    F. C. Harmantzis; D. Hatzinakos

    Fractionally autoregressive integrated moving average (FARIMA) processes have been proposed for network traffic modeling. In this paper we focus on the gener- alization of those processes, considering heavy-tailed (Stable) innovations. The resulted linear Stable FARIMA model captures the short and long range dependences as well as the heavy-tailed behavior of the network traffic. The contribution is an integrated procedure of

  17. Stable isotopes as one of nature's ecological recorders

    E-print Network

    Ehleringer, Jim

    Stable isotopes as one of nature's ecological recorders Jason B. West1 , Gabriel J. Bowen2 , Thure of the natural variation in stable isotopes of components of ecological systems have provided new insights of spatial scales. Isotope abundances of the molecules in biological materials and geochemical profiles

  18. Stable Manifold Embeddings with Operators Satisfying the Restricted Isometry Property

    E-print Network

    Rozell, Christopher J.

    that these structures have been shown to support stable, distance-preserving embeddings via linear mappings into a lower-dimensional) to obtain a stable embedding of a manifold. Index Terms--Manifold Embedding, Dimensionality Re- duction on the observation that many high- dimensional signals in fact have an intrinsic low- dimensional structure. Models

  19. Mass exchange in the stable boundary layer by coherent structures

    E-print Network

    Leclerc, Monique Y.

    Mass exchange in the stable boundary layer by coherent structures D.I. Cooper a,*, M.Y. Leclerc b December 2004 Abstract Observations of multi-dimensional water vapor structures in the first 75 m of the stable boundary layer (SBL) were made using a high resolution scanning Raman lidar in October 2000 during

  20. Treatment of stable vitiligo with autologous epidermal grafting and PUVA

    Microsoft Academic Search

    Seung Kyung Hann; Sungbin Im; Ha Wook Bong; Yoon-Kee Park

    1995-01-01

    Background: Previous reports have shown the benefits of epidermal grafting for vitiligo.Objective: Our purpose was to evaluate the effectiveness and complications of epidermal grafting in combination with PUVA on stable vitiligo refractory to conventional treatments.Methods: In 100 patients with stable refractory vitiligo we performed epidermal grafting with suction blisters followed by PUVA treatment. The grafted sites were examined for repigmentation

  1. Stable, concentrated solutions of polyaniline using amines as gel inhibitors

    Microsoft Academic Search

    Hsing-Lin Wang; Benjamin R. Mattes

    2002-01-01

    Stable, concentrated solutions of high-molecular weight polyaniline using amines as gel inhibitors. Certain amine compounds (gel inhibitors) are used to form highly concentrated, stable solutions of the emeraldine base form of polyaniline in numerous organic solvents from which coatings, films and fibers are readily prepared without problems associated with rapid gelation which occurs when concentrated solutions are attempted without the

  2. Potential Theory of Special Subordinators and Subordinate Killed Stable Processes

    E-print Network

    Vondraèek, Zoran

    Potential Theory of Special Subordinators and Subordinate Killed Stable Processes Renming Song their potential theory. Then we study the potential theory of processes obtained by subordinating a killed-to-one correspondence between the nonnegative harmonic functions of the killed symmetric stable process and the non

  3. Stable Isotopes and Mineral Resource Investigations in the United States

    NSDL National Science Digital Library

    This USGS handout is a page providing a good, brief summary of stable isotope techniques and applications in the geosciences. A map indicating the locations of current USGS stable isotopic studies accompanies the text. A discussion of mineral weathering effects and case studies from ore deposits in Maine and North Carolina complement the general overview.

  4. Stable shape of bodies disintegrating due to aerodynamic heating

    Microsoft Academic Search

    V. G. Voronkin; V. V. Lunev; A. N. Nikulin

    1978-01-01

    In the present paper, solutions to an equation describing the stable shape of ablating bodies are obtained using a simplified formulation of the problem (assuming a local law for the pressure and for the heat flux distribution). It is shown that this problem does not possess a solution in the class of smooth functions and that the stable contour of

  5. A VIEW OF THE STABLES LOOKING TO THE SOUTH, TOWARD ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    A VIEW OF THE STABLES LOOKING TO THE SOUTH, TOWARD THE HUACHUCA MOUNTAINS, CIRCA 1910. HORSES ARE TIED TO THE EXTERIOR OF ONE OF THE PADDOCK CORRALS (FORT HUACHUCA HISTORICAL MUSEUM, PHOTOGRAPH 1918.00.00.126, PHOTOGRAPHER UNIDENTIFIED, CREATED BY AND PROPERTY OF THE UNITED STATES ARMY) - Fort Huachuca, Cavalry Stables, Clarkson Road, Sierra Vista, Cochise County, AZ

  6. Peer Reviewed Temporal Variation in Stable Carbon and Nitrogen

    E-print Network

    Gillingham, Michael

    to distinguish among seasonal assimilated diets of grizzly bears (Ursus arctos) by comparing the isotopic values, nitrogen, stable isotope, technique, Ursus arctos. Traditional methods of examining the diet of animals, Robbins et al. 2004). Specifically in bears (Ursus spp.), the stable isotopes of carbon (13 C/12 C

  7. On fractional tempered stable processes and their governing differential equations

    NASA Astrophysics Data System (ADS)

    Beghin, Luisa

    2015-07-01

    We derive the governing equation of the Tempered Stable Subordinator (hereafter TSS), which generalizes the space-fractional differential equation satisfied by the law of the ?-stable subordinator itself. This equation is expressed in terms of the shifted fractional derivative of order ? ? (0 , 1) coinciding with the stability parameter. We then generalize this equation by introducing a time-fractional derivative of order ? ? (0 , 1) (resp. 1 / ? > 1) and we prove that it is satisfied by the law of a TSS time-changed by the inverse of a ?-stable subordinator (resp. by the stable subordinator itself). The corresponding processes can therefore be called "fractional TS processes". Finally we provide fractional extensions of the relativistic stable processes, which we define as a Brownian motion with a random time argument represented by independent fractional TS processes of order ? (resp. 1 / ?).

  8. Compact, Highly Stable Ion Atomic Clock

    NASA Technical Reports Server (NTRS)

    Prestage, John

    2008-01-01

    A mercury-ion clock now at the breadboard stage of development (see figure) has a stability comparable to that of a hydrogen-maser clock: In tests, the clock exhibited an Allan deviation of between 2 x 10(exp -13) and 3 x 10(exp -13) at a measurement time of 1 second, averaging to about 10(exp -15) at 1 day. However, the clock occupies a volume of only about 2 liters . about a hundredth of the volume of a hydrogen-maser clock. The ion-handling parts of the apparatus are housed in a sealed vacuum tube, wherein only a getter pump is used to maintain the vacuum. Hence, this apparatus is a prototype of a generation of small, potentially portable high-precision clocks for diverse ground- and space-based navigation and radio science applications. Furthermore, this new ion-clock technology is about 100 times more stable and precise than the rubidium atomic clocks currently in use in the NAV STAR GPS Earth-orbiting satellites. In this clock, mercury ions are shuttled between a quadrupole and a 16-pole linear radio-frequency trap. In the quadrupole trap, the ions are tightly confined and optical state selection from a Hg-202 radio-frequency-discharge ultraviolet lamp is carried out. In the 16-pole trap, the ions are more loosely confined and atomic transitions resonant at frequency of about 40.507 GHz are interrogated by use of a microwave beam at that frequency. The trapping of ions effectively eliminates the frequency pulling caused by wall collisions inherent to gas-cell clocks. The shuttling of the ions between the two traps enables separation of the state-selection process from the clock microwave- resonance process, so that each of these processes can be optimized independently of the other. The basic ion-shuttling, two-trap scheme as described thus far is not new: it has been the basis of designs of prior larger clocks. The novelty of the present development lies in major redesigns of its physics package (the ion traps and the vacuum and optical subsystems) to effect the desired reduction of size to a volume of no more than a couple of liters. The redesign effort has included selection of materials for the vacuum tube, ion trap, and ultraviolet windows that withstand bakeout at a temperature of approx.450 C in preparation for sealing the tube to contain the vacuum. This part of the redesign effort follows the approach taken in the development of such other vacuum-tube electronic components as flight traveling- wave-tube amplifiers having operational and shelf lives as long as 15 years. The redesign effort has also included a thorough study of residual-gas-induced shifts of the ion-clock frequency and a study of alternative gases as candidates for use as a buffer gas within the sealed tube. It has been found that neon is more suitable than is helium, which has been traditionally used for this purpose, in that the pressure-induced frequency pulling by neon is between a third and a half of that of helium. In addition, because neon diffuses through solids much more slowly than does helium, the loss of neon by diffusion over the operational lifetime is expected to be negligible.

  9. Stable Chlorine Isotopes in Ocean Crust Processes

    NASA Astrophysics Data System (ADS)

    Bach, W.; Layne, G.; Kent, A.

    2003-12-01

    The study of natural variations of Cl isotopic composition in ocean crustal rocks has large potential to further our understanding of geochemical cycling of volatiles and elements soluble in saline aqueous solutions. Studies of oceanic basalt suites to date confirm that Cl abundances are highly sensitive to the addition of saline components - either from addition of subduction-related volatile fluxes in back-arc basins and volcanic arcs or via interaction between magmas and Cl-rich seawater-derived components during melting, magma storage and transport. Recent data suggest that ? 37Cl is much more variable in the marine environment than originally thought, with strongly negative ? 37Cl values (down to -7.5 ‰ ) in marine pore waters and positive values (up to +7 ‰ ) in hydrothermal fluids from oceanic spreading centers. Moreover, mantle-derived magmatic rocks reveal large variations in ? 37Cl (-3 to +11 ‰ ), reflecting mantle heterogeneity as well as assimilation of exogenic Cl by crystallizing magmas. The large isotopic variation in low-Cl basalts has been explained by isotopic heterogeneities of the mantle, with very light ? 37Cl values in rocks from the southwest Chile Ridge that have island arc geochemical affinities and heavy ? 37Cl values in Reykjanes Ridge samples (Stewart, 2000, PhD Thesis, Duke University). The inference is that a slab-flux carries a negative ? 37Cl signature while recycled ocean crust in mantle plumes carries a strongly positive ? 37Cl signature, although this is not well constrained at present. Preferential release of isotopically light Cl from the dewatering sediments is suggested by pore water data from the Barbados and Nankai accretionary prisms with ? 37Cl values down to -7.5 ‰ (Ransom et al. 1995, Geology, 23, 715). Volcanic fumaroles also appear to have negative ? 37Cl values. If this is the case then residual Cl in the subducting slab should become isotopically heavier as 35Cl is preferentially released in the shallow subduction zone. The depleted MORB mantle is believed to have a ? 37Cl between 4 and 7 ‰ , similar to C1-chondrite (Magenheim et al., 1995, EPSL, 131, 427). MORB with high Cl and Cl/K tend to have ? 37Cl close to 0 ‰ , which has been explained by contamination of basaltic magmas with seawater-derived Cl. However, the most evolved ferrobasalts and andesites from oceanic spreading ridges have negative ? 37Cl values, down to -1.7 ‰ (Magenheim, unpublished data). Together with data for oceanic gabbros, the ? 37Cl-[Cl] data for these highly evolved rocks form a trend that could be explained by an AFC-like process, although the fact that the trend extends to negative ? 37Cl values cannot be reconciled with batch mixing of magma and salt or brine. Rather, it indicates that 35Cl is preferentially incorporated into the magma and may be related to diffusive exchange between Cl in brine pools above the melt lens of an axial magma system. A more comprehensive global dataset as well as spot analyses of Cl isotope ratios by IMP-SIMS (e.g., of melt inclusions) and the combination of ? 37Cl with other stable isotope systems (B, Li, O, H) are required before these tentative models for global chlorine cycling and crustal assimilation at spreading ridges can be rigorously evaluated.

  10. Use of stable isotopes in mineral nutrition research

    SciTech Connect

    Turnlund, J.R.

    1989-01-01

    Stable isotopes are valuable tools for research on mineral bioavailability and metabolism. They can be used as tracers with no exposure to radiation and they do not decay over time. Attempts to use stable isotopes of minerals as metabolic tracers were first described only 25 years ago. There were relatively few reports of their use over the next 15 years, but interest in stable isotopes has expanded markedly in the last 10 years. The advantages of stable isotope tracers are so great that scientists have been willing to accept the laborious and costly nature of mineral isotope analysis, and substantial progress has been made in the field. New applications for stable isotopes and new analytical methods have been introduced recently. However, limitations to the approach and methodological problems remain to be resolved. This review describes early work in the field and discusses the advantages and disadvantages of stable isotope tracers and of the various methods of analysis. Information discovered with stable isotopes is reviewed, and probable future applications are discussed.69 references.

  11. Stable superhydrophobic surfaces over a wide pH range

    NASA Astrophysics Data System (ADS)

    Guo, Li; Yuan, Wenfang; Li, Junping; Zhang, Zhijie; Xie, Zemin

    2008-01-01

    A stable superhydrophobic surface was fabricated by solidifying poly(epoxy-terminated polydimethylsiloxane- co-bisphenol A) [P(ETPDMS- co-BPA)] copolymer on a rough substrate. The low surface energy of the copolymer and the geometric structure at micrometer scale of the surface contribute to the superhydrophobic property. The as-prepared surface shows stable superhydrophobicity over a wide pH range (1-14) and the wettability is excellent stable to heating, water, corrosive solution and organic solvent treatments. The procedure is simple and time-saving as well as utilizing non-fluorine-containing compounds.

  12. Versatile Synthesis of Stable, Functional Polypeptides via Reaction with Epoxides.

    PubMed

    Gharakhanian, Eric G; Deming, Timothy J

    2015-06-01

    Methodology was developed for efficient alkylation of methionine residues using epoxides as a general strategy to introduce a wide range of functional groups onto polypeptides. Use of a spacer between epoxide and functional groups further allowed addition of sterically demanding functionalities. Contrary to other methods to alkylate methionine residues, epoxide alkylations allow the reactions to be conducted in wet protic media and give sulfonium products that are stable against dealkylation. These functionalizations are notable since they are chemoselective, utilize stable and readily available epoxides, and allow facile incorporation of an unprecedented range of functional groups onto simple polypeptides using stable linkages. PMID:25974116

  13. Calabi–Yau varieties with semi-stable fibre structures

    Microsoft Academic Search

    Yi Zhang; Kang Zuo

    2008-01-01

    Motivated by the Strominger–Yau–Zaslow conjecture, we study Calabi–Yau varieties with semi-stable fibre structures. We use\\u000a Hodge theory to study the higher direct images of wedge products of relative cotangent sheaves of certain semi-stable families\\u000a over higher dimensional quasi-projective bases, and obtain some results on positivity. We then apply these results to study\\u000a non-isotrivial Calabi–Yau varieties fibred by semi-stable Abelian varieties

  14. Environmental and biomedical applications of natural metal stable isotope variations

    USGS Publications Warehouse

    Bullen, T.D.; Walczyk, T.

    2009-01-01

    etal stable isotopes are now being used to trace metal contaminants in the environment and as indicators of human systemic function where metals play a role. Stable isotope abundance variations provide information about metal sources and the processes affecting metals in complex natural systems, complementing information gained from surrogate tracers, such as metal abundance ratios or biochemical markers of metal metabolism. The science is still in its infancy, but the results of initial studies confirm that metal stable isotopes can provide a powerful tool for forensic and biomedical investigations.

  15. A new intermediate for the production of flexible stable polymers

    NASA Technical Reports Server (NTRS)

    Webster, J. A.

    1973-01-01

    Method of incorporating ether linkages into perfluoroalkylene segment of a dianydride intermediate yields intermediate that may be used in synthesis of flexible, stable polyimides for use as high-temperature, solvent-resistant sealants.

  16. STABLE ISOTOPES IN ECOLOGICAL STUDIES: NEW DEVELOPMENTS IN MIXING MODELS

    EPA Science Inventory

    Stable isotopes are increasingly being used as tracers in ecological studies. One application uses isotopic ratios to quantify the proportional contributions of multiple sources to a mixture. Examples include food sources for animals, water sources for plants, pollution sources...

  17. STABLE ISOTOPIC RESPONSE TO THE LATE EOCENE EXTRATERRESTRIAL IMPACT EVENTS

    E-print Network

    STABLE ISOTOPIC RESPONSE TO THE LATE EOCENE EXTRATERRESTRIAL IMPACT EVENTS by AIMEE E PUSZ A thesis to the Late Eocene Extraterrestrial Impact Events by AIMEE ELIZABETH PUSZ Thesis Director: Dr. Kenneth G

  18. Original article Are stable flies (Diptera: Stomoxyinae) vectors of

    E-print Network

    Paris-Sud XI, Université de

    of stable flies were encountered: Sto- moxys nigra nigra (approximately 60% of the sample), S taeniata ou sous-espèces de stomoxes ont été recensées : Stomoxys nigra nigra (approximativement 60 % de l

  19. Stable electrical contacts to thin films at low temperatures

    NASA Astrophysics Data System (ADS)

    Guillon, F.; Julien, C.; Cheeke, J. D. N.

    1987-08-01

    We describe some techniques for making reliable and stable electrical contact to thin films using a gold wire bonding machine. Applications of these techniques to specific low-temperature experiments are given.

  20. Overwintering of the stable fly (Diptera: Muscidae) in southeastern Nebraska.

    PubMed

    Berkebile, D R; Thomas, G D; Campbell, J B

    1994-12-01

    Adult stable flies, Stomoxys calcitrans (L.), were monitored during three winters at two, four, and 13 locations with Alsynite fiberglass traps and by examination of the interiors of buildings. No stable flies were found inside buildings during the winter. Adult stable flies were consistently caught on Alsynite traps at one location during two winters and at two other locations during one winter. Distribution and physiological age of these flies indicate that they emerged from pupae that had developed at or near the location where they were captured. Potential breeding sites were examined. A few third instars were found in silage in midwinter, but silage should not be considered a major source for overwintering stable flies. PMID:7836614

  1. Comparative efficiency of six stable fly (Diptera: Muscidae) traps.

    PubMed

    Taylor, David B; Berkebile, Dennis

    2006-08-01

    Five adhesive traps and the Nzi cloth-target trap were compared to determine their trapping efficiency and biases for stable flies, Stomoxys calcitrans (L.) (Diptera: Muscidae). Two configurations of the BiteFree prototype trap, constructed of polyethylene terephthalate, were most efficient for trapping stable flies, whereas the EZ trap was least efficient. The two Alsynite traps, Broce and Olson, were intermediate to the BiteFree prototype and EZ traps. All adhesive traps collected a ratio of approximately two males for each female. Approximately 50% of the flies collected on the adhesive traps, both male and female, were blood fed, and 20% were vitellogenic. The Nzi trap collected an older component of the stable fly population, 81% blood fed and 62% vitellogenic, but it was much less efficient than the adhesive traps. The effectiveness of the BiteFree prototype trap indicates that materials other than Alsynite are attractive to stable flies. PMID:16937700

  2. Understanding stable levitation of superconductors from intermediate electromagnetics

    E-print Network

    Majós, Antonio Badía

    Understanding stable levitation of superconductors from intermediate electromagnetics A. Bad for electromagnetic energy related quantities. Comprehensible illustrations, based on the calculated lines of magnetic at students who have followed an intermediate course on Electromagnetics and have some background in Classical

  3. Dark Atoms of Dark Matter and their Stable Charged Constituents

    E-print Network

    Khlopov, Maxim Yu

    2011-01-01

    Direct searches for dark matter lead to serious problems for simple models with stable neutral Weakly Interacting Massive Particles (WIMPs) as candidates for dark matter. A possibility is discussed that new stable quarks and charged leptons exist and are hidden from detection, being bound in neutral dark atoms of composite dark matter. Stable -2 charged particles $O^{--}$ are bound with primordial helium in O-helium (OHe) atoms, being specific nuclear interacting form of composite dark matter. The positive results of DAMA experiments can be explained as annual modulation of radiative capture of O-helium by nuclei. In the framework of this approach test of DAMA results in detectors with other chemical content becomes a nontrivial task, while the experimental search of stable charged particles at LHC or in cosmic rays acquires a meaning of direct test for composite dark matter scenario.

  4. 9 CFR 108.10 - Outer premises and stables.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ...108.10 Section 108.10 Animals and Animal Products ANIMAL AND PLANT HEALTH INSPECTION SERVICE, DEPARTMENT...premises. (b) Stables or other premises for animals used in the production or testing of biological products at licensed...

  5. Stable isotope views on ecosystem function: challenging or challenged?

    PubMed Central

    Resco, Víctor; Querejeta, José I.; Ogle, Kiona; Voltas, Jordi; Sebastià, Maria-Teresa; Serrano-Ortiz, Penélope; Linares, Juan C.; Moreno-Gutiérrez, Cristina; Herrero, Asier; Carreira, José A.; Torres-Cañabate, Patricia; Valladares, Fernando

    2010-01-01

    Stable isotopes and their potential for detecting various and complex ecosystem processes are attracting an increasing number of scientists. Progress is challenging, particularly under global change scenarios, but some established views have been challenged. The IX meeting of the Spanish Association of Terrestrial Ecology (AAET, Úbeda, 18–22 October 2009) hosted a symposium on the ecology of stable isotopes where the linear mixing model approach of partitioning sinks and sources of carbon and water fluxes within an ecosystem was challenged, and new applications of stable isotopes for the study of plant interactions were evaluated. Discussion was also centred on the need for networks that monitor ecological processes using stable isotopes and key ideas for fostering future research with isotopes. PMID:20015858

  6. 15 CFR 971.605 - Stable Reference Areas. [Reserved

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ...OCEANIC AND ATMOSPHERIC ADMINISTRATION, DEPARTMENT OF COMMERCE GENERAL REGULATIONS OF THE ENVIRONMENTAL DATA SERVICE DEEP SEABED MINING REGULATIONS FOR COMMERCIAL RECOVERY PERMITS Environmental Effects § 971.605 Stable Reference Areas....

  7. 15 CFR 971.605 - Stable Reference Areas. [Reserved

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ...OCEANIC AND ATMOSPHERIC ADMINISTRATION, DEPARTMENT OF COMMERCE GENERAL REGULATIONS OF THE ENVIRONMENTAL DATA SERVICE DEEP SEABED MINING REGULATIONS FOR COMMERCIAL RECOVERY PERMITS Environmental Effects § 971.605 Stable Reference Areas....

  8. Speed of light as measured by two terrestrial stable clocks

    NASA Technical Reports Server (NTRS)

    Hsu, J. P.; Sherry, T. N.; Chiu, C. B.

    1977-01-01

    Despite the recent criticism within the special theory of relativity, there exists an arrangement of stable clocks rotating with the earth which predicts diurnal variations of the one-way speed of light, as suggested previously.

  9. 9 CFR 108.10 - Outer premises and stables.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ...PLANT HEALTH INSPECTION SERVICE, DEPARTMENT OF AGRICULTURE VIRUSES, SERUMS, TOXINS, AND ANALOGOUS PRODUCTS; ORGANISMS AND VECTORS FACILITY REQUIREMENTS FOR LICENSED ESTABLISHMENTS § 108.10 Outer premises and stables. (a) The outer...

  10. 9 CFR 108.10 - Outer premises and stables.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ...PLANT HEALTH INSPECTION SERVICE, DEPARTMENT OF AGRICULTURE VIRUSES, SERUMS, TOXINS, AND ANALOGOUS PRODUCTS; ORGANISMS AND VECTORS FACILITY REQUIREMENTS FOR LICENSED ESTABLISHMENTS § 108.10 Outer premises and stables. (a) The outer...

  11. BIODEGRADATION OF FLUORANTHENE AS MONITORED USING STABLE CARBON ISOTOPES

    EPA Science Inventory

    The measurement of stable isotope ratios of carbon (d13C values) was investigated as a viable technique to monitor the intrinsic bioremediation of polycyclic aromatic hydrocarbons (PAHs). Biometer-flask experiments were conducted in which the bacterium, Sphingomonas paucimobilis,...

  12. Dynamically-Stable Motion Planning for Humanoid Robots

    Microsoft Academic Search

    James J. Kuffner; Satoshi Kagami; Koichi Nishiwaki; Masayuki Inaba; Hirochika Inoue

    2002-01-01

    We present an approach to path planning for humanoid robots that computes dynamically-stable, collision-free trajectories from full-body posture goals. Given a geometric model of the environment and a statically-stable desired posture, we search the configuration space of the robot for a collision-free path that simultaneously satisfies dynamic balance constraints. We adapt existing randomized path planning techniques by imposing balance constraints

  13. Meta-Stable Brane Configurations by Quartic Superpotential for Bifundamentals

    NASA Astrophysics Data System (ADS)

    Ahn, Changhyun

    The type IIA nonsupersymmetric meta-stable brane configuration consisting of three NS5-branes, D4-branes and anti-D4-branes where the electric gauge theory superpotential has a quartic term for the bifundamentals besides a mass term is constructed. By adding the orientifold 4-plane and 6-plane to this brane configuration, we also describe the intersecting brane configurations of type IIA string theory corresponding to the meta-stable nonsupersymmetric vacua of corresponding gauge theories.

  14. Stable isotopes in precipitation in the Asian monsoon region

    Microsoft Academic Search

    M. Vuille; M. Werner; R. S. Bradley; F. Keimig

    2005-01-01

    The influence of the Asian monsoon on the delta18O composition of precipitation is investigated on the basis of the ECHAM-4 Atmospheric General Circulation Model (AGCM), fitted with stable isotopic tracers. The model is forced with prescribed sea surface temperatures (SST) over the last few decades of the 20th century. The simulated climate and climate-stable isotope relationships are validated with observational

  15. Convergence to a Stable Distribution Via Order Statistics

    Microsoft Academic Search

    Raoul LePage; Michael Woodroofe; Joel Zinn

    1981-01-01

    Let $X_1, X_2, \\\\cdots$ be i.i.d. random variables whose common distribution function $F$ is in the domain of attraction of a nonnormal stable distribution. A simple, probabilistic proof of the convergence of the normalized partial sums to the stable distribution is given. The proof makes use of an elementary property of order statistics and clarifies the manner in which the

  16. Dantzig-Wolfe decomposition for linearly constrained stable set problem

    E-print Network

    Boyer, Edmond

    Dantzig-Wolfe decomposition for linearly constrained stable set problem Virginie Gabrel Résumé Nous considérons l'application d'un schéma de décomposition de Dantzig-Wolfe sur un programme linéaire en variables départ. Mots-clefs : Decomposition de Dantzig-Wolfe, polytope du stable, graphe parfait Abstract We

  17. A Stable Quasicrystal in Al-Cu-Fe System

    Microsoft Academic Search

    An-Pang Tsai; Akihisa Inoue; Tsuyoshi Masumoto

    1987-01-01

    A thermodynamically stable quasicrystalline single phase with an icosahedral structure was found to be formed at an atomic composition of Al65Cu20Fe15 in a fully annealed state as well as in a conventionally solidified state. The stable quasicrystal consisted of large grains with an average size of 0.2 mm after annealing for 48 h at 1118 K (0.98 Tm).

  18. Pushing the limits with high intensity stable ion beams

    NASA Astrophysics Data System (ADS)

    Azaiez, F.; DeAngelis, G.; Herzberg, R.-D.; Hofmann, S.; Julin, R.; Lewitowicz, M.; Moscatello, M. H.; Porcellato, A. M.; Ratzinger, U.

    2006-08-01

    This contribution is a brief report on the document that has been elaborated and prepared by the ECoS (European Collaboration on Stable ion beams) working group, in order to describe the research perspectives with high intensity stable ion beams, to help categorize existing facilities regarding their up-grade to higher intensities and to identify the opportunities for a dedicated new facility in EUROPE.

  19. Pushing the limits with high intensity stable ion beams

    SciTech Connect

    Azaiez, F. [IPN-Orsay, Orsay (France); DeAngelis, G.; Porcellato, A. M. [LNL, Legnaro (Italy); Herzberg, R.-D. [University of Liverpool, Liverpool (United Kingdom); Hofmann, S. [GSI, Darmshdat (Germany); Julin, R. [University of Jyvaslyla (Finland); Lewitowicz, M.; Moscatello, M. H. [GANIL, Caen (France); Ratzinger, U. [IAP, IAP, Frankfurt (Germany)

    2006-08-14

    This contribution is a brief report on the document that has been elaborated and prepared by the ECoS (European Collaboration on Stable ion beams) working group, in order to describe the research perspectives with high intensity stable ion beams, to help categorize existing facilities regarding their up-grade to higher intensities and to identify the opportunities for a dedicated new facility in EUROPE.

  20. 7. OVERALL VIEW OF ROOM 110 (STABLES), LOOKING EAST. THE ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    7. OVERALL VIEW OF ROOM 110 (STABLES), LOOKING EAST. THE LONG, LOW SPACE IS DIVIDED INTO AISLES BY EXPOSED POSTS AND BEAMS; POSTS ARE PAINTED. CEILING TREATMENT CHANGES FROM GYPSUM BOARD TO WOOD PLANKS IN THE CENTER AISLE. THE CONCRETE SLAB FLOOR IS SLOPED FROM CENTER FOR DRAINAGE PURPOSES. SMALL, HIGH WINDOWS LINE THE NORTHEAST AND SOUTHWEST WALLS. - Presidio of San Francisco, Cavalry Stables, Cowles Street, between Lincoln Boulevard & McDowell Street, San Francisco, San Francisco County, CA

  1. Stable inverse control for nonminimum-phase nonlinear processes

    Microsoft Academic Search

    Wei Wu

    1999-01-01

    Since most of the chemical processes happen to be nonlinear, nonlinear controllers with feedback linearization have been recently designed which can directly cancel the nonlinearities and establish a linear input\\/output map. However, this I\\/O linearization algorithm requires the control with stable inversion and state feedback. In the present study, a stable inversion technique for nonminimum-phase systems is developed under appropriate

  2. Gelled mechanically stable high energy fuel composition containing metal platelets

    SciTech Connect

    Bost, J.J.; Cabeal, J.A.; Rosenberg, S.D.

    1980-02-05

    A gelled mechanically stable high energy fuel composition is disclosed comprising a hydrazine selected from the group consisting of hydrazine, unsymmetrical dimethyl hydrazine and mixtures thereof and an amount of metal platelets effective to produce a mechanically stable gel. Said platelets have a diameter of less than about 44 microns and an average diameter of about 1 micron, and said metal platelets are composed of a metal selected from the group consisting of aluminum, beryllium and aluminumberyllium alloy.

  3. The use of stable isotopes to study ecosystem gas exchange

    Microsoft Academic Search

    D. Yakir; L. da S. L. Sternberg

    2000-01-01

    Stable isotopes are a powerful research tool in environmental sciences and their use in ecosystem research is increasing.\\u000a In this review we introduce and discuss the relevant details underlying the use of carbon and oxygen isotopic compositions\\u000a in ecosystem gas exchange research. The current use and potential developments of stable isotope measurements together with\\u000a concentration and flux measurements of CO2

  4. Entropy stable schemes for initial-boundary-value conservation laws

    NASA Astrophysics Data System (ADS)

    Svärd, Magnus; Mishra, Siddhartha

    2012-12-01

    We consider initial-boundary-value problems for systems of conservation laws and design entropy stable finite difference schemes to approximate them. The schemes are shown to be entropy stable for a large class of systems that are equipped with a symmetric splitting, derived from the entropy formulation. Numerical examples for the Euler equations of gas dynamics are presented to illustrate the robust performance of the proposed method.

  5. Equilibrium contact angle or the most-stable contact angle?

    PubMed

    Montes Ruiz-Cabello, F J; Rodríguez-Valverde, M A; Cabrerizo-Vílchez, M A

    2014-04-01

    It is well-established that the equilibrium contact angle in a thermodynamic framework is an "unattainable" contact angle. Instead, the most-stable contact angle obtained from mechanical stimuli of the system is indeed experimentally accessible. Monitoring the susceptibility of a sessile drop to a mechanical stimulus enables to identify the most stable drop configuration within the practical range of contact angle hysteresis. Two different stimuli may be used with sessile drops: mechanical vibration and tilting. The most stable drop against vibration should reveal the changeless contact angle but against the gravity force, it should reveal the highest resistance to slide down. After the corresponding mechanical stimulus, once the excited drop configuration is examined, the focus will be on the contact angle of the initial drop configuration. This methodology needs to map significantly the static drop configurations with different stable contact angles. The most-stable contact angle, together with the advancing and receding contact angles, completes the description of physically realizable configurations of a solid-liquid system. Since the most-stable contact angle is energetically significant, it may be used in the Wenzel, Cassie or Cassie-Baxter equations accordingly or for the surface energy evaluation. PMID:24140073

  6. Medieval horse stable; the results of multi proxy interdisciplinary research.

    PubMed

    Dejmal, Miroslav; Lisá, Lenka; Fišáková Nývltová, Miriam; Bajer, Aleš; Petr, Libor; Ko?ár, Petr; Ko?árová, Romana; Nejman, Ladislav; Rybní?ek, Michal; S?vová, Zdenka; Culp, Randy; Vavr?ík, Hanuš

    2014-01-01

    A multi proxy approach was applied in the reconstruction of the architecture of Medieval horse stable architecture, the maintenance practices associated with that structure as well as horse alimentation at the beginning of 13th century in Central Europe. Finally, an interpretation of the local vegetation structure along Morava River, Czech Republic is presented. The investigated stable experienced two construction phases. The infill was well preserved and its composition reflects maintenance practices. The uppermost part of the infill was composed of fresh stabling, which accumulated within a few months at the end of summer. Horses from different backgrounds were kept in the stable and this is reflected in the results of isotope analyses. Horses were fed meadow grasses as well as woody vegetation, millet, oat, and less commonly hemp, wheat and rye. Three possible explanations of stable usage are suggested. The stable was probably used on a temporary basis for horses of workers employed at the castle, courier horses and horses used in battle. PMID:24670874

  7. Study on stable and meta-stable carbides in a high speed steel for rollers during tempering processes

    NASA Astrophysics Data System (ADS)

    Guo, Jing; Qu, Hong-wei; Liu, Li-gang; Sun, Yan-liang; Zhang, Yue; Yang, Qing-xiang

    2013-02-01

    A high speed steel (HSS) was studied for rollers in this work. The steel was quenched at 1150°C and tempered at 520°C. The phase structures of the steel were determined by X-ray diffraction (XRD), and the hardness of specimens was measured. The volume fraction of carbides was counted by Image-Pro Plus software. The typical microstructures were observed by field emission scanning electron microscope (FESEM). Stable and meta-stable carbides were deduced by removing the existing phases one by one in the Fe-C equilibrium calculation. It is found that the precipitated carbides are bulk-like MC, long stripe-like M2C, fishbone-like M6C, and daisy-like M7C3 during the tempering process. The stable carbides are MC and M6C, but the meta-stable ones are M2C, M7C3, and M3C.

  8. Compound specific stable isotope analysis vs. bulk stable isotope analysis of agricultural food products

    NASA Astrophysics Data System (ADS)

    Psomiadis, David; Horváth, Balázs; Nehlich, Olaf; Bodiselitsch, Bernd

    2015-04-01

    The bulk analysis of stable isotopes (carbon, nitrogen, sulphur, oxygen and hydrogen) from food staples is a common tool for inferring origin and/or fraud of food products. Many studies have shown that bulk isotope analyses of agricultural products are able to separate large geographical areas of food origin. However, in micro-localities (regions, districts, and small ranges) these general applications fail in precision and discriminative power. The application of compound specific analysis of specific components of food products helps to increase the precision of established models. Compound groups like fatty acids (FAMEs), vitamins or amino acids can help to add further detailed information on physiological pathways and local conditions (micro-climate, soil, water availability) and therefore might add further information for the separation of micro-localities. In this study we are aiming to demonstrate the power and surplus of information of compound specific isotope analysis in comparison to bulk analysis of agricultural products (e.g. olive oil, cereal crops or similar products) and discuss the advantages and disadvantages of such (labor intense) analysis methods. Here we want to identify tools for further detailed analysis of specific compounds with high powers of region separation for better prediction models.

  9. Multi-stable perception balances stability and sensitivity.

    PubMed

    Pastukhov, Alexander; García-Rodríguez, Pedro E; Haenicke, Joachim; Guillamon, Antoni; Deco, Gustavo; Braun, Jochen

    2013-01-01

    We report that multi-stable perception operates in a consistent, dynamical regime, balancing the conflicting goals of stability and sensitivity. When a multi-stable visual display is viewed continuously, its phenomenal appearance reverses spontaneously at irregular intervals. We characterized the perceptual dynamics of individual observers in terms of four statistical measures: the distribution of dominance times (mean and variance) and the novel, subtle dependence on prior history (correlation and time-constant). The dynamics of multi-stable perception is known to reflect several stabilizing and destabilizing factors. Phenomenologically, its main aspects are captured by a simplistic computational model with competition, adaptation, and noise. We identified small parameter volumes (~3% of the possible volume) in which the model reproduced both dominance distribution and history-dependence of each observer. For 21 of 24 data sets, the identified volumes clustered tightly (~15% of the possible volume), revealing a consistent "operating regime" of multi-stable perception. The "operating regime" turned out to be marginally stable or, equivalently, near the brink of an oscillatory instability. The chance probability of the observed clustering was <0.02. To understand the functional significance of this empirical "operating regime," we compared it to the theoretical "sweet spot" of the model. We computed this "sweet spot" as the intersection of the parameter volumes in which the model produced stable perceptual outcomes and in which it was sensitive to input modulations. Remarkably, the empirical "operating regime" proved to be largely coextensive with the theoretical "sweet spot." This demonstrated that perceptual dynamics was not merely consistent but also functionally optimized (in that it balances stability with sensitivity). Our results imply that multi-stable perception is not a laboratory curiosity, but reflects a functional optimization of perceptual dynamics for visual inference. PMID:23518509

  10. Multi-stable perception balances stability and sensitivity

    PubMed Central

    Pastukhov, Alexander; García-Rodríguez, Pedro E.; Haenicke, Joachim; Guillamon, Antoni; Deco, Gustavo; Braun, Jochen

    2013-01-01

    We report that multi-stable perception operates in a consistent, dynamical regime, balancing the conflicting goals of stability and sensitivity. When a multi-stable visual display is viewed continuously, its phenomenal appearance reverses spontaneously at irregular intervals. We characterized the perceptual dynamics of individual observers in terms of four statistical measures: the distribution of dominance times (mean and variance) and the novel, subtle dependence on prior history (correlation and time-constant). The dynamics of multi-stable perception is known to reflect several stabilizing and destabilizing factors. Phenomenologically, its main aspects are captured by a simplistic computational model with competition, adaptation, and noise. We identified small parameter volumes (~3% of the possible volume) in which the model reproduced both dominance distribution and history-dependence of each observer. For 21 of 24 data sets, the identified volumes clustered tightly (~15% of the possible volume), revealing a consistent “operating regime” of multi-stable perception. The “operating regime” turned out to be marginally stable or, equivalently, near the brink of an oscillatory instability. The chance probability of the observed clustering was <0.02. To understand the functional significance of this empirical “operating regime,” we compared it to the theoretical “sweet spot” of the model. We computed this “sweet spot” as the intersection of the parameter volumes in which the model produced stable perceptual outcomes and in which it was sensitive to input modulations. Remarkably, the empirical “operating regime” proved to be largely coextensive with the theoretical “sweet spot.” This demonstrated that perceptual dynamics was not merely consistent but also functionally optimized (in that it balances stability with sensitivity). Our results imply that multi-stable perception is not a laboratory curiosity, but reflects a functional optimization of perceptual dynamics for visual inference. PMID:23518509

  11. Stable retrograde orbits around the triple system 2001 SN263

    NASA Astrophysics Data System (ADS)

    Araujo, R. A. N.; Winter, O. C.; Prado, A. F. B. A.

    2015-06-01

    The near-Earth Asteroid 2001 SN263 is a triple system of asteroids and it is the target of the ASTER mission - First Brazilian Deep Space Mission. The announcement of this mission has motivated a study aimed to characterize regions of stability of the system. Araujo et al., characterized the stable regions around the components of the triple system for the planar and prograde cases. Through numerical integrations they found that the stable regions are in two tiny internal zones, one of them placed very close to Alpha and another close to Beta, and in the external region. For a space mission aimed to place the probe in the internal region of the system those results do not seem to be very interesting. Therefore, knowing that the retrograde orbits are expected to be more stable, here we present a complementary study. We now considered particles orbiting the components of the system, in the internal and external regions, with relative inclinations between 90° < I ? 180°, i.e. particles with retrograde orbits. Our goal is to characterize the stable regions of the system for retrograde orbits, and then detach a preferred region to place the space probe. For a space mission, the most interesting regions would be those that are unstable for the prograde cases, but stable for the retrograde cases. Such configuration provide a stable region to place the mission probe with a relative retrograde orbit, and, at the same time, guarantees a region free of debris since they are expected to have prograde orbits. We found that in fact the internal and external stable regions significantly increase when compared to the prograde case. For particles with e = 0 and I = 180°, we found that nearly the whole region around Alpha and Beta remain stable. We then identified three internal regions and one external region that are very interesting to place the space probe. We present the stable regions found for the retrograde case and a discussion on those preferred regions. We also discuss the effects of resonances of the particles with Beta and Gamma, and the role of the Kozai mechanism in this scenario. These results help us understand and characterize the stability of the triple system 2001 SN263 when retrograde orbits are considered, and provide important parameters to the design of the ASTER mission.

  12. Development of Stable Influenza Vaccine Powder Formulations: Challenges and Possibilities

    PubMed Central

    Amorij, J-P.; Huckriede, A.; Wilschut, J.; Frijlink, H. W.

    2008-01-01

    Influenza vaccination represents the cornerstone of influenza prevention. However, today all influenza vaccines are formulated as liquids that are unstable at ambient temperatures and have to be stored and distributed under refrigeration. In order to stabilize influenza vaccines, they can be brought into the dry state using suitable excipients, stabilizers and drying processes. The resulting stable influenza vaccine powder is independent of cold-chain facilities. This can be attractive for the integration of the vaccine logistics with general drug distribution in Western as well as developing countries. In addition, a stockpile of stable vaccine formulations of potential vaccines against pandemic viruses can provide an immediate availability and simple distribution of vaccine in a pandemic outbreak. Finally, in the development of new needle-free dosage forms, dry and stable influenza vaccine powder formulations can facilitate new or improved targeting strategies for the vaccine compound. This review represents the current status of dry stable inactivated influenza vaccine development. Attention is given to the different influenza vaccine types (i.e. whole inactivated virus, split, subunit or virosomal vaccine), the rationale and need for stabilized influenza vaccines, drying methods by which influenza vaccines can be stabilized (i.e. lyophilization, spray drying, spray-freeze drying, vacuum drying or supercritical fluid drying), the current status of dry influenza vaccine development and the challenges for ultimate market introduction of a stable and effective dry-powder influenza vaccine. PMID:18338241

  13. STABLE ISOTOPE DYNAMICS IN SUMMER FLOUNDER TISSUES, WITH APPLICATION TO DIETARY ASSESSMENTS IN CHESAPEAKE BAY

    E-print Network

    Newman, Michael C.

    STABLE ISOTOPE DYNAMICS IN SUMMER FLOUNDER TISSUES, WITH APPLICATION TO DIETARY ASSESSMENTS Growth rates........................................................................18 Isotopic turnover 2: STABLE ISOTOPE ANALYSIS OF SUMMER FLOUNDER DIETS IN CHESAPEAKE BAY

  14. Unusually Stable Pyrazolate-Bridged Dialuminum Complexes Containing Bridging Methyl Groups

    E-print Network

    Schlegel, H. Bernhard

    Unusually Stable Pyrazolate-Bridged Dialuminum Complexes Containing Bridging Methyl Groups Zhengkun pyrazoles with excess trimethylaluminum. The bridging methyl groups in these complexes are more stable than

  15. Stable and generalized-t distributions and applications

    NASA Astrophysics Data System (ADS)

    Rathie, P. N.; Coutinho, M.; Sousa, T. R.; Rodrigues, G. S.; Carrijo, T. B.

    2012-12-01

    In this paper a generalized-t distribution is introduced and used as an alternative to the symmetric stable distribution. To do so, the ?2-divergence is presented and minimized to approximate the symmetric stable distribution, as accurately as possible, by the generalized-t distribution. Kth moments for the generalized-t distribution function are given. The stable distribution is defined in terms of generalized hypergeometric functions. Five applications with natural data (sunspots activity), and financial data (stock exchange in Brazil, South Africa and Venezuela, and daily variation of Petrobras stock market) are analyzed. A time series analysis is used to eliminate data correlation in each data set, and then the distributions are used to fit the residuals of these models.

  16. Results of the Stable Microgravity Vibration Isolation Flight Experiment

    NASA Technical Reports Server (NTRS)

    Edberg, Donald; Boucher, Robert; Schenck, David; Nurre, Gerald; Whorton, Mark; Kim, Young; Alhorn, Dean

    1996-01-01

    This paper presents an overview of the STABLE microgravity isolation system developed and successfully flight tested in October 1995. A description of the hardware design and operational principles is given. A sample of the measured flight data is presented, including an evaluation of attenuation performance provided by the actively controlled electromagnetic isolation system. Preliminary analyses of flight data show that the acceleration environment aboard STABLE's isolated platform was attenuated by a factor of more than 25 between 0.1 and 100 Hz. STABLE was developed under a cooperative agreement between National Aeronautics and Space Administration, Marshall Space Flight Center, and McDonnell Douglas Aerospace. The flight hardware was designed, fabricated, integrated, tested, and delivered to the Cape during a five month period.

  17. Stable hydrogenated graphene edge types: Normal and reconstructed Klein edges

    NASA Astrophysics Data System (ADS)

    Wagner, Philipp; Ivanovskaya, Viktoria V.; Melle-Franco, Manuel; Humbert, Bernard; Adjizian, Jean-Joseph; Briddon, Patrick R.; Ewels, Christopher P.

    2013-09-01

    Hydrogenated graphene edges are assumed to be either armchair, zigzag, or a combination of the two. We show that the zigzag is not the most stable fully hydrogenated edge structure along the <21¯1¯0> direction. Instead hydrogenated Klein and reconstructed Klein based edges are found to be energetically more favorable, with stabilities approaching that of armchair edges. These new structures “unify” graphene edge topology, the most stable flat hydrogenated graphene edges always consisting of pairwise bonded C2H4 edge groups, irrespective of the edge orientation. When edge rippling is included, CH3 edge groups are most stable. These new fundamental hydrogen-terminated edges have important implications for graphene edge imaging and spectroscopy, as well as mechanisms for graphene growth, nanotube cutting, and nanoribbon formation and behavior.

  18. Free electron lasers using stable-unstable ring resonators

    SciTech Connect

    Schmitt, M.J.; Paxton, A.H.

    1989-01-01

    The free electron laser (FEL) simulation code FELEX is used to examine the operation of stable-unstable FEL resonators. These resonators are stable along one transverse axis and unstable along the orthogonal transverse axis. The simulations utilize a ring resonator with an intracavity focus in the unstable plane near the center of the wiggler (close to the same axial position as the waist in the stable plane) thereby enhancing the coupling between the optical and electron beams. Asymmetric output scraping is performed in the back leg of the ring using a reflective mirror inserted from one side of the unstable axis. Resonators with relatively low equivalent Fresnel number (/vert bar/N/sub eq//vert bar/ less than or equal to 10) and magnification (/vert bar/M/sub x//vert bar/ approx. = 1.2) are examined. Optical characteristics including the cavity mode profile at various positions inside the resonator are shown. 8 refs., 8 figs.

  19. On the genealogy on conditioned stable L\\'evy forest

    E-print Network

    Chaumont, Loic

    2007-01-01

    We give a realization of the stable L\\'evy forest of a given size conditioned by its mass from the path of the unconditioned forest. Then, we prove an invariance principle for this conditioned forest by considering $k$ independent Galton-Watson trees whose offspring distribution is in the domain of attraction of any stable law conditioned on their total progeny to be equal to $n$. We prove that when $n$ and $k$ tend towards $+\\infty$, under suitable rescaling, the associated coding random walk, the contour and height processes converge in law on the Skorokhod space respectively towards the "first passage bridge" of a stable L\\'evy process with no negative jumps and its height process.

  20. Fractional Lévy stable motion can model subdiffusive dynamics

    NASA Astrophysics Data System (ADS)

    Burnecki, Krzysztof; Weron, Aleksander

    2010-08-01

    We show in this paper that the sample (time average) mean-squared displacement (MSD) of the fractional Lévy ? -stable motion behaves very differently from the corresponding ensemble average (second moment). While the ensemble average MSD diverges for ?<2 , the sample MSD may exhibit either subdiffusion, normal diffusion, or superdiffusion. Thus, H -self-similar Lévy stable processes can model either a subdiffusive, diffusive or superdiffusive dynamics in the sense of sample MSD. We show that the character of the process is controlled by a sign of the memory parameter d=H-1/? . We also introduce a sample p -variation dynamics test which allows to distinguish between two models of subdiffusive dynamics. Finally, we illustrate a subdiffusive behavior of the fractional Lévy stable motion on biological data describing the motion of individual fluorescently labeled mRNA molecules inside live E. coli cells, but it may concern many other fields of contemporary experimental physics.

  1. Stable and Metastable Cosmic Strings in Heterotic M-Theory

    E-print Network

    Evgeny I. Buchbinder

    2006-06-03

    We address the question of finding stable and metastable cosmic strings in quasi-realistic heterotic M-theory compactifications with stabilized moduli. According to Polchinski's conjecture, the only stable strings in the absence of massless fields are Aharonov-Bohm strings. Such strings could potentially be created in heterotic compactifications as bound states of open membranes, five-branes wrapped on four-cycles and solitonic strings. However, in generic compactifications, the process of moduli stabilization can conflict production of Aharanov-Bohm strings. In this case, heterotic cosmic strings will have to be unstable under breakage on monopoles. We estimate the monopole masses and find that they are big enough so that the strings can be metastable with a sufficiently long lifetime. On the other hand, if we allow one or more axions to remain massless at low energies, stable global strings can be produced.

  2. Stable Isotope Ratios as Biomarkers of Diet for Health Research.

    PubMed

    O'Brien, Diane M

    2015-07-17

    Diet is a leading modifiable risk factor for chronic disease, but it remains difficult to measure accurately due to the error and bias inherent in self-reported methods of diet assessment. Consequently, there is a pressing need for more objective biomarkers of diet for use in health research. The stable isotope ratios of light elements are a promising set of candidate biomarkers because they vary naturally and reproducibly among foods, and those variations are captured in molecules and tissues with high fidelity. Recent studies have identified valid isotopic measures of short- and long-term sugar intake, meat intake, and fish intake in specific populations. These studies provide a strong foundation for validating stable isotopic biomarkers in the general US population. Approaches to improve specificity for specific foods are needed; for example, by modeling intake using multiple stable isotope ratios or by isolating and measuring specific molecules linked to foods of interest. PMID:26048703

  3. Intermittent Turbulence in the Very Stable Ekman Layer

    SciTech Connect

    Barnard, James C.

    2001-01-05

    INTERMITTENT TURBULENCE IN THE VERY STABLE EKMAN LAYER This study describes a Direct Numerical Simulation (DNS) of a very stable Ekman layer in which a constant downward heat flux is applied at the lower boundary, thus cooling the fluid above. Numerical experiments were performed in which the strength of the imposed heat flux was varied. For downward heat fluxes above a certain critical value the turbulence becomes intermittent and, as the heat flux increases beyond this value, the flow tends to relaminarize because of the very strong ambient stratification. We adopt Mahrt?s (1999) definition of the very stable boundary layer as a boundary layer in which intermittent, rather than continuous turbulence, is observed. Numerical experiments were used to test various hypothesis of where in ?stability parameter space? the very stable boundary layer is found. These experiments support the findings of Howell and Sun (1999) that the boundary layer will exhibit intermittency and therefore be categorized as ?very stable?, when the stability parameter, z/L, exceeds unity. Another marker for the very stable boundary layer, Derbyshire?s (1990) maximum heat flux criterion, was also examined. Using a case study drawn from the simulations where turbulence intermittency was observed, the mechanism that causes the intermittence was investigated. It was found that patchy turbulence originates from a vigorous inflectional, Ekman-like instability -- a roll cell -- that lifts colder air over warmer air. The resulting convective instability causes an intense burst of turbulence. This turbulence is short-lived because the lifting motion of the roll cell, as well as the roll cell itself, is partially destroyed after the patchy turbulence is generated. Examples of intermittent turbulence obtained from the simulations appear to be consistent with observations of intermittency even though the Reynolds number of the DNS is relatively low (400).

  4. A weakly stable algorithm for general Toeplitz systems

    E-print Network

    Bojanczyk, Adam W; de Hoog, Frank R

    2010-01-01

    We show that a fast algorithm for the QR factorization of a Toeplitz or Hankel matrix A is weakly stable in the sense that R^T.R is close to A^T.A. Thus, when the algorithm is used to solve the semi-normal equations R^T.Rx = A^Tb, we obtain a weakly stable method for the solution of a nonsingular Toeplitz or Hankel linear system Ax = b. The algorithm also applies to the solution of the full-rank Toeplitz or Hankel least squares problem.

  5. On the existence of stable seasonally varying Arctic sea ice

    E-print Network

    Moon, W

    2012-01-01

    Within the framework lower order thermodynamic theories for the climatic evolution of Arctic sea ice we isolate the conditions required for the existence of stable seasonally-varying ice states. This is done by constructing a two-season model from the continuously evolving theory of Eisenman and Wettlaufer (2009) and showing that the necessary and sufficient condition for stable seasonally-varying states resides in the relaxation of the constant annual average short-wave radiative forcing. This forcing is examined within the scenario of greenhouse gas warming, as a function of which stability conditions are discerned.

  6. Next Generation JPL Ultra-Stable Trapped Ion Atomic Clocks

    NASA Technical Reports Server (NTRS)

    Burt, Eric; Tucker, Blake; Larsen, Kameron; Hamell, Robert; Tjoelker, Robert

    2013-01-01

    Over the past decade, trapped ion atomic clock development at the Jet Propulsion Laboratory (JPL) has focused on two directions: 1) new atomic clock technology for space flight applications that require strict adherence to size, weight, and power requirements, and 2) ultra-stable atomic clocks, usually for terrestrial applications emphasizing ultimate performance. In this paper we present a new ultra-stable trapped ion clock designed, built, and tested in the second category. The first new standard, L10, will be delivered to the Naval Research Laboratory for use in characterizing DoD space clocks.

  7. Fiber Optic Cable Thermal Preparation to Ensure Stable Operation

    NASA Technical Reports Server (NTRS)

    Thoames Jr, William J.; Chuska, Rick F.; LaRocca, Frank V.; Switzer, Robert C.; Macmurphy, Shawn L.; Ott, Melanie N.

    2008-01-01

    Fiber optic cables are widely used in modern systems that must provide stable operation during exposure to changing environmental conditions. For example, a fiber optic cable on a satellite may have to reliably function over a temperature range of -50 C up to 125 C. While the system requirements for a particular application will dictate the exact method by which the fibers should be prepared, this work will examine multiple ruggedized fibers prepared in different fashions and subjected to thermal qualification testing. The data show that if properly conditioned the fiber cables can provide stable operation, but if done incorrectly, they will have large fluctuations in transmission.

  8. Synthesis and investigation of stable copper nanoparticle colloids

    NASA Astrophysics Data System (ADS)

    Tyurnina, A. E.; Shur, V. Ya.; Kozin, R. V.; Kuznetsov, D. K.; Pryakhina, V. I.; Burban, G. V.

    2014-07-01

    The synthesis of stable nanoparticle colloids by laser ablation of the copper target in water and fragmentation of Cu + CuO nanopowder with pulsed fiber laser irradiation with a wavelength of 1064 nm and pulse duration of 100 ns has been investigated experimentally. The influence of the technological parameters on the nanoparticle size and stability of the colloid has been studied. It has been shown that the laser ablation creates the CuO spherical nanoparticles. Subsequent fragmentation makes it possible to reduce the nanoparticle size in a colloid and to produce a stable colloidal solution from an aqueous suspension of Cu + CuO nanopowder.

  9. Escape from bounded domains driven by multivariate ?-stable noises

    NASA Astrophysics Data System (ADS)

    Szczepaniec, Krzysztof; Dybiec, Bart?omiej

    2015-06-01

    In this paper we provide an analysis of a mean first passage time problem of a random walker subject to a bivariate ?-stable Lévy-type noise from a 2-dimensional disk. For an appropriate choice of parameters the mean first passage time reveals non-trivial, non-monotonous dependence on the stability index ? describing jumps' length asymptotics both for spherical and Cartesian Lévy flights. Finally, we study escape from a d-dimensional hypersphere showing that a d-dimensional escape process can be used to discriminate between various types of multivariate ?-stable noises, especially spherical and Cartesian Lévy flights.

  10. Properties of ?-stable neutron star matter with hyperons

    E-print Network

    I. Vidaña; A. Polls; A. Ramos; Oe. Elgaroey; L. Engvik; M. Hjorth-Jensen

    1999-12-08

    We present results from many-body calculations for \\beta-stable neutron star matter with nucleonic and hyperonic degrees of freedom, employing the most recent parametrizations of the baryon-baryon interaction of the Nijmegen group. It is found that the only strange baryons emerging in \\beta-stable matter up to total baryonic densities of 1.2 fm^{-3} are \\Sigma^- and \\Lambda. The corresponding equations of state are thence used to compute properties of neutron stars such as the masses, moments of inertia and radii. We also study the possibility of forming a hyperon superfluid and discuss its implications for neutron stars.

  11. Thermally stable surfactants and compositions and methods of use thereof

    SciTech Connect

    Chaiko, David J. (Woodridge, IL)

    2008-09-02

    There are provided novel thermally stable surfactants for use with fillers in the preparation of polymer composites and nanocomposites. Typically, surfactants of the invention are urethanes, ureas or esters of thiocarbamic acid having a hydrocarbyl group of from 10 to 50 carbons and optionally including an ionizable or charged group (e.g., carboxyl group or quaternary amine). Thus, there are provided surfactants having Formula I: ##STR00001## wherein the variables are as defined herein. Further provided are methods of making thermally stable surfactants and compositions, including composites and nanocomposites, using fillers coated with the surfactants.

  12. Remarks on search methods for stable, massive, elementary particles

    NASA Astrophysics Data System (ADS)

    Perl, Martin L.

    2001-11-01

    This paper was presented at the 69th birthday celebration of Professor Eugene Commins, honoring his research achievements. These remarks are about the experimental techniques used in the search for new stable, massive particles, particles at least as massive as the electron. A variety of experimental methods such as accelerator experiments, cosmic ray studies, searches for halo particles in the galaxy and searches for exotic particles in bulk matter are described. A summary is presented of the measured limits on the existence of new stable, massive particle. .

  13. Stable polarization-encoded quantum key distribution in fiber

    E-print Network

    Guang Wu; Jie Chen; Yao Li; Heping Zeng

    2006-06-13

    Polarizations of single-photon pulses have been controlled with long-term stability of more than 10 hours by using an active feedback technique for auto-compensation of unpredictable polarization scrambling in long-distance fiber. Experimental tests of long-term operations in 50, 75 and 100 km fibers demonstrated that such a single-photon polarization control supported stable polarization encoding in long-distance fibers to facilitate stable one-way fiber system for polarization-encoded quantum key distribution, providing quantum bit error rates below the absolute security threshold.

  14. Pedestrian detection based on maximally stable extremal regions

    Microsoft Academic Search

    Vadim Frolov; F. P. Leon

    2010-01-01

    This paper presents a new approach to generate hypotheses about the presence of pedestrians in an infrared image. Information about maximally stable extremal regions is used to locate the warmest regions on the image, which are considered to be potential human heads. To capture the complete human body, these regions are scaled based on the range data of a lidar

  15. Stable isotopes sales: Mound customer and shipment summaries, FY 1985

    SciTech Connect

    Flayler, K.A. (comp.)

    1987-12-15

    A listing is given of Mound's sales of stable isotopes of noble gases, deuterium, carbon, oxygen, nitrogen, chlorine, bromine, and sulfur for fiscal year 1985. Purchasers are listed alphabetically and are divided into domestic and foreign groups. A cross-reference index by location is included for domestic and foreign customers. Cross-reference listings by isotope purchased are included for all customers.

  16. Stable isotope sales: Mound customer and shipment summaries, FY 1986

    SciTech Connect

    Kramer, L.R. (ed.); Flayler, K.A. (comp.)

    1988-05-20

    A listing is given of Mound's sales of stable isotopes of noble gases, carbon, oxygen, nitrogen, chlorine, and sulfur for fiscal year 1986. Purchasers are listed alphabetically and are divided into domestic and foreign groups. Cross-reference indexes by location and by isotope are included for all customers. 3 tabs.

  17. Stable isotope composition of the meteoric precipitation in Croatia.

    PubMed

    Hunjak, Tamara; Lutz, Hans O; Roller-Lutz, Zvjezdana

    2013-01-01

    The precipitation is the input into the water system. Its stable isotope composition has to be known for the proper use and management of water resources. Croatia is not well represented in the Global Network of Isotopes in Precipitation (GNIP) database, and the geomorphology of the country causes specific local conditions. Therefore, at the Stable Isotope Laboratory (SILab), Rijeka, we monitor the stable isotope composition (?(18)O, ?(2)H) of precipitation. Since ?(18)O and ?(2)H are well correlated, we concentrate the discussion on the ?(18)O distribution. Together with GNIP, our database contains 40 stations in Croatia and in the neighbouring countries. Their different latitudes, longitudes and altitudes give information of great detail, including the influence of the topographic structure on the precipitation in the south-eastern part of Europe, as well as the complex interplay of the different climate conditions in the area. Within a few hundred kilometres, the stable isotope values display a significant change from the maritime character in the south (mean ?(18)O around-6 to-8‰) to the continental behaviour in the north (mean ?(18)O around-8 to-11‰). Depending on the location, the mean ?(18)O values vary with altitude at a rate of approximately-0.2‰/100 m and-0.4‰/100 m, respectively. Also the deuterium excess has been found to depend on location and altitude. The data are being used to construct a ?(18)O map for the entire area. PMID:23937110

  18. Pre-stressed Morphing Bistable and Neutrally Stable Shells

    E-print Network

    Guest, Simon

    Pre-stressed Morphing Bistable and Neutrally Stable Shells Keith A. Seffen Senior Lecturer-stressed shells, which are capable of "morphing" under large deflexions between very different load coiling. These shells demonstrate simple morphing structures, which can be used to create effective shape

  19. Superradiantly stable non-extremal Reissner-Nordstrom black holes

    E-print Network

    Jia-Hui Huang; Zhan-Feng Mai

    2015-03-04

    The superradiant stability is investigated for non-extremal Reissner-Nordstrom black hole. We use an algebraic method to demonstrate that all non-extremal Reissner-Nordstrom black holes are superradiantly stable against a charged massive scalar perturbation. This improves the results obtained before for non-extremal Reissner-Nordstrom black holes.

  20. Stable and unbiased flow turbulence estimation from pulse echo ultrasound

    Microsoft Academic Search

    Yi Zheng; James F. Greenleaf

    1999-01-01

    A new method for stable and unbiased flow turbulence estimation has been developed for medical ultrasonic color flow imaging. Conventional turbulence estimates from a finite number of transmitted pulses could be biased, unreliable, and erroneous. We found that a conventional method cannot provide quantitative estimates of variance of flow velocity. We propose a new approach for flow turbulence estimation that

  1. The Evolutionarily Stable Exploitation of a Renewing Resource

    Microsoft Academic Search

    Alasdair I. Houston; John M. McNamara; James N. Webb

    1995-01-01

    The evolutionary stable distribution of animals between two sources of food is considered. At one source (the “fixed” source), food is obtained at a fixed rate, regardless of the number of animals present and the time since the source was used. At the other source (the “renewing” source) the probability that an item of food is present depends on the

  2. BaC: a thermodynamically stable layered superconductor.

    PubMed

    Wang, Dian-Hui; Zhou, Huai-Ying; Hu, Chao-Hao; Oganov, Artem R; Zhong, Yan; Rao, Guang-Hui

    2014-10-14

    To predict all stable compounds in the Ba-C system, we perform a comprehensive study using first-principles variable-composition evolutionary algorithm USPEX. We find that at 0 K the well-known compound BaC2 is metastable in the whole pressure range 0-40 GPa, while intercalated graphite phase BaC6 is stable at 0-19 GPa. A hitherto unknown layered orthorhombic Pbam phase of BaC has structure consisting of alternating layers of Ba atoms and layers of stoichiometry Ba2C3 containing linear C3 groups and is predicted to be stable in the pressure range 3-32 GPa. From our electron-phonon coupling calculations, the newly found BaC compound is a phonon-mediated superconductor and has a critical superconductivity temperature Tc of 4.32 K at 5 GPa. This compound is dynamically stable at 0 GPa and therefore may be quenchable under normal conditions. PMID:25163859

  3. FILTRATION ASSOCIATED TO TORSION SEMI-STABLE REPRESENTATIONS

    E-print Network

    Liu, Tong

    FILTRATION ASSOCIATED TO TORSION SEMI-STABLE REPRESENTATIONS TONG LIU Abstract. Let p be an odd prime, K a finite extension of Qp and G := Gal(Qp/K) the Galois group. We construct and study filtration type. 1 Contents 1. Introduction 2 2. Filtration encoded in p-adic Hodge data 3 2.1. Preliminary

  4. FILTRATION ASSOCIATED TO TORSION SEMI-STABLE REPRESENTATIONS

    E-print Network

    Liu, Tong

    FILTRATION ASSOCIATED TO TORSION SEMI-STABLE REPRESENTATIONS TONG LIU Abstract. Let p be an odd prime, K a finite extension of Qp and G := Gal(Qp/K) the Galois group. We construct and study filtration-adic Hodge-Tate type. 1 Contents 1. Introduction 2 2. Filtration encoded in p-adic Hodge data 3 2

  5. A combinatorial algorithm for weighted stable sets in bipartite graphs

    Microsoft Academic Search

    Ulrich Faigle; Gereon Frahling

    2006-01-01

    Computing a maximum weighted stable set in a bipartite graph is considered well- solved and usually approached with preflow-push, Ford-Fulkerson or network simplex algorithms. We present a combinatorial algorithm for the problem that is not based on flows. Numerical tests suggest that this algorithm performs quite well in practice and is competitive with flow based algorithms especially in the case

  6. FREE ABELIAN COVERS, SHORT LOOPS, STABLE LENGTH, AND SYSTOLIC INEQUALITIES

    E-print Network

    FREE ABELIAN COVERS, SHORT LOOPS, STABLE LENGTH, AND SYSTOLIC torus H1(X; R)=H1(X; Z)R. App* *lying M. Gromov's filling inequality to the typical fiber of f, we prove an int* *erpolating inequality for two flavors of shortest length invariants of loops

  7. Stable isotope ecology in the Omo-Turkana Basin.

    PubMed

    Cerling, Thure E; Levin, Naomi E; Passey, Benjamin H

    2011-01-01

    Stable isotopes provide an independent assessment of paleoenvironments in the Omo-Turkana Basin. Stable isotopes track the flow of oxygen and carbon through ecosystems and accordingly are not directly related to changes in mammalian faunal composition or sedimentology. Therefore, isotope studies give insight into the paleoenvironmental conditions in which human evolutionary trends have been recorded. The development of stable isotopes as indicators of continental environmental conditions has proceeded in parallel with questions about the conditions of human environment. What was the vegetation? How hot was it? How dry? What were the diets of animals living among early humans? And most persistently, how important were "savannas" to early hominids? In this review, we take the opportunity to provide extensive background on the use of isotopes in anthropological sites. The application of stable isotope ecology to anthropological sites in the Turkana Basin has a long history, but in many ways the Omo-Turkana Basin has been a proving ground for the development of new proxy methods for understanding tropical terrestrial environments in the Neogene and Quaternary. For that reason, we also describe some of the fundamental aspects of isotope ecology that developed outside the field of paleoanthropology. PMID:22170692

  8. Stable Gene Selection from Microarray Data via Sample Weighting

    E-print Network

    Yu, Lei

    Stable Gene Selection from Microarray Data via Sample Weighting Lei Yu, Yue Han, and Michael E. Berens Abstract--Feature selection from gene expression microarray data is a widely used technique for selecting candidate genes in various cancer studies. Besides predictive ability of the selected genes

  9. Degenerate and Stable Yang-Mills-Higgs Pairs

    E-print Network

    Zhi Hu; Sen Hu

    2015-02-09

    In this paper, we introduce some notions on the pair consisting of a Chern connection and a Higgs field closely related to the first and second variation of Yang-Mills- Higgs functional, such as strong Yang-Mills-Higgs pair, degenerate Yang-Mills-Higgs pair, stable Yang-Mills-Higgs pair. We investigate some properties of such pairs.

  10. Calculations predict a stable molecular crystal of N8

    E-print Network

    Krylov, Anna I.

    nitrogen solid, including at low pressure (below 20 GPa). The structure and properties of the N8 molecular nitrogen species8­13 . A major motivation for this pursuit is that polynitrogen molecules are expected is the most stable below 170 GPa (ref. 16). Among the high-pressure phases, at pressures below 47 GPa

  11. TECHNICAL ADVANCE Stable integration of an engineered megabase repeat array

    E-print Network

    Parrott, Wayne

    sequence into plant genomes. Here we show that it is possible to synthetically engineer and introduce 2011. * For correspondence (fax +1 706 542 1805; e-mail kelly@plantbio.uga.edu). SUMMARY Plant genomeTECHNICAL ADVANCE Stable integration of an engineered megabase repeat array into the maize genome

  12. Computational Predictions of Stable 2D Arrays of Bidisperse Particles

    E-print Network

    () of 0.375. We found that interparticle forces were essential to stabilize the LS (the two-dimensional NaCl-stabilized gold particles with distinct bimodal size distributions spontaneously order into twoComputational Predictions of Stable 2D Arrays of Bidisperse Particles Brooks D. Rabideau and Roger

  13. UV Stable High Birefringence Liquid Crystals Sebastian GAUZA

    E-print Network

    Wu, Shin-Tson

    UV Stable High Birefringence Liquid Crystals Sebastian GAUZA Ã , Chien-Hui WEN, Bijun TAN and Shin March 20, 2004; accepted July 9, 2004; published October 8, 2004) High birefringence and low viscosity. Excellent UV durability of some of the single high birefringence isothiocyanianes was discovered. The new

  14. Simulation of thermally stable chamber designed for testing LTCC structures

    Microsoft Academic Search

    A. Bienkowski; P. Bembnowicz; H. Roguszczak; L. J. Golonka

    2008-01-01

    A chamber providing thermally stable environment for LTCC (Low Temperature Co-fired Ceramics) structures testing is designed and fabricated. Such device can be applied in a wide range of preliminary testing stages of the LTCC based Microsystems, especially microfluidic one. The aim is to obtain good temperature uniformity and stability. A steady state thermal simulation is done and evaluated with infrared

  15. ABSORPTION CROSS SECTION OF STABLE, LOW CROSS SECTION FISSION PRODUCTS

    Microsoft Academic Search

    Breslauer

    1959-01-01

    A record of the relatively stable, low cross section fissibn products ; available on ANP nuclear data tape is presented for conventional reactor ; calculations. The record is based on data included in the Geneva conference ; paper by Gordeev and Pupko. The label slag is applied to fission products. ; (J.R.D.);

  16. Compressive Sensing for Ultrasound RF Echoes Using -Stable Distributions

    E-print Network

    Tsakalides, Panagiotis

    is arguably the most widely used cross-sectional medical imaging modality worldwide. In- deed, ultrasound hasCompressive Sensing for Ultrasound RF Echoes Using -Stable Distributions Alin Achim, Benjamin or orthogonal matching pursuit, both visually and in terms of PSNR. I. INTRODUCTION Ultrasound imaging

  17. Stable Dynamics of Sand Automata Alberto Dennunzio1

    E-print Network

    Paris-Sud XI, Université de

    Stable Dynamics of Sand Automata Alberto Dennunzio1 , Pierre Guillon2 , and Benoît Masson3 1.masson@lif.univ-mrs.fr Abstract. In this paper, we study different notions of stability of sand automata, dynamical systems systems [10]. In [3], the authors introduced sand automata as a generalization of sandpile models

  18. Weights in stable marriage problems increase manipulation opportunities

    E-print Network

    Rossi, Francesca

    Weights in stable marriage problems increase manipulation opportunities Maria Silvia Pini University of Padova Padova, Italy mpini@math.unipd.it Francesca Rossi University of Padova Padova, Italy frossi@math.unipd.it Kristen Brent Venable University of Padova Padova, Italy kvenable@math.unipd.it Toby

  19. Procedural Fairness in Stable Marriage Problems (Extended Abstract)

    E-print Network

    Walsh, Toby

    Procedural Fairness in Stable Marriage Problems (Extended Abstract) Mirco Gelain University of Padova, Italy mgelain@math.unipd.it Maria Silvia Pini University of Padova, Italy mpini@math.unipd.it Francesca Rossi University of Padova, Italy frossi@math.unipd.it Kristen Brent Venable Universita' di Padova

  20. Pollen as a tool for tracking stable flies.

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The stable fly, (Stomoxys calcitrans L.), is an important pest of humans and livestock in many parts of the world. Its immature stages develop in decaying vegetation, e.g. hya, silage, feed, mulch and grass clippings, in agricultural and urban areas. although both sexes are oligate blood feeders, ...

  1. Stable Isotope Evidence of Diet at Neolithic Çatalhöyük, Turkey

    Microsoft Academic Search

    M. P. Richards; J. A. Pearson; T. I. Molleson; N. Russell; L. Martin

    2003-01-01

    We report here new evidence for human subsistence from stable isotope analysis of humans and fauna from Catalhöyük. The analyses complement other lines of subsistence evidence, and indicate that, contrary to the original excavator James Mellaart's assertion (Mellaart, 1975), cattle was unlikely to have been the main source of dietary protein for all occupants. The analyses have also indicated the

  2. Stable adaptive control using fuzzy systems and neural networks

    Microsoft Academic Search

    J. T. Spooner; K. M. Passino

    1996-01-01

    Stable direct and indirect adaptive controllers are presented, which use Takagi-Sugeno fuzzy systems, conventional fuzzy systems, or a class of neural networks to provide asymptotic tracking of a reference signal for a class of continuous-time nonlinear plants with poorly understood dynamics. The indirect adaptive scheme allows for the inclusion of a priori knowledge about the plant dynamics in terms of

  3. Neutron Stimulated Emission Computed Tomography of Stable Isotopes

    E-print Network

    Neutron Stimulated Emission Computed Tomography of Stable Isotopes Carey E. Floyd Jr.*ab , Calvin North Carolina Keywords: imaging, neutrons, tomography, spectroscopy ABSTRACT Here we report on the development of a new molecular imaging technique using inelastic scattering of fast neutrons. Earlier studies

  4. USE OF STABLE ISOTOPES IN ENVIRONMENTAL AND FORENSIC GEOCHEMISTRY STUDIES

    EPA Science Inventory

    Stable carbon and hydrogen isotopes have been used for many decades in the petroleum industry, but the development of combined gas chromatography-isotope ratio mass spectrometry (GCIRMS) has led to a virtual explosion in application of this technique not only in petroleum explora...

  5. Possible Potentials Responsible for Stable Circular Relativistic Orbits

    ERIC Educational Resources Information Center

    Kumar, Prashant; Bhattacharya, Kaushik

    2011-01-01

    Bertrand's theorem in classical mechanics of the central force fields attracts us because of its predictive power. It categorically proves that there can only be two types of forces which can produce stable, circular orbits. In this paper an attempt has been made to generalize Bertrand's theorem to the central force problem of relativistic…

  6. Ball lightning explained as a stable plasma toroid

    Microsoft Academic Search

    Clint Seward; Chiping Chen; Ken Ware

    2001-01-01

    Spinning plasma toroids are created using high power electric arcs similar to lightning bolts. The spinning toroids are observed to be stable in atmosphere with no confining magnetic fields. Spinning toroids have the appearance of spheres, or balls, and create bright light through collisions with neutrals in the atmosphere. The spinning toroids are observed to last for more than 200

  7. Ball lightning explained as a stable plasma toroid

    Microsoft Academic Search

    C. Seward

    2001-01-01

    Summary form only given, as follows. Describes spinning plasma toroids that are created using high power electric arcs similar to lightning bolts. The spinning toroids are observed to be stable in atmosphere with no confining magnetic fields. Spinning toroids have the appearance of spheres, or balls, and create bright light through collisions with neutrals in the atmosphere. The spinning toroids

  8. Multifractal analysis and ?-stable processes: a methodological contribution

    Microsoft Academic Search

    Pierre Chainais; Patrice Abry; Darryl Veitch

    2000-01-01

    This work is a contribution to the analysis of the procedure, based on wavelet coefficient partition functions, commonly used to estimate the Legendre multifractal spectrum. The procedure is applied to two examples, a fractional Brownian motion in multifractal time and a self-similar ?-stable process, whose sample paths exhibit irregularities that by eye appear very close. We observe that, for the

  9. Nonlinear flexures for stable deflection of an electrostatically actuated micromirror

    Microsoft Academic Search

    David M. Burns; Victor M. Bright

    1997-01-01

    This paper describes how nonlinear force flexures can be used to increase the stable deflection distance of an electrostatically operated micromirror. Traditional micromirrors have flexures that provide linear force as a function of deflection. Electrostatic attraction is a nonlinear force, so after a traditional micromirror has deflected one-third of the initial separation distance between the top and bottom electrode, the

  10. AN ASYMPTOTICALLY STABLE SCHEME FOR DIFFUSIVE COAGULATION-FRAGMENTATION MODELS

    E-print Network

    Filbet, Francis

    AN ASYMPTOTICALLY STABLE SCHEME FOR DIFFUSIVE COAGULATION-FRAGMENTATION MODELS FRANCIS FILBET Abstract. This paper is devoted to the analysis of a numerical scheme for the coagulation and fragmentation of the space nonhomogeneous coagulation-fragmentation model. It is shown that the scheme preserves positivity

  11. Completing the missing data in markov symmetric stable time series

    Microsoft Academic Search

    S. N. Moiseev

    2000-01-01

    Optimal algorithms for completing the missing data in Markov symmetric stable time series are proposed. We consider the cases\\u000a where the data missing is caused by either a mechanism that is independent of the series values or a random censoring from\\u000a below. The completing does not distort the probability properties of the series.

  12. Fluid and Air-Stable Lipopolymer Membranes for Biosensor Applications

    E-print Network

    was pulled through the air/water interface, the bilayer remained intact on the surface and a thin water film in the presence of humid air as well as when it was reintroduced to bulk water. Unfortunately, such a systemFluid and Air-Stable Lipopolymer Membranes for Biosensor Applications Fernando Albertorio, Arnaldo

  13. Stable Isotopic Constraints of the Turpan Basin in Northwestern China

    Microsoft Academic Search

    A. J. Schaen

    2010-01-01

    Stable isotopic analysis of sedimentary rocks can be used to reconstruct past geologic changes in the elevation and climate of topographic features such as mountain ranges and plateaus. The Tibetan Plateau is an ideal field laboratory for conducting this type of study because of the Plateau's extreme topographic relief and relatively recent geologic growth. Here we present oxygen and carbon

  14. Creating ultra-compact binaries through stable mass transfer

    E-print Network

    van der Sluys, Marc

    Creating ultra-compact binaries through stable mass transfer M.V. van der Sluys , F. Verbunt and O in which a slightly evolved star starts mass transfer to a neutron star can evolve towards ultra­40 minutes within the Hubble time. We show that only small ranges of initial periods and masses lead to ultra

  15. Generating thermal stable variants of protein domains through phage display.

    PubMed

    Pershad, Kritika; Kay, Brian K

    2013-03-15

    Often in protein design research, one desires to generate thermally stable variants of a protein or domain. One route to identifying mutations that yield domains that remain folded and active at a higher temperature is through the use of directed evolution. A library of protein domain variants can be generated by mutagenic PCR, expressed on the surface of bacteriophage M13, and subjected to heat, such that the unfolded forms of the domain, showing reduced or no binding activity, are lost during subsequent affinity selection, whereas variants that still retain binding to their target are selected and enriched with each subsequent round of affinity selection. This approach takes advantage of the fact that bacteriophage M13 particles are heat stable and resistant to many proteases and protein denaturants. We present the application of this general approach to generating thermally stable variants of a eukaryotic peptide-binding domain. The benefits of producing such variants are that they typically express at high levels in Escherichia coli (30-60 mg/L shake flask) and remain soluble in solution at higher concentrations for longer periods of time than the wild-type form of the domain. The process of library generation and screening generally requires about one month of effort, and yields variants with >10 °C increase in thermal stability, as measured in a simple fluorescence-based thermal shift assay. It is anticipated that thermally stable variants will serve as excellent scaffolds for generating affinity reagents to a variety of targets of interest. PMID:23276752

  16. Palaeoclimate interpretation of stable isotope data from lake sediment archives

    Microsoft Academic Search

    Melanie J Leng; Jim D Marshall

    2004-01-01

    The isotope composition of authigenic and biogenic carbonates and diatom silica are commonly used as palaeoclimate proxies from lake sediments. This article reviews the controls on the isotope composition of lacustrine skeletal and non-skeletal deposits and illustrates how stable isotope studies contribute to an understanding of changes in temperature, precipitation patterns, evaporation and the carbon cycle. It highlights the differences

  17. Stable explicit schemes for equations of Schroedinger type

    NASA Technical Reports Server (NTRS)

    Mickens, Ronald E.

    1989-01-01

    A method for constructing explicit finite-difference schemes which can be used to solve Schroedinger-type partial-differential equations is presented. A forward Euler scheme that is conditionally stable is given by the procedure. The results presented are based on the analysis of the simplest Schroedinger type equation.

  18. Connected 4-dimensional stable planes with many central collineations

    Microsoft Academic Search

    Hans-Peter Seidel

    1990-01-01

    This paper gives a complete classification of all connected 4-dimensional stable planes with the property that every point is the centre of a non-trivial central collineation. It is shown that under these assumptions the automorphism group has an open orbit on the point space. This implies the existence of an open subplane that carries the additional structure of a generalized

  19. UNCORRECTED 2 Towards stable coupling methods for high-order

    E-print Network

    Yosibash, Zohar

    UNCORRECTED PROOF 1 2 Towards stable coupling methods for high-order 3 discretization of fluid­structure the fluid to the structure. A 18 subsonic three-dimensional compressible flow over an elastic non dimensional structural simulation of very thin 36 structures without a priori modeling assumptions

  20. 3D hypercycles have no stable spatial structure

    Microsoft Academic Search

    Mikael B. Cronhjort; Anna M. Nyberg

    1996-01-01

    Two-dimensional (2D) hypercycles have been shown to generate spiral patterns, which may protect the hypercycle from parasites that would be fatal to the hypercycle in a homogeneous spatial distribution. We perform numerical experiments on a partial differential equations hypercycle model and show that scroll rings are formed and are not stable: They contract by a power law and disappear within

  1. INCORPORATING CONCENTRATION DEPENDENCE IN STABLE ISOTOPE MIXING MODELS

    EPA Science Inventory

    Stable isotopes are often used as natural labels to quantify the contributions of multiple sources to a mixture. For example, C and N isotopic signatures can be used to determine the fraction of three food sources in a consumer's diet. The standard dual isotope, three source li...

  2. INCORPORATING CONCENTRATION DEPENDENCE IN STABLE ISOTOPE MIXING MODELS

    EPA Science Inventory

    Stable isotopes are frequently used to quantify the contributions of multiple sources to a mixture; e.g., C and N isotopic signatures can be used to determine the fraction of three food sources in a consumer's diet. The standard dual isotope, three source linear mixing model ass...

  3. Investigating surface waterwell interaction using stable isotope ratios of water*

    E-print Network

    wellshaveappreciablesurfacewatercontributionsandarepotentially vulnerable to contaminants in the surface water. When looking at wells with more than 6 sampling underlying the city and the river. Numerical ground- water-flow modeling (Hunt et al., 2003; Chapel et alInvestigating surface water­well interaction using stable isotope ratios of water* Randall J. Hunta

  4. From birds to butterflies: animal movement patterns and stable isotopes

    Microsoft Academic Search

    Dustin R. Rubenstein; Keith A. Hobson

    2004-01-01

    Establishing patterns of movement of wild animals is crucial for our understanding of their ecology, life history and behavior, and is a prerequisite for their effective conservation. Advances in the use of stable isotope markers make it possible to track a diversity of animal species in a variety of habitats. This approach is revolutionizing the way in which we make

  5. Stable isotopes as one of nature's ecological recorders

    Microsoft Academic Search

    Jason B. West; Gabriel J. Bowen; Thure E. Cerling; James R. Ehleringer

    2006-01-01

    Analyses of the natural variation in stable isotopes of components of ecological systems have provided new insights into how these systems function across paleoecological to modern timescales and across a wide range of spatial scales. Isotope abundances of the molecules in biological materials and geochemical profiles are viewed as recorders that can be used to reconstruct ecological processes or to

  6. ORIGINAL PAPER North American transect of stable hydrogen and oxygen

    E-print Network

    Bern, Universität

    ORIGINAL PAPER North American transect of stable hydrogen and oxygen isotopes in water beetles from a dataset of chitin dD and d18 O in two genera of water beetles from a museum collection containing 40 locations for Helophorus (water scavenging beetles) and 48 locations for Hydroporus (predaceous diving

  7. Review: Stable oxygen isotope composition of plant tissue: a review

    Microsoft Academic Search

    Margaret M. Barbour

    2007-01-01

    With the development of rapid measurement techniques, stable oxygen isotope analysis of plant tissue is poised to become an important tool in plant physiological, ecological, paleoclimatic and forensic studies. Recent advances in mechanistic understanding have led to the improvement of process-based models that accurately predict variability in the oxygen isotope composition of plant organic material (?18Op). ?18Op has been shown

  8. Detection of alternative stable states in marine communities

    E-print Network

    Plotkin, Joshua B.

    , rocky intertidal systems, soft-sediment beds, and subtidal systems are briefly reviewed. Suggestions or environmental conditions that initiates the switch from one state to the other. Knowlton (1992) suggested the switch between alternative stable states should occur at a critical environmental threshold. The critical

  9. A stable lotus-leaf-like water-repellent copper

    Microsoft Academic Search

    Zhi-Guang Guo; Wei-Min Liu; Bao-Lian Su

    2008-01-01

    The stable lotus-leaf-like superhydrophobic copper was fabricated by means of a very simple and industrially up scalable method. Under both the growth of CuO microcrystals on the surface and the chemical modification, the wettability of the copper substrate changed from hydrophilic to water-repellent superhydrophobic, with surface hierarchical structures similar to that of lotus leaf.

  10. A stable lotus-leaf-like water-repellent copper

    NASA Astrophysics Data System (ADS)

    Guo, Zhi-Guang; Liu, Wei-Min; Su, Bao-Lian

    2008-02-01

    The stable lotus-leaf-like superhydrophobic copper was fabricated by means of a very simple and industrially up scalable method. Under both the growth of CuO microcrystals on the surface and the chemical modification, the wettability of the copper substrate changed from hydrophilic to water-repellent superhydrophobic, with surface hierarchical structures similar to that of lotus leaf.

  11. Carbon Stable Isotopes as Indicators of Coastal Eutrophication

    EPA Science Inventory

    Coastal ecologists and managers have frequently used nitrogen stable isotopes (d15N) to trace and monitor anthropogenic nitrogen (N) in coastal ecosystems. However, the interpretation of d15N data can often be challenging, if not confounding, as the isotope values fractionate su...

  12. STABLE ISOTOPE TRACER MARKING OF INDIVIDUAL BOLL WEEVILS

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Stable isotope markers have been used to study animal nutrition for several decades and more recently to study the foraging and cultural habits of imported fire ants. In this work, we have extended that effort to evaluate the potential for marking boll weevils with the rare earth element samarium. ...

  13. Resources on Isotopes: Fundamentals of Stable Isotope Geochemistry

    NSDL National Science Digital Library

    This is a brief review of some of the fundamentals of stable isotope geochemistry, including definitions, terminology, basic principles, standards, and guidelines on reporting data. Users can follow the link on the top right for the periodic table and read about the isotopic systems of several dozen elements.

  14. Development of stable isotope mixing models in ecology - Fremantle

    EPA Science Inventory

    More than 40 years ago, stable isotope analysis methods used in geochemistry began to be applied to ecological studies. One common application is using mathematical mixing models to sort out the proportional contributions of various sources to a mixture. Examples include contri...

  15. Development of stable isotope mixing models in ecology - Sydney

    EPA Science Inventory

    More than 40 years ago, stable isotope analysis methods used in geochemistry began to be applied to ecological studies. One common application is using mathematical mixing models to sort out the proportional contributions of various sources to a mixture. Examples include contri...

  16. STABLE ISOTOPE PROBING TO INVESTIGATE MICROBIAL FUNCTION IN SOIL

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Most approaches for in situ phylogenetic characterization of soil microorganisms lack the ability to establish a causal relationship to function within the community. Recently, the use of stable isotopes to label phylogenetically informative biomolecules (phospholipid fatty acids, DNA, or RNA), typ...

  17. Development of stable isotope mixing models in ecology - Dublin

    EPA Science Inventory

    More than 40 years ago, stable isotope analysis methods used in geochemistry began to be applied to ecological studies. One common application is using mathematical mixing models to sort out the proportional contributions of various sources to a mixture. Examples include contri...

  18. Development of stable isotope mixing models in ecology - Perth

    EPA Science Inventory

    More than 40 years ago, stable isotope analysis methods used in geochemistry began to be applied to ecological studies. One common application is using mathematical mixing models to sort out the proportional contributions of various sources to a mixture. Examples include contri...

  19. Effects of particle shape and mobility on stable armor development

    Microsoft Academic Search

    Basil Gomez

    1994-01-01

    The relative size and roughness of a stable armor varies with particle shape. For a given imposed shear stress the order of increasing nominal particle diameter is flat, angular, and rounded gravel. The order of increasing surface roughness is flat, rounded, and angular gravel. The mobility of fine flat gravel particles is enhanced by the lower surface roughness of armors

  20. Unconditionally stable nearly PML algorithm for linear dispersive media

    Microsoft Academic Search

    Omar Ramadan

    2005-01-01

    Unconditional stable alternating direction implicit (ADI) formulations of the nearly perfectly matched layer (NPML) are presented for truncating linear dispersive finite difference time domain (FDTD) grids. The digital signal processing (DSP) algorithms developed for digital filters are used to implement the frequency dependent property of the media into the ADI-FDTD algorithm. The formulations have the advantage of simplicity of ADI-FDTD